diff --git a/core/modules/action/tests/src/Functional/ActionListTest.php b/core/modules/action/tests/src/Functional/ActionListTest.php
index 6bb753e5e7a35849b9fe82dc92fe15430352ce87..10e6637af6a873143cf486477771b1c4cb5d951d 100644
--- a/core/modules/action/tests/src/Functional/ActionListTest.php
+++ b/core/modules/action/tests/src/Functional/ActionListTest.php
@@ -18,6 +18,11 @@ class ActionListTest extends BrowserTestBase {
    */
   public static $modules = ['action'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the behavior when there are no actions to list in the admin page.
    */
diff --git a/core/modules/action/tests/src/Functional/ActionUninstallTest.php b/core/modules/action/tests/src/Functional/ActionUninstallTest.php
index 76170b16699790b738d9e45217e51aeaf8999566..5e3718044e52b1c197f02c062ade8104baaa8cd3 100644
--- a/core/modules/action/tests/src/Functional/ActionUninstallTest.php
+++ b/core/modules/action/tests/src/Functional/ActionUninstallTest.php
@@ -20,6 +20,11 @@ class ActionUninstallTest extends BrowserTestBase {
    */
   public static $modules = ['views', 'action'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests Action uninstall.
    */
diff --git a/core/modules/action/tests/src/Functional/ConfigurationTest.php b/core/modules/action/tests/src/Functional/ConfigurationTest.php
index 9b9dcf62a07f9a4df76cb3826e71df8ebf8ca787..06510ecc80aa3065601afee672f562324e8ed05d 100644
--- a/core/modules/action/tests/src/Functional/ConfigurationTest.php
+++ b/core/modules/action/tests/src/Functional/ConfigurationTest.php
@@ -20,6 +20,12 @@ class ConfigurationTest extends BrowserTestBase {
    */
   public static $modules = ['action'];
 
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests configuration of advanced actions through administration interface.
    */
diff --git a/core/modules/action/tests/src/FunctionalJavascript/ActionFormAjaxTest.php b/core/modules/action/tests/src/FunctionalJavascript/ActionFormAjaxTest.php
index f4c85fc755d7054c1d9706bb9f449bfc6e607d33..e32e87f67114d3661b1e52192475fd192c5224c2 100644
--- a/core/modules/action/tests/src/FunctionalJavascript/ActionFormAjaxTest.php
+++ b/core/modules/action/tests/src/FunctionalJavascript/ActionFormAjaxTest.php
@@ -18,6 +18,11 @@ class ActionFormAjaxTest extends WebDriverTestBase {
    */
   protected static $modules = ['action', 'action_form_ajax_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/AddFeedTest.php b/core/modules/aggregator/tests/src/Functional/AddFeedTest.php
index 88a1547b72281f02bcede253b58cddd8cf18bfbd..8809690b9ef995c86cb6acdf414a90da7acf8bc8 100644
--- a/core/modules/aggregator/tests/src/Functional/AddFeedTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AddFeedTest.php
@@ -11,6 +11,11 @@
  */
 class AddFeedTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/aggregator/tests/src/Functional/AggregatorAdminTest.php b/core/modules/aggregator/tests/src/Functional/AggregatorAdminTest.php
index 53c1745a800f64f3d11d5f317350e4c68abb4e4b..0378cf733cf0b93941247277675f12eb44769719 100644
--- a/core/modules/aggregator/tests/src/Functional/AggregatorAdminTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AggregatorAdminTest.php
@@ -11,6 +11,11 @@
  */
 class AggregatorAdminTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the settings form to ensure the correct default values are used.
    */
diff --git a/core/modules/aggregator/tests/src/Functional/AggregatorCronTest.php b/core/modules/aggregator/tests/src/Functional/AggregatorCronTest.php
index 4a3ca0b07d9016e048a41b7d6de59c3a60bf66e6..acc6b61b5fb27d45b2b9da772e7bdba90f2afbc2 100644
--- a/core/modules/aggregator/tests/src/Functional/AggregatorCronTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AggregatorCronTest.php
@@ -13,6 +13,11 @@ class AggregatorCronTest extends AggregatorTestBase {
 
   use CronRunTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Adds feeds and updates them via cron process.
    */
diff --git a/core/modules/aggregator/tests/src/Functional/AggregatorDisplayConfigurableTest.php b/core/modules/aggregator/tests/src/Functional/AggregatorDisplayConfigurableTest.php
index 0a2dcb652bf2565c5e701400d7541d9d0468d793..e48816c284d999cbf677ca0417ed66ef610b52ef 100644
--- a/core/modules/aggregator/tests/src/Functional/AggregatorDisplayConfigurableTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AggregatorDisplayConfigurableTest.php
@@ -13,6 +13,11 @@
  */
 class AggregatorDisplayConfigurableTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/AggregatorRenderingTest.php b/core/modules/aggregator/tests/src/Functional/AggregatorRenderingTest.php
index 1c58269af567a0383728d9242674d0139946cc22..522ea02f3480a2ad5be761cad2811dbdd7ce9dae 100644
--- a/core/modules/aggregator/tests/src/Functional/AggregatorRenderingTest.php
+++ b/core/modules/aggregator/tests/src/Functional/AggregatorRenderingTest.php
@@ -19,6 +19,11 @@ class AggregatorRenderingTest extends AggregatorTestBase {
    */
   public static $modules = ['block', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/aggregator/tests/src/Functional/DeleteFeedItemTest.php b/core/modules/aggregator/tests/src/Functional/DeleteFeedItemTest.php
index f70711624aceca6c5b84d9b3c599bbf481a399cc..b7cd108edd5f113dd78423ef6a08f4db93b49f32 100644
--- a/core/modules/aggregator/tests/src/Functional/DeleteFeedItemTest.php
+++ b/core/modules/aggregator/tests/src/Functional/DeleteFeedItemTest.php
@@ -11,6 +11,11 @@
  */
 class DeleteFeedItemTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests running "delete items" from 'admin/config/services/aggregator' page.
    */
diff --git a/core/modules/aggregator/tests/src/Functional/DeleteFeedTest.php b/core/modules/aggregator/tests/src/Functional/DeleteFeedTest.php
index 67fe2767f097d59ec2d8d1d23a9f4d64d418b103..9ff7b3435ba1642412f377dedf343f71443c504f 100644
--- a/core/modules/aggregator/tests/src/Functional/DeleteFeedTest.php
+++ b/core/modules/aggregator/tests/src/Functional/DeleteFeedTest.php
@@ -16,6 +16,11 @@ class DeleteFeedTest extends AggregatorTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Deletes a feed and ensures that all of its services are deleted.
    */
diff --git a/core/modules/aggregator/tests/src/Functional/FeedAdminDisplayTest.php b/core/modules/aggregator/tests/src/Functional/FeedAdminDisplayTest.php
index e057be6e613bee28705190ce4be5eae1103b2458..ec327a595e72e870c1adcc89c4fbae67645139c9 100644
--- a/core/modules/aggregator/tests/src/Functional/FeedAdminDisplayTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedAdminDisplayTest.php
@@ -9,6 +9,11 @@
  */
 class FeedAdminDisplayTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the "Next update" and "Last update" fields.
    */
diff --git a/core/modules/aggregator/tests/src/Functional/FeedCacheTagsTest.php b/core/modules/aggregator/tests/src/Functional/FeedCacheTagsTest.php
index 0cf6d1d031214d1ea931cc7db62359934a1c44f0..b1efd4609c51b72b563c5bece5247194cef6f46b 100644
--- a/core/modules/aggregator/tests/src/Functional/FeedCacheTagsTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedCacheTagsTest.php
@@ -19,6 +19,11 @@ class FeedCacheTagsTest extends EntityWithUriCacheTagsTestBase {
    */
   public static $modules = ['aggregator'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/FeedFetcherPluginTest.php b/core/modules/aggregator/tests/src/Functional/FeedFetcherPluginTest.php
index 1a03186c63b1487e591c898f30b5450a4cf81d53..cdc2c337f9a536a6ef39e4301a01c0f3e162353f 100644
--- a/core/modules/aggregator/tests/src/Functional/FeedFetcherPluginTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedFetcherPluginTest.php
@@ -11,6 +11,11 @@
  */
 class FeedFetcherPluginTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/FeedLanguageTest.php b/core/modules/aggregator/tests/src/Functional/FeedLanguageTest.php
index f9fd91f9c904d566af8a09f2c1c75c52d9141dea..aeb7b997953eed0a5ff4eff92b8215458635d03a 100644
--- a/core/modules/aggregator/tests/src/Functional/FeedLanguageTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedLanguageTest.php
@@ -21,6 +21,11 @@ class FeedLanguageTest extends AggregatorTestBase {
    */
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * List of langcodes.
    *
diff --git a/core/modules/aggregator/tests/src/Functional/FeedParserTest.php b/core/modules/aggregator/tests/src/Functional/FeedParserTest.php
index 71e88212cbfd81dd78a84bec8481a8007a91e836..82cea3ff9e238c39c210158e7d2e9b04b002dc07 100644
--- a/core/modules/aggregator/tests/src/Functional/FeedParserTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedParserTest.php
@@ -15,6 +15,11 @@
  */
 class FeedParserTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/FeedProcessorPluginTest.php b/core/modules/aggregator/tests/src/Functional/FeedProcessorPluginTest.php
index 2f95f69db96b75a125eb1460067ad26422bd952e..c21f30573b70e05625ab20d7f01bc308f7470d5d 100644
--- a/core/modules/aggregator/tests/src/Functional/FeedProcessorPluginTest.php
+++ b/core/modules/aggregator/tests/src/Functional/FeedProcessorPluginTest.php
@@ -14,6 +14,11 @@
  */
 class FeedProcessorPluginTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonAnonTest.php b/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonAnonTest.php
index 56f164b44788bae9611a03b220b52c8838777073..834cf5dd1d7ed16a006d1bcdd7747fd58453d6a5 100644
--- a/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonAnonTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonAnonTest.php
@@ -16,4 +16,9 @@ class FeedHalJsonAnonTest extends FeedHalJsonTestBase {
    */
   protected static $mimeType = 'application/hal+json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonBasicAuthTest.php b/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonBasicAuthTest.php
index 58bb47351a9d11a7d9f3a4cccf630c5ffef110c2..a1d36b3240098464e457a001963ec0b58bc67e58 100644
--- a/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonBasicAuthTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FeedHalJsonBasicAuthTest extends FeedHalJsonTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonCookieTest.php b/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonCookieTest.php
index dd574d988d3693681d872a91c3da6f554eab302e..8aa7a07c3e42cf2800edcf153973d69f75be907e 100644
--- a/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonCookieTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Hal/FeedHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class FeedHalJsonCookieTest extends FeedHalJsonTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonAnonTest.php b/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonAnonTest.php
index 20d37fa1ee733b9fdedf9d1d797e422fc90346c6..629e794a9e38afc133cded730f406c95a1a9e35c 100644
--- a/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonAnonTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonAnonTest.php
@@ -16,6 +16,11 @@ class ItemHalJsonAnonTest extends ItemHalJsonTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonBasicAuthTest.php b/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonBasicAuthTest.php
index 767c7025a476638eca9ae37335d23414aba7003d..f8792f5d753c9498b4f34bd23f05db6d22fcf0d6 100644
--- a/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonBasicAuthTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ItemHalJsonBasicAuthTest extends ItemHalJsonTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonCookieTest.php b/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonCookieTest.php
index 161a7357661aaf7db5f224e5ad4a3e15a74a7469..d180934ab989f57a068c50f9f127f038c1eb2f17 100644
--- a/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonCookieTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Hal/ItemHalJsonCookieTest.php
@@ -16,6 +16,11 @@ class ItemHalJsonCookieTest extends ItemHalJsonTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/ImportOpmlTest.php b/core/modules/aggregator/tests/src/Functional/ImportOpmlTest.php
index f9099e0eb8210bf54962ea88cec23f5ecede372d..89cc07eacab3487004076f32f850dcb2dcc5da64 100644
--- a/core/modules/aggregator/tests/src/Functional/ImportOpmlTest.php
+++ b/core/modules/aggregator/tests/src/Functional/ImportOpmlTest.php
@@ -18,6 +18,11 @@ class ImportOpmlTest extends AggregatorTestBase {
    */
   public static $modules = ['block', 'help'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/ItemCacheTagsTest.php b/core/modules/aggregator/tests/src/Functional/ItemCacheTagsTest.php
index edd2ac32a92cb601ef43522334037cd35f5fe85c..b86cd889e2836aea4c1160371c9115b52a0e9e45 100644
--- a/core/modules/aggregator/tests/src/Functional/ItemCacheTagsTest.php
+++ b/core/modules/aggregator/tests/src/Functional/ItemCacheTagsTest.php
@@ -21,6 +21,11 @@ class ItemCacheTagsTest extends EntityCacheTagsTestBase {
    */
   public static $modules = ['aggregator'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonAnonTest.php b/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonAnonTest.php
index 1550d74607f447ef5bf9387a019966107d51aac5..14664c18b12f8c6245931aa195175d05e2dd609f 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonAnonTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonAnonTest.php
@@ -21,4 +21,9 @@ class FeedJsonAnonTest extends FeedResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonBasicAuthTest.php b/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonBasicAuthTest.php
index e918ab9819a86f4b7dcecdacc77993f08fc0d6eb..6018df892144ec124002803635fd1c1d49090c6a 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonBasicAuthTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FeedJsonBasicAuthTest extends FeedResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonCookieTest.php b/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonCookieTest.php
index e5e0c86a4815e5aa5ce566f1ecbd45e1c1637437..ef6de7bc63ac192e860b2ebb29cc96540d1cc88e 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonCookieTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/FeedJsonCookieTest.php
@@ -26,4 +26,9 @@ class FeedJsonCookieTest extends FeedResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlAnonTest.php b/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlAnonTest.php
index 41b03a6a8a98d3fd05c919ef5f90c8bf1d56c201..0e2c1c5e76c6cb7b31a800a1540688f8dd6198a3 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlAnonTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlAnonTest.php
@@ -23,4 +23,9 @@ class FeedXmlAnonTest extends FeedResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlBasicAuthTest.php b/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlBasicAuthTest.php
index 450cc49effdc75f8774c45e7225eb85f81711c58..c4bb7426d1a17f5f38552eab8f08b2a220b7ad8d 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlBasicAuthTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class FeedXmlBasicAuthTest extends FeedResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlCookieTest.php b/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlCookieTest.php
index 3fee585d07e2e9d60e6918961b7f66bae401c69c..727609a5696bc4091c792f1c3a869f0cf2dd3062 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlCookieTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/FeedXmlCookieTest.php
@@ -28,4 +28,9 @@ class FeedXmlCookieTest extends FeedResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonAnonTest.php b/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonAnonTest.php
index 13e24c3a454093821e704a339bce599372ff2efa..130a2af5cd87d871f592162cd312b4e447a15891 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonAnonTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonAnonTest.php
@@ -21,4 +21,9 @@ class ItemJsonAnonTest extends ItemResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonBasicAuthTest.php b/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonBasicAuthTest.php
index 15f800d1384d34976f44dda8129697fe970a83b0..383e8b59b3bcd8eb066da7bc0baac11737bb6bfd 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonBasicAuthTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ItemJsonBasicAuthTest extends ItemResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonCookieTest.php b/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonCookieTest.php
index 1e6567b3e9e5e882a031dfe7dbdc293935331d94..587789949529d01b484c3bc953bcceb9ebf72272 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonCookieTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/ItemJsonCookieTest.php
@@ -26,4 +26,9 @@ class ItemJsonCookieTest extends ItemResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlAnonTest.php b/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlAnonTest.php
index f61a87841370366b654fba9ab1a2fe7b5053c561..e9ce5ddc0abb83013bf489b828a6f3fd19c7377b 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlAnonTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlAnonTest.php
@@ -23,4 +23,9 @@ class ItemXmlAnonTest extends ItemResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlBasicAuthTest.php b/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlBasicAuthTest.php
index 438a4233ca70ccce77f8888df236b284d911c3a2..4de90303d127f57cce3102aa99c0525438440002 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlBasicAuthTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ItemXmlBasicAuthTest extends ItemResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlCookieTest.php b/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlCookieTest.php
index 69144066ad43b9bd4005009e6952a312954d6c71..a541956e9a30b50a8f1a7a83f6d449c82f33aace 100644
--- a/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlCookieTest.php
+++ b/core/modules/aggregator/tests/src/Functional/Rest/ItemXmlCookieTest.php
@@ -28,4 +28,9 @@ class ItemXmlCookieTest extends ItemResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php b/core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php
index 2e4015e8664ce8b440fd9501ae31051afea9acf0..7aef9ac0f9948b5b490db9001921758e5760a653 100644
--- a/core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php
+++ b/core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php
@@ -13,6 +13,11 @@
  */
 class UpdateFeedItemTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests running "update items" from 'admin/config/services/aggregator' page.
    */
diff --git a/core/modules/aggregator/tests/src/Functional/UpdateFeedTest.php b/core/modules/aggregator/tests/src/Functional/UpdateFeedTest.php
index 62e5c4227b4e70f88688987f2d07aa7c243b89b4..a7ee2436cadf590ac6337ebaf760d40823c4feaa 100644
--- a/core/modules/aggregator/tests/src/Functional/UpdateFeedTest.php
+++ b/core/modules/aggregator/tests/src/Functional/UpdateFeedTest.php
@@ -11,6 +11,11 @@
  */
 class UpdateFeedTest extends AggregatorTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Creates a feed and attempts to update it.
    */
diff --git a/core/modules/ban/tests/src/Functional/IpAddressBlockingTest.php b/core/modules/ban/tests/src/Functional/IpAddressBlockingTest.php
index 68451dd0be942c64d10d13645a828495b15063e1..bb77517e40b93443bfb7a1e633a52a84276a14b0 100644
--- a/core/modules/ban/tests/src/Functional/IpAddressBlockingTest.php
+++ b/core/modules/ban/tests/src/Functional/IpAddressBlockingTest.php
@@ -20,6 +20,11 @@ class IpAddressBlockingTest extends BrowserTestBase {
    */
   public static $modules = ['ban'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests various user input to confirm correct validation and saving of data.
    */
diff --git a/core/modules/basic_auth/tests/src/Functional/BasicAuthTest.php b/core/modules/basic_auth/tests/src/Functional/BasicAuthTest.php
index fc69ee591266c41f331c988ad96d054ba3e175d1..55b7fc15ead2d79ba164ee64d1d74339a05b922d 100644
--- a/core/modules/basic_auth/tests/src/Functional/BasicAuthTest.php
+++ b/core/modules/basic_auth/tests/src/Functional/BasicAuthTest.php
@@ -25,6 +25,11 @@ class BasicAuthTest extends BrowserTestBase {
    */
   public static $modules = ['basic_auth', 'router_test', 'locale', 'basic_auth_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test http basic authentication.
    */
diff --git a/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
index 4fa7408ac2b92da28b123808940b918fe07709df..a9b5eb4a441b6b278240f5ca78d0ae5def42dc53 100644
--- a/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
+++ b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
@@ -33,6 +33,11 @@ class BigPipeTest extends BrowserTestBase {
    */
   public static $modules = ['big_pipe', 'big_pipe_test', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/big_pipe/tests/src/FunctionalJavascript/BigPipeRegressionTest.php b/core/modules/big_pipe/tests/src/FunctionalJavascript/BigPipeRegressionTest.php
index 7eccf4be26f57b18d5e1a93043d265ad7bdeebdc..61fa6d950a93c451ee58b76f063f9fbee885191b 100644
--- a/core/modules/big_pipe/tests/src/FunctionalJavascript/BigPipeRegressionTest.php
+++ b/core/modules/big_pipe/tests/src/FunctionalJavascript/BigPipeRegressionTest.php
@@ -34,6 +34,11 @@ class BigPipeRegressionTest extends WebDriverTestBase {
     'big_pipe_regression_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/BlockAdminThemeTest.php b/core/modules/block/tests/src/Functional/BlockAdminThemeTest.php
index 9811b21694973e264fbee830c99977b6f5b3c9f6..52dbc4d4c5bd9441a9117c93dfdb2d596f86a23b 100644
--- a/core/modules/block/tests/src/Functional/BlockAdminThemeTest.php
+++ b/core/modules/block/tests/src/Functional/BlockAdminThemeTest.php
@@ -18,6 +18,11 @@ class BlockAdminThemeTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'contextual'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Check for the accessibility of the admin theme on the block admin page.
    */
diff --git a/core/modules/block/tests/src/Functional/BlockCacheTest.php b/core/modules/block/tests/src/Functional/BlockCacheTest.php
index e5bb360e3e66060f88a7ea2f37d8b33945b74f03..513fcddc0c8cd35ed2724eab740c38003ec6c971 100644
--- a/core/modules/block/tests/src/Functional/BlockCacheTest.php
+++ b/core/modules/block/tests/src/Functional/BlockCacheTest.php
@@ -19,6 +19,11 @@ class BlockCacheTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_test', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with permission to create and edit books and to administer blocks.
    *
diff --git a/core/modules/block/tests/src/Functional/BlockDemoTest.php b/core/modules/block/tests/src/Functional/BlockDemoTest.php
index 0c8b117c61d43566cd3e0c4a842739984db980bb..313fc93c47e162dc7f5d3c9068c19e7e933770a3 100644
--- a/core/modules/block/tests/src/Functional/BlockDemoTest.php
+++ b/core/modules/block/tests/src/Functional/BlockDemoTest.php
@@ -18,6 +18,11 @@ class BlockDemoTest extends BrowserTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Check for the accessibility of the admin block demo page.
    */
diff --git a/core/modules/block/tests/src/Functional/BlockFormInBlockTest.php b/core/modules/block/tests/src/Functional/BlockFormInBlockTest.php
index c0e7f589267ef567b68c8456b0734ad2e48d9041..6da8579ebf133ee28d2f2d8eed66ccd99960398a 100644
--- a/core/modules/block/tests/src/Functional/BlockFormInBlockTest.php
+++ b/core/modules/block/tests/src/Functional/BlockFormInBlockTest.php
@@ -19,6 +19,11 @@ class BlockFormInBlockTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_test', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/BlockHiddenRegionTest.php b/core/modules/block/tests/src/Functional/BlockHiddenRegionTest.php
index fe96520eae757307d88c1349772aa1052069bdfd..a1de4739e663fe2ed79fd5153036719b5bf9f0b4 100644
--- a/core/modules/block/tests/src/Functional/BlockHiddenRegionTest.php
+++ b/core/modules/block/tests/src/Functional/BlockHiddenRegionTest.php
@@ -24,6 +24,11 @@ class BlockHiddenRegionTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_test', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/block/tests/src/Functional/BlockHookOperationTest.php b/core/modules/block/tests/src/Functional/BlockHookOperationTest.php
index 23b1f0ce5fd3e4f845a9aec5a068bd18d64fee47..c8837da6849c913cbbb58e38bb54ecf75f3210cc 100644
--- a/core/modules/block/tests/src/Functional/BlockHookOperationTest.php
+++ b/core/modules/block/tests/src/Functional/BlockHookOperationTest.php
@@ -18,6 +18,11 @@ class BlockHookOperationTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/block/tests/src/Functional/BlockHtmlTest.php b/core/modules/block/tests/src/Functional/BlockHtmlTest.php
index 5f9afe916f7d15bfcc27700f3d041e2f39664205..1d5927de81bb37fdb05657948a9072dbf6dbfa2c 100644
--- a/core/modules/block/tests/src/Functional/BlockHtmlTest.php
+++ b/core/modules/block/tests/src/Functional/BlockHtmlTest.php
@@ -18,6 +18,11 @@ class BlockHtmlTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/block/tests/src/Functional/BlockInstallTest.php b/core/modules/block/tests/src/Functional/BlockInstallTest.php
index eb6c5fcebf6e768d70f03eaa78882c07ef433347..78297f9f7a4cd9be47e56cdfa3f7dc26280c6c06 100644
--- a/core/modules/block/tests/src/Functional/BlockInstallTest.php
+++ b/core/modules/block/tests/src/Functional/BlockInstallTest.php
@@ -11,6 +11,11 @@
  */
 class BlockInstallTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testCacheTagInvalidationUponInstallation() {
     // Warm the page cache.
     $this->drupalGet('');
diff --git a/core/modules/block/tests/src/Functional/BlockInvalidRegionTest.php b/core/modules/block/tests/src/Functional/BlockInvalidRegionTest.php
index fe8cdcb56a7884ab8911a4c7d9dc6f797c7f4db5..98babaf6cc50b785197df04017d9ae258e6949dd 100644
--- a/core/modules/block/tests/src/Functional/BlockInvalidRegionTest.php
+++ b/core/modules/block/tests/src/Functional/BlockInvalidRegionTest.php
@@ -20,6 +20,11 @@ class BlockInvalidRegionTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
     // Create an admin user.
diff --git a/core/modules/block/tests/src/Functional/BlockLanguageCacheTest.php b/core/modules/block/tests/src/Functional/BlockLanguageCacheTest.php
index 9ca2b718636de7c648065caedccb9e3e6c1825eb..68570163ba2df4d03ccb116e30faf5e52c3f0aca 100644
--- a/core/modules/block/tests/src/Functional/BlockLanguageCacheTest.php
+++ b/core/modules/block/tests/src/Functional/BlockLanguageCacheTest.php
@@ -19,6 +19,11 @@ class BlockLanguageCacheTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'language', 'menu_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * List of langcodes.
    *
diff --git a/core/modules/block/tests/src/Functional/BlockLanguageTest.php b/core/modules/block/tests/src/Functional/BlockLanguageTest.php
index 1176b052fa174e6b9fead247f066ea9ab39b18db..74ecba2469c508f755fb65c4a6ba7ec77e79adfd 100644
--- a/core/modules/block/tests/src/Functional/BlockLanguageTest.php
+++ b/core/modules/block/tests/src/Functional/BlockLanguageTest.php
@@ -25,6 +25,11 @@ class BlockLanguageTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'block', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/block/tests/src/Functional/BlockRenderOrderTest.php b/core/modules/block/tests/src/Functional/BlockRenderOrderTest.php
index ca9c2c299d0b54f8c449c17bcf1f73118e851300..989e0bf3b83450a3688d880f0a4292eef79f153a 100644
--- a/core/modules/block/tests/src/Functional/BlockRenderOrderTest.php
+++ b/core/modules/block/tests/src/Functional/BlockRenderOrderTest.php
@@ -19,6 +19,11 @@ class BlockRenderOrderTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     // Create a test user.
diff --git a/core/modules/block/tests/src/Functional/BlockSystemBrandingTest.php b/core/modules/block/tests/src/Functional/BlockSystemBrandingTest.php
index 89ce0c4b45a9c8ccad9567b1af0d58ee890f8e96..1c675cf9c6d6f046979357cd5bd172d95262b3b3 100644
--- a/core/modules/block/tests/src/Functional/BlockSystemBrandingTest.php
+++ b/core/modules/block/tests/src/Functional/BlockSystemBrandingTest.php
@@ -16,6 +16,11 @@ class BlockSystemBrandingTest extends BlockTestBase {
    */
   public static $modules = ['block', 'system'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/BlockTest.php b/core/modules/block/tests/src/Functional/BlockTest.php
index 1d653491b856f79e1012c33d1ed9cf9d64291b17..8494946a2f8fa93a819d2a144de7158d54a2c0bf 100644
--- a/core/modules/block/tests/src/Functional/BlockTest.php
+++ b/core/modules/block/tests/src/Functional/BlockTest.php
@@ -16,6 +16,11 @@
  */
 class BlockTest extends BlockTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests block visibility.
    */
diff --git a/core/modules/block/tests/src/Functional/BlockUiTest.php b/core/modules/block/tests/src/Functional/BlockUiTest.php
index f7fc5d52447c61f05a5e2bbd481eb070f9b4a922..a3fc1bb180b886ba80082bfb84418d7f59ee1dc6 100644
--- a/core/modules/block/tests/src/Functional/BlockUiTest.php
+++ b/core/modules/block/tests/src/Functional/BlockUiTest.php
@@ -21,6 +21,11 @@ class BlockUiTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_test', 'help', 'condition_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected $regions;
 
   /**
diff --git a/core/modules/block/tests/src/Functional/BlockXssTest.php b/core/modules/block/tests/src/Functional/BlockXssTest.php
index 3e661d775d3de201f020d429c73a5b383e6064a1..72d38e1ee3c9512021e2b47e773a24d07d4740cf 100644
--- a/core/modules/block/tests/src/Functional/BlockXssTest.php
+++ b/core/modules/block/tests/src/Functional/BlockXssTest.php
@@ -23,6 +23,11 @@ class BlockXssTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_content', 'menu_ui', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests that nothing is escaped other than the blocks explicitly tested.
    */
diff --git a/core/modules/block/tests/src/Functional/Hal/BlockHalJsonAnonTest.php b/core/modules/block/tests/src/Functional/Hal/BlockHalJsonAnonTest.php
index 3069667c2dc0b5747158fe9c310dc7c79507a5f6..8e43483cd4639200be01d42b212d8674eb9abcad 100644
--- a/core/modules/block/tests/src/Functional/Hal/BlockHalJsonAnonTest.php
+++ b/core/modules/block/tests/src/Functional/Hal/BlockHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class BlockHalJsonAnonTest extends BlockResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/Hal/BlockHalJsonBasicAuthTest.php b/core/modules/block/tests/src/Functional/Hal/BlockHalJsonBasicAuthTest.php
index f95f6d732be03958381cd2315cd56097a4d25119..2fb4416e84320a46d630599dd71130c94580220e 100644
--- a/core/modules/block/tests/src/Functional/Hal/BlockHalJsonBasicAuthTest.php
+++ b/core/modules/block/tests/src/Functional/Hal/BlockHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class BlockHalJsonBasicAuthTest extends BlockResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/Hal/BlockHalJsonCookieTest.php b/core/modules/block/tests/src/Functional/Hal/BlockHalJsonCookieTest.php
index 87df9ff580bc9d0f42a3272097934aa09e9882cf..2b907217cfcb24575dfc4821bf57fd0a44bf2996 100644
--- a/core/modules/block/tests/src/Functional/Hal/BlockHalJsonCookieTest.php
+++ b/core/modules/block/tests/src/Functional/Hal/BlockHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class BlockHalJsonCookieTest extends BlockResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/NonDefaultBlockAdminTest.php b/core/modules/block/tests/src/Functional/NonDefaultBlockAdminTest.php
index 43efccb991ce9e8e5dc2a2d0cc57c4afea41ecf1..5564a502231f11b1db0dba2b517c86cf856a1555 100644
--- a/core/modules/block/tests/src/Functional/NonDefaultBlockAdminTest.php
+++ b/core/modules/block/tests/src/Functional/NonDefaultBlockAdminTest.php
@@ -18,6 +18,11 @@ class NonDefaultBlockAdminTest extends BrowserTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/Rest/BlockJsonAnonTest.php b/core/modules/block/tests/src/Functional/Rest/BlockJsonAnonTest.php
index 1d98bcc88d96033d4f923c998e263b9306e8d933..d9e3bb044d065285f0def012f04f274aecfb7555 100644
--- a/core/modules/block/tests/src/Functional/Rest/BlockJsonAnonTest.php
+++ b/core/modules/block/tests/src/Functional/Rest/BlockJsonAnonTest.php
@@ -21,4 +21,9 @@ class BlockJsonAnonTest extends BlockResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
 }
diff --git a/core/modules/block/tests/src/Functional/Rest/BlockJsonBasicAuthTest.php b/core/modules/block/tests/src/Functional/Rest/BlockJsonBasicAuthTest.php
index 9c2a2728265cf9f8ff96e14458edb7e35059657d..c0deb450a5eaf0bba3f175a2912a8255d8808997 100644
--- a/core/modules/block/tests/src/Functional/Rest/BlockJsonBasicAuthTest.php
+++ b/core/modules/block/tests/src/Functional/Rest/BlockJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class BlockJsonBasicAuthTest extends BlockResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/Rest/BlockJsonCookieTest.php b/core/modules/block/tests/src/Functional/Rest/BlockJsonCookieTest.php
index adef298b8b6d3b8920519c31dc7831ca92ca277a..dc00528514854a18479ba1983121b08040a72181 100644
--- a/core/modules/block/tests/src/Functional/Rest/BlockJsonCookieTest.php
+++ b/core/modules/block/tests/src/Functional/Rest/BlockJsonCookieTest.php
@@ -26,4 +26,9 @@ class BlockJsonCookieTest extends BlockResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
 }
diff --git a/core/modules/block/tests/src/Functional/Rest/BlockXmlAnonTest.php b/core/modules/block/tests/src/Functional/Rest/BlockXmlAnonTest.php
index 923f02d83f25a128f5e5e684190349209680ce5c..e7bd8eb6fe6fcbbf1506ad5e0c22d38abfd32a99 100644
--- a/core/modules/block/tests/src/Functional/Rest/BlockXmlAnonTest.php
+++ b/core/modules/block/tests/src/Functional/Rest/BlockXmlAnonTest.php
@@ -23,4 +23,9 @@ class BlockXmlAnonTest extends BlockResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
 }
diff --git a/core/modules/block/tests/src/Functional/Rest/BlockXmlBasicAuthTest.php b/core/modules/block/tests/src/Functional/Rest/BlockXmlBasicAuthTest.php
index 2b720d1d9fc751539227d1a9fe67d1610b4ee61e..0caf4c8b7544df4a482bb051589db05d572e7e4c 100644
--- a/core/modules/block/tests/src/Functional/Rest/BlockXmlBasicAuthTest.php
+++ b/core/modules/block/tests/src/Functional/Rest/BlockXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class BlockXmlBasicAuthTest extends BlockResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block/tests/src/Functional/Rest/BlockXmlCookieTest.php b/core/modules/block/tests/src/Functional/Rest/BlockXmlCookieTest.php
index 9474dbdf0d453e833c2e3635a3be733b20ea2151..be8dc722975835c478bbe6dfe0e88e98e607fb45 100644
--- a/core/modules/block/tests/src/Functional/Rest/BlockXmlCookieTest.php
+++ b/core/modules/block/tests/src/Functional/Rest/BlockXmlCookieTest.php
@@ -28,4 +28,9 @@ class BlockXmlCookieTest extends BlockResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
 }
diff --git a/core/modules/block/tests/src/Functional/Views/DisplayBlockTest.php b/core/modules/block/tests/src/Functional/Views/DisplayBlockTest.php
index 17658e462f05a8c6148b113b01961415601eace8..77bb711b72a9a1ec018567e04bee0430fe63bef3 100644
--- a/core/modules/block/tests/src/Functional/Views/DisplayBlockTest.php
+++ b/core/modules/block/tests/src/Functional/Views/DisplayBlockTest.php
@@ -33,6 +33,11 @@ class DisplayBlockTest extends ViewTestBase {
    */
   public static $modules = ['node', 'block_test_views', 'test_page_test', 'contextual', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/block/tests/src/FunctionalJavascript/BlockFilterTest.php b/core/modules/block/tests/src/FunctionalJavascript/BlockFilterTest.php
index e9ecc06526062b249a450183ca7bb8c7d3d252bf..ee9ff5fd3133d09b2704abe26ac83d5f07ef503a 100644
--- a/core/modules/block/tests/src/FunctionalJavascript/BlockFilterTest.php
+++ b/core/modules/block/tests/src/FunctionalJavascript/BlockFilterTest.php
@@ -17,6 +17,11 @@ class BlockFilterTest extends WebDriverTestBase {
    */
   public static $modules = ['user', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentCacheTagsTest.php b/core/modules/block_content/tests/src/Functional/BlockContentCacheTagsTest.php
index 03e0ea3daef3f486dbbb3d340806c1ce882c11bb..c6778cab987b7dd5b44a7b28301ab69d10c64885 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentCacheTagsTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentCacheTagsTest.php
@@ -22,6 +22,11 @@ class BlockContentCacheTagsTest extends EntityCacheTagsTestBase {
    */
   public static $modules = ['block_content'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentContextualLinksTest.php b/core/modules/block_content/tests/src/Functional/BlockContentContextualLinksTest.php
index e4e1a48ac8fdfda1cb1e226ea8214e6f12ae6b01..e81078e9ccfbf4cb195b534f77aba47455639389 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentContextualLinksTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentContextualLinksTest.php
@@ -16,6 +16,11 @@ class BlockContentContextualLinksTest extends BlockContentTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests contextual links.
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentCreationTest.php b/core/modules/block_content/tests/src/Functional/BlockContentCreationTest.php
index a1b5f97a77b3ab006f1192b490723834864da62f..5bfd624e5ca775d113a5e3765ebd86076b4083de 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentCreationTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentCreationTest.php
@@ -23,6 +23,11 @@ class BlockContentCreationTest extends BlockContentTestBase {
    */
   public static $modules = ['block_content_test', 'dblog', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Permissions to grant admin user.
    *
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentListTest.php b/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
index 556dda69c884dc789fda0b0e08d3b5f857ee61d0..ae56cda1fc13790a267db3599ff5ced3e2cb87cc 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentListTest.php
@@ -22,6 +22,11 @@ class BlockContentListTest extends BlockContentTestBase {
    */
   public static $modules = ['block', 'block_content', 'config_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests the custom block listing page.
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentListViewsTest.php b/core/modules/block_content/tests/src/Functional/BlockContentListViewsTest.php
index 186b32d40881101b544b782e5798df2bd2b38e62..ca896c613f96ab35c94c631266a1aa2a825f706f 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentListViewsTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentListViewsTest.php
@@ -20,6 +20,11 @@ class BlockContentListViewsTest extends BlockContentTestBase {
    */
   public static $modules = ['block', 'block_content', 'config_translation', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the custom block listing page.
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentPageViewTest.php b/core/modules/block_content/tests/src/Functional/BlockContentPageViewTest.php
index 355faf1f0f4a3c87faee0e2ac9117e2baade6c06..c9bc68b0f3c18abd5f0da9ed39f21ebc8449ef3a 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentPageViewTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentPageViewTest.php
@@ -16,6 +16,11 @@ class BlockContentPageViewTest extends BlockContentTestBase {
    */
   public static $modules = ['block_content_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Checks block edit and fallback functionality.
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentRevisionsTest.php b/core/modules/block_content/tests/src/Functional/BlockContentRevisionsTest.php
index 89708bb73aa1abc9a7b95c5750aa0a9b634d2e46..743f85a38148d14514775ff01375a3ac475f96ca 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentRevisionsTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentRevisionsTest.php
@@ -14,6 +14,11 @@
  */
 class BlockContentRevisionsTest extends BlockContentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Stores blocks created during the test.
    * @var array
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentSaveTest.php b/core/modules/block_content/tests/src/Functional/BlockContentSaveTest.php
index ce1fe96597fa22985ef56bb6b8aa9e4d75c6321d..5b89d4d1b94ddd30aa824e8b26239299a98f5c8b 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentSaveTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentSaveTest.php
@@ -19,6 +19,11 @@ class BlockContentSaveTest extends BlockContentTestBase {
    */
   public static $modules = ['block_content_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Sets the test up.
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentTranslationUITest.php b/core/modules/block_content/tests/src/Functional/BlockContentTranslationUITest.php
index fc11d782c9912d495ce9114a96f06d14cba26387..09d0fd95acb6a67b5874cfecd8f8b439071e070d 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentTranslationUITest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentTranslationUITest.php
@@ -27,6 +27,11 @@ class BlockContentTranslationUITest extends ContentTranslationUITestBase {
     'block_content',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentTypeTest.php b/core/modules/block_content/tests/src/Functional/BlockContentTypeTest.php
index 452bea07863eaf6c4394ef4824b9d921e94c63eb..2e172551318e89a56c82ba96c171a3db0d1c1d6b 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentTypeTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentTypeTest.php
@@ -23,6 +23,11 @@ class BlockContentTypeTest extends BlockContentTestBase {
    */
   public static $modules = ['field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Permissions to grant admin user.
    *
diff --git a/core/modules/block_content/tests/src/Functional/BlockContentValidationTest.php b/core/modules/block_content/tests/src/Functional/BlockContentValidationTest.php
index 7baaffd4074fc9615fae5371b8351f6dafd7bbe9..293234ba523576d6bf87e94d684a726553ca1e8a 100644
--- a/core/modules/block_content/tests/src/Functional/BlockContentValidationTest.php
+++ b/core/modules/block_content/tests/src/Functional/BlockContentValidationTest.php
@@ -11,6 +11,11 @@
  */
 class BlockContentValidationTest extends BlockContentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the block content validation constraints.
    */
diff --git a/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonAnonTest.php b/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonAnonTest.php
index 33c1108d24864334da0ad7ca1fcbafaeb6600275..6f7a1b6147c9f81d078f92bfaea879a42f392b11 100644
--- a/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonAnonTest.php
+++ b/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class BlockContentHalJsonAnonTest extends BlockContentResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonBasicAuthTest.php b/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonBasicAuthTest.php
index b9b262e9bedc4fdb931757fe3b4a982303ec0d5a..074eadd81fc9074906a994c744345cffb75d905a 100644
--- a/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonBasicAuthTest.php
+++ b/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class BlockContentHalJsonBasicAuthTest extends BlockContentHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonCookieTest.php b/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonCookieTest.php
index 2446dfb657bc17421f9cc6a4dc416393b58954c9..a751dae70c2b5f089a62ef0c81b69bef994a1c7d 100644
--- a/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonCookieTest.php
+++ b/core/modules/block_content/tests/src/Functional/Hal/BlockContentHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class BlockContentHalJsonCookieTest extends BlockContentHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonAnonTest.php b/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonAnonTest.php
index 3bfff1068a81007301297586638945e12affd344..1a7d4e7056d60d85665dfdcb0dd0377e68cf2f8a 100644
--- a/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonAnonTest.php
+++ b/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class BlockContentTypeHalJsonAnonTest extends BlockContentTypeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonBasicAuthTest.php b/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonBasicAuthTest.php
index 6112c2b60a716528e15ea896da9571ff512da431..41eeb87328ed19d4405940ebca411d6bc1af4056 100644
--- a/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonBasicAuthTest.php
+++ b/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class BlockContentTypeHalJsonBasicAuthTest extends BlockContentTypeResourceTestB
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonCookieTest.php b/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonCookieTest.php
index 889d775cde401983942ad421481fbb7141eaf01f..006d08bfbae9a2b6274ea99bfcfbba5c0f09f90d 100644
--- a/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonCookieTest.php
+++ b/core/modules/block_content/tests/src/Functional/Hal/BlockContentTypeHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class BlockContentTypeHalJsonCookieTest extends BlockContentTypeResourceTestBase
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/PageEditTest.php b/core/modules/block_content/tests/src/Functional/PageEditTest.php
index 3edd7108e914ca139b245c9f8f003112165cd110..1cc8c1946caeebeb62b2202a1bcd14cd05643559 100644
--- a/core/modules/block_content/tests/src/Functional/PageEditTest.php
+++ b/core/modules/block_content/tests/src/Functional/PageEditTest.php
@@ -12,6 +12,11 @@
  */
 class PageEditTest extends BlockContentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonAnonTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonAnonTest.php
index 844f9278b5896a4aa54e5f3084ca0e165da30fe6..31a60f1f591dc7dba3ab14da61ec74c38f100c6e 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonAnonTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonAnonTest.php
@@ -21,4 +21,9 @@ class BlockContentJsonAnonTest extends BlockContentResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonBasicAuthTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonBasicAuthTest.php
index 63bf314eb511017e5fce4d3492950320d8e402f9..f87ce906d76da62af8544f1b6e6d3648d30dd730 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonBasicAuthTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class BlockContentJsonBasicAuthTest extends BlockContentResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonCookieTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonCookieTest.php
index 4c277340723379e14c74925fe23b5ccf69d0faf0..c4eaf0742f781722a1bd11c8461e7a3696bc2360 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonCookieTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentJsonCookieTest.php
@@ -26,4 +26,9 @@ class BlockContentJsonCookieTest extends BlockContentResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonAnonTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonAnonTest.php
index 3fcbd43f53e177d9e8aafbd7c12b40e53782af18..244e43889acdab5abc168251fdf39501145f3f37 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonAnonTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonAnonTest.php
@@ -21,4 +21,9 @@ class BlockContentTypeJsonAnonTest extends BlockContentTypeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonBasicAuthTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonBasicAuthTest.php
index a993d1f1bd5a5480abd176177796096982839b15..709dcfd5d47bcaf2d99ade6b1beca775ac0bc2c3 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonBasicAuthTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class BlockContentTypeJsonBasicAuthTest extends BlockContentTypeResourceTestBase
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonCookieTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonCookieTest.php
index c938f1393d717ec2470c8de1f2989d2a564b65e9..7746171cd44e3905a2bb78297ca2cb9b736ee527 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonCookieTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeJsonCookieTest.php
@@ -26,4 +26,9 @@ class BlockContentTypeJsonCookieTest extends BlockContentTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlAnonTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlAnonTest.php
index 2277d6b9788fa6d8986397e9358d10fd98639d68..cade87714a0177e53d2a4e8abe3095233b8efc05 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlAnonTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlAnonTest.php
@@ -23,4 +23,9 @@ class BlockContentTypeXmlAnonTest extends BlockContentTypeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlBasicAuthTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlBasicAuthTest.php
index a878c7d5b3cd9d926f20a4992413c43695587f59..17b834700d6eeb919d2c5b9dfb721fe106e38456 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlBasicAuthTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class BlockContentTypeXmlBasicAuthTest extends BlockContentTypeResourceTestBase
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlCookieTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlCookieTest.php
index 836c330dcea32ecc5f3a9323a8dbdf612bea428b..bee3ed83d4d5c9922e3e8fd61c36770972e263f3 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlCookieTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentTypeXmlCookieTest.php
@@ -28,4 +28,9 @@ class BlockContentTypeXmlCookieTest extends BlockContentTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlAnonTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlAnonTest.php
index fba08ed473fcf8718b28f503f2e0e6abdb7a2ba1..d32cb121786bc17aa6f4a10e9a91f20e630079fb 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlAnonTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlAnonTest.php
@@ -23,4 +23,9 @@ class BlockContentXmlAnonTest extends BlockContentResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlBasicAuthTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlBasicAuthTest.php
index 199abea08dceb83887b6ae0837c37609540deddc..9b593c9049fdeff3f6c6f89edc80a52fe4dece46 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlBasicAuthTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class BlockContentXmlBasicAuthTest extends BlockContentResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlCookieTest.php b/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlCookieTest.php
index 62514559528fcc61e44d77bec1f6f1df85975d01..ff39556b1163b769acf0f5aadf2b3639c2dddd63 100644
--- a/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlCookieTest.php
+++ b/core/modules/block_content/tests/src/Functional/Rest/BlockContentXmlCookieTest.php
@@ -28,4 +28,9 @@ class BlockContentXmlCookieTest extends BlockContentResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/block_content/tests/src/Functional/UnpublishedBlockTest.php b/core/modules/block_content/tests/src/Functional/UnpublishedBlockTest.php
index 8dbecedf14b78b6214440a2fe3d36856567a34f0..62e41dd327315db0e148e0c66a03334116a202a0 100644
--- a/core/modules/block_content/tests/src/Functional/UnpublishedBlockTest.php
+++ b/core/modules/block_content/tests/src/Functional/UnpublishedBlockTest.php
@@ -20,6 +20,11 @@ class UnpublishedBlockTest extends BrowserTestBase {
    */
   public static $modules = ['block_content'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests unpublishing of block_content entities.
    */
diff --git a/core/modules/block_content/tests/src/Functional/Views/BlockContentFieldFilterTest.php b/core/modules/block_content/tests/src/Functional/Views/BlockContentFieldFilterTest.php
index a77c2e1b297c263da760aa4e5a6815607ebdc407..2a612839af6a2fbabf9b1e8d420d0f5105a6b370 100644
--- a/core/modules/block_content/tests/src/Functional/Views/BlockContentFieldFilterTest.php
+++ b/core/modules/block_content/tests/src/Functional/Views/BlockContentFieldFilterTest.php
@@ -17,6 +17,11 @@ class BlockContentFieldFilterTest extends BlockContentTestBase {
    */
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/block_content/tests/src/Functional/Views/BlockContentIntegrationTest.php b/core/modules/block_content/tests/src/Functional/Views/BlockContentIntegrationTest.php
index 93661578bd9df34229d0a1880bfee8c1f91f3603..8f9e03d25713f8d733f706e51140446b1708c982 100644
--- a/core/modules/block_content/tests/src/Functional/Views/BlockContentIntegrationTest.php
+++ b/core/modules/block_content/tests/src/Functional/Views/BlockContentIntegrationTest.php
@@ -9,6 +9,11 @@
  */
 class BlockContentIntegrationTest extends BlockContentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/block_content/tests/src/Functional/Views/BlockContentRedirectTest.php b/core/modules/block_content/tests/src/Functional/Views/BlockContentRedirectTest.php
index 10ce140e967edd2b39054a1d41a294f23c68f04f..81b206cccf317158a027eca5e33a17b704afb56f 100644
--- a/core/modules/block_content/tests/src/Functional/Views/BlockContentRedirectTest.php
+++ b/core/modules/block_content/tests/src/Functional/Views/BlockContentRedirectTest.php
@@ -23,6 +23,11 @@ class BlockContentRedirectTest extends BlockContentTestBase {
    */
   public static $modules = ['block', 'block_content', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the redirect destination when editing block content.
    */
diff --git a/core/modules/block_content/tests/src/Functional/Views/BlockContentWizardTest.php b/core/modules/block_content/tests/src/Functional/Views/BlockContentWizardTest.php
index 2c59e5c50fe84ec0c7888e02f0d84e0a7d273821..d0c997e216c11cc3cb7b2330371f8390f23df69b 100644
--- a/core/modules/block_content/tests/src/Functional/Views/BlockContentWizardTest.php
+++ b/core/modules/block_content/tests/src/Functional/Views/BlockContentWizardTest.php
@@ -16,6 +16,11 @@ class BlockContentWizardTest extends BlockContentTestBase {
    */
   public static $modules = ['block_content', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/block_content/tests/src/Functional/Views/FieldTypeTest.php b/core/modules/block_content/tests/src/Functional/Views/FieldTypeTest.php
index 8ff2fc05ca0ed94df869e0a61ec599e0842c239c..87a595c5831d5783a4f97b5adaef7d3726d1550f 100644
--- a/core/modules/block_content/tests/src/Functional/Views/FieldTypeTest.php
+++ b/core/modules/block_content/tests/src/Functional/Views/FieldTypeTest.php
@@ -11,6 +11,11 @@
  */
 class FieldTypeTest extends BlockContentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/block_place/tests/src/Functional/BlockPlaceTest.php b/core/modules/block_place/tests/src/Functional/BlockPlaceTest.php
index 9666ec1d15d033acddc35d5d6cdea2efc488336f..8eb78254c846e914878537d5333eb1c343858671 100644
--- a/core/modules/block_place/tests/src/Functional/BlockPlaceTest.php
+++ b/core/modules/block_place/tests/src/Functional/BlockPlaceTest.php
@@ -20,6 +20,11 @@ class BlockPlaceTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'block_place', 'toolbar'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests placing blocks as an admin.
    */
diff --git a/core/modules/book/tests/src/Functional/BookBreadcrumbTest.php b/core/modules/book/tests/src/Functional/BookBreadcrumbTest.php
index 5271c8e7b87d492b959b1dad887359eae04a8b77..e539867a233bcdeb2bf49b88e6aa58c51a13a0ac 100644
--- a/core/modules/book/tests/src/Functional/BookBreadcrumbTest.php
+++ b/core/modules/book/tests/src/Functional/BookBreadcrumbTest.php
@@ -18,6 +18,11 @@ class BookBreadcrumbTest extends BrowserTestBase {
    */
   public static $modules = ['book', 'block', 'book_breadcrumb_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A book node.
    *
diff --git a/core/modules/book/tests/src/Functional/BookContentModerationTest.php b/core/modules/book/tests/src/Functional/BookContentModerationTest.php
index b9c7cd28418467ced0d18b6215e67bec883346f8..00c234dafa102fa6116c10a837f11abe7d7bfc0d 100644
--- a/core/modules/book/tests/src/Functional/BookContentModerationTest.php
+++ b/core/modules/book/tests/src/Functional/BookContentModerationTest.php
@@ -22,6 +22,11 @@ class BookContentModerationTest extends BrowserTestBase {
    */
   public static $modules = ['book', 'block', 'book_test', 'content_moderation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/book/tests/src/Functional/BookTest.php b/core/modules/book/tests/src/Functional/BookTest.php
index 0361d49a61e929872ad2a617de6cfb7f977a4ad4..e1e81955d23fda2c1a31581df97ff2c7da359f3d 100644
--- a/core/modules/book/tests/src/Functional/BookTest.php
+++ b/core/modules/book/tests/src/Functional/BookTest.php
@@ -23,6 +23,11 @@ class BookTest extends BrowserTestBase {
    */
   public static $modules = ['book', 'block', 'node_access_test', 'book_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with permission to view a book and access printer-friendly version.
    *
diff --git a/core/modules/book/tests/src/Functional/Views/BookRelationshipTest.php b/core/modules/book/tests/src/Functional/Views/BookRelationshipTest.php
index 30b8a8445a12b011f88c73cc8b0ee21fa289b861..b8e7fa04fee247e0acaef2d7fb20520f2951d971 100644
--- a/core/modules/book/tests/src/Functional/Views/BookRelationshipTest.php
+++ b/core/modules/book/tests/src/Functional/Views/BookRelationshipTest.php
@@ -28,6 +28,11 @@ class BookRelationshipTest extends ViewTestBase {
    */
   public static $modules = ['book_test_views', 'book', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A book node.
    *
diff --git a/core/modules/book/tests/src/FunctionalJavascript/BookJavascriptTest.php b/core/modules/book/tests/src/FunctionalJavascript/BookJavascriptTest.php
index dc9b8125ccccda21dc2cf8eaed836a08081e29cb..7f42954a4e4bfc293e12af0a14eaa526c9beede1 100644
--- a/core/modules/book/tests/src/FunctionalJavascript/BookJavascriptTest.php
+++ b/core/modules/book/tests/src/FunctionalJavascript/BookJavascriptTest.php
@@ -19,6 +19,11 @@ class BookJavascriptTest extends WebDriverTestBase {
    */
   public static $modules = ['book'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests re-ordering of books.
    */
diff --git a/core/modules/ckeditor/tests/src/Functional/CKEditorAdminTest.php b/core/modules/ckeditor/tests/src/Functional/CKEditorAdminTest.php
index aeba60fd7545bc0cd125153ebedca0060c5e6ef9..87c358cd684faec2a7b9881695ec2fc2fa556799 100644
--- a/core/modules/ckeditor/tests/src/Functional/CKEditorAdminTest.php
+++ b/core/modules/ckeditor/tests/src/Functional/CKEditorAdminTest.php
@@ -22,6 +22,11 @@ class CKEditorAdminTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'editor', 'ckeditor'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with the 'administer filters' permission.
    *
diff --git a/core/modules/ckeditor/tests/src/Functional/CKEditorLoadingTest.php b/core/modules/ckeditor/tests/src/Functional/CKEditorLoadingTest.php
index d56919636c6df7cb2873e58324778b5a84266b29..71908383480d848db77df088aeace94f95ccbbcf 100644
--- a/core/modules/ckeditor/tests/src/Functional/CKEditorLoadingTest.php
+++ b/core/modules/ckeditor/tests/src/Functional/CKEditorLoadingTest.php
@@ -20,6 +20,11 @@ class CKEditorLoadingTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'editor', 'ckeditor', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An untrusted user with access to only the 'plain_text' format.
    *
diff --git a/core/modules/ckeditor/tests/src/Functional/CKEditorStylesComboAdminTest.php b/core/modules/ckeditor/tests/src/Functional/CKEditorStylesComboAdminTest.php
index 9f41834de5ba0f1b221f2c267099f4f5ef7be61c..d3ec916ce66c41b1a94f65bf9546d1b4f7399175 100644
--- a/core/modules/ckeditor/tests/src/Functional/CKEditorStylesComboAdminTest.php
+++ b/core/modules/ckeditor/tests/src/Functional/CKEditorStylesComboAdminTest.php
@@ -20,6 +20,11 @@ class CKEditorStylesComboAdminTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'editor', 'ckeditor'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with the 'administer filters' permission.
    *
diff --git a/core/modules/ckeditor/tests/src/Functional/CKEditorToolbarButtonTest.php b/core/modules/ckeditor/tests/src/Functional/CKEditorToolbarButtonTest.php
index c47b67b0b496f170a9e645cb401b9f4730f100ac..821beee47da86c3797e38c8931a9e4d13253fe4c 100644
--- a/core/modules/ckeditor/tests/src/Functional/CKEditorToolbarButtonTest.php
+++ b/core/modules/ckeditor/tests/src/Functional/CKEditorToolbarButtonTest.php
@@ -21,6 +21,11 @@ class CKEditorToolbarButtonTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'editor', 'ckeditor', 'locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/ckeditor/tests/src/FunctionalJavascript/AjaxCssTest.php b/core/modules/ckeditor/tests/src/FunctionalJavascript/AjaxCssTest.php
index ddb53d8303e888b58ab13703e19f74051cab70e4..5dfa7ea45761d37238963b56367e05908c3b9694 100644
--- a/core/modules/ckeditor/tests/src/FunctionalJavascript/AjaxCssTest.php
+++ b/core/modules/ckeditor/tests/src/FunctionalJavascript/AjaxCssTest.php
@@ -18,6 +18,11 @@ class AjaxCssTest extends WebDriverTestBase {
    */
   public static $modules = ['ckeditor', 'ckeditor_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/ckeditor/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php b/core/modules/ckeditor/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
index 82da82519a4e80726388a73bad140954d7f648da..2a66b65ca27c01e9fe8debdb12d67e80f44ff106 100644
--- a/core/modules/ckeditor/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
+++ b/core/modules/ckeditor/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
@@ -20,6 +20,11 @@ class CKEditorIntegrationTest extends WebDriverTestBase {
 
   use CKEditorTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The account.
    *
diff --git a/core/modules/color/tests/src/Functional/ColorConfigSchemaTest.php b/core/modules/color/tests/src/Functional/ColorConfigSchemaTest.php
index 2fa95d1478d2cd0342942940eb16cae9191f612c..001c98c8fa17a25f18b4881d824d8f7afea5abe9 100644
--- a/core/modules/color/tests/src/Functional/ColorConfigSchemaTest.php
+++ b/core/modules/color/tests/src/Functional/ColorConfigSchemaTest.php
@@ -18,6 +18,11 @@ class ColorConfigSchemaTest extends BrowserTestBase {
    */
   public static $modules = ['color'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administrative permissions.
    *
diff --git a/core/modules/color/tests/src/Functional/ColorSafePreviewTest.php b/core/modules/color/tests/src/Functional/ColorSafePreviewTest.php
index fa4e81ecf2df7b4e2d9ce9924c94383f7a6ccb33..34d0d70d159686821dff9a0e903e4d74b251f943 100644
--- a/core/modules/color/tests/src/Functional/ColorSafePreviewTest.php
+++ b/core/modules/color/tests/src/Functional/ColorSafePreviewTest.php
@@ -19,6 +19,11 @@ class ColorSafePreviewTest extends BrowserTestBase {
    */
   public static $modules = ['color', 'color_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administrative permissions.
    *
diff --git a/core/modules/color/tests/src/Functional/ColorTest.php b/core/modules/color/tests/src/Functional/ColorTest.php
index 5e1bf96eccc5225edb64a21ee7bb61ace08f694a..caaa2c9fee9b2444c3f8ed3ce5c4ecff05b79191 100644
--- a/core/modules/color/tests/src/Functional/ColorTest.php
+++ b/core/modules/color/tests/src/Functional/ColorTest.php
@@ -19,6 +19,11 @@ class ColorTest extends BrowserTestBase {
    */
   public static $modules = ['color', 'color_test', 'block', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administrative permissions.
    *
diff --git a/core/modules/comment/tests/src/Functional/CommentAccessTest.php b/core/modules/comment/tests/src/Functional/CommentAccessTest.php
index b2e4725785ae470f3ad9769bb3a36e54d08b2e54..a92fd5e7924d7bd62c6acdfe52b9b714eefc13c5 100644
--- a/core/modules/comment/tests/src/Functional/CommentAccessTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentAccessTest.php
@@ -24,6 +24,11 @@ class CommentAccessTest extends BrowserTestBase {
     'comment',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Node for commenting.
    *
diff --git a/core/modules/comment/tests/src/Functional/CommentActionsTest.php b/core/modules/comment/tests/src/Functional/CommentActionsTest.php
index 326749b7c03c956aa2ed90a3f33a1983b30bc38d..21e1e2dfa6562ca4fe94d928d8a511d758aab727 100644
--- a/core/modules/comment/tests/src/Functional/CommentActionsTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentActionsTest.php
@@ -19,6 +19,11 @@ class CommentActionsTest extends CommentTestBase {
    */
   public static $modules = ['dblog', 'action'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests comment publish and unpublish actions.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentAdminTest.php b/core/modules/comment/tests/src/Functional/CommentAdminTest.php
index 2c8cb172e37ddd8aadb691614c7cc1487adc2782..47a3c6494a58300d73f49f11db7195ac8748ede3 100644
--- a/core/modules/comment/tests/src/Functional/CommentAdminTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentAdminTest.php
@@ -15,6 +15,11 @@
  */
 class CommentAdminTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentAnonymousTest.php b/core/modules/comment/tests/src/Functional/CommentAnonymousTest.php
index 82108496ce9c7d22e8af07f620972963d59d4980..c180531834307a2b7b3a0f3f0bdb3aa61a1ce4e3 100644
--- a/core/modules/comment/tests/src/Functional/CommentAnonymousTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentAnonymousTest.php
@@ -12,6 +12,11 @@
  */
 class CommentAnonymousTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentBlockTest.php b/core/modules/comment/tests/src/Functional/CommentBlockTest.php
index b3ee6b8cfb584df88efcf5aec866c1160686f159..954728bf712e34ed1a09fefb387c8e78c329950b 100644
--- a/core/modules/comment/tests/src/Functional/CommentBlockTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentBlockTest.php
@@ -19,6 +19,11 @@ class CommentBlockTest extends CommentTestBase {
    */
   public static $modules = ['block', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     // Update admin user to have the 'administer blocks' permission.
diff --git a/core/modules/comment/tests/src/Functional/CommentBookTest.php b/core/modules/comment/tests/src/Functional/CommentBookTest.php
index 45693b57fbd0ff586aad446346a97c2bad36c0df..b461f7098abe34dcb941247c3a7205448e837a17 100644
--- a/core/modules/comment/tests/src/Functional/CommentBookTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentBookTest.php
@@ -24,6 +24,11 @@ class CommentBookTest extends BrowserTestBase {
    */
   public static $modules = ['book', 'comment'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentCSSTest.php b/core/modules/comment/tests/src/Functional/CommentCSSTest.php
index c281f63ce38c9422749a3bdbdcccf725319b62e0..54db7a1636d7d92789b95a8a5ac86208d694f4d3 100644
--- a/core/modules/comment/tests/src/Functional/CommentCSSTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentCSSTest.php
@@ -17,6 +17,11 @@ class CommentCSSTest extends CommentTestBase {
 
   use GeneratePermutationsTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentCacheTagsTest.php b/core/modules/comment/tests/src/Functional/CommentCacheTagsTest.php
index 9db678f31a35274cbe350b9c41bde41d51be7b99..43b698689ea94a57555462e9771eaf6febc82ddc 100644
--- a/core/modules/comment/tests/src/Functional/CommentCacheTagsTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentCacheTagsTest.php
@@ -27,6 +27,11 @@ class CommentCacheTagsTest extends EntityWithUriCacheTagsTestBase {
    */
   public static $modules = ['comment'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @var \Drupal\entity_test\Entity\EntityTest
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentEntityTest.php b/core/modules/comment/tests/src/Functional/CommentEntityTest.php
index 9f8eb8c1e2250424c4ed2144ef9d1b83408120dc..79ab591a4a715d692bf293eb9204af5bfa8dffed 100644
--- a/core/modules/comment/tests/src/Functional/CommentEntityTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentEntityTest.php
@@ -25,6 +25,11 @@ class CommentEntityTest extends CommentTestBase {
    */
   public static $modules = ['block', 'comment', 'node', 'history', 'field_ui', 'datetime', 'taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $vocab;
   protected $commentType;
 
diff --git a/core/modules/comment/tests/src/Functional/CommentFieldsTest.php b/core/modules/comment/tests/src/Functional/CommentFieldsTest.php
index 23ec524f3303457b8d82599f41a13a08b88117e2..5223039167955fbca23edd18cc79416a1c39d515 100644
--- a/core/modules/comment/tests/src/Functional/CommentFieldsTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentFieldsTest.php
@@ -22,6 +22,11 @@ class CommentFieldsTest extends CommentTestBase {
    */
   public static $modules = ['field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests that the default 'comment_body' field is correctly added.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentInterfaceTest.php b/core/modules/comment/tests/src/Functional/CommentInterfaceTest.php
index b84ff3dbdbc9892f861256f9e658e3bf493d53f6..9514664b66904e49469d48b11b329f96da9d5ca9 100644
--- a/core/modules/comment/tests/src/Functional/CommentInterfaceTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentInterfaceTest.php
@@ -18,6 +18,11 @@
  */
 class CommentInterfaceTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Set up comments to have subject and preview disabled.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentLanguageTest.php b/core/modules/comment/tests/src/Functional/CommentLanguageTest.php
index f8c21fc843e4033f232634b15d088874c8a8dab2..000ecd28c8c876d08d1923de78c2e227ce43c8f1 100644
--- a/core/modules/comment/tests/src/Functional/CommentLanguageTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentLanguageTest.php
@@ -29,6 +29,11 @@ class CommentLanguageTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'language', 'language_test', 'comment_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentLinksAlterTest.php b/core/modules/comment/tests/src/Functional/CommentLinksAlterTest.php
index e49361b651b81261507af9c7b07b463e43e6102e..7c4349b1bdc5b763e5bb48c676c96788b237b1dc 100644
--- a/core/modules/comment/tests/src/Functional/CommentLinksAlterTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentLinksAlterTest.php
@@ -11,6 +11,11 @@ class CommentLinksAlterTest extends CommentTestBase {
 
   public static $modules = ['comment_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentLinksTest.php b/core/modules/comment/tests/src/Functional/CommentLinksTest.php
index 0b9c4181a19b21175d84c9c794793be1136e0806..34a815c0287bbbee3414f0e98856f9c045dbe2f5 100644
--- a/core/modules/comment/tests/src/Functional/CommentLinksTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentLinksTest.php
@@ -38,6 +38,11 @@ class CommentLinksTest extends CommentTestBase {
    */
   public static $modules = ['views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that comment links are output and can be hidden.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentNewIndicatorTest.php b/core/modules/comment/tests/src/Functional/CommentNewIndicatorTest.php
index b7426ecdad4c37e3099a82f3462b599343671974..99219f1fccaf5df89f9e64b5bd3d1ce849d62334 100644
--- a/core/modules/comment/tests/src/Functional/CommentNewIndicatorTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentNewIndicatorTest.php
@@ -24,6 +24,11 @@ class CommentNewIndicatorTest extends CommentTestBase {
    */
   public static $modules = ['views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Get node "x new comments" metadata from the server for the current user.
    *
diff --git a/core/modules/comment/tests/src/Functional/CommentNodeAccessTest.php b/core/modules/comment/tests/src/Functional/CommentNodeAccessTest.php
index 6842dc137fe64064811976638941a5dd5fcda70a..4b21c492cd29cc1bacd05b7ac01e386f0e9fae50 100644
--- a/core/modules/comment/tests/src/Functional/CommentNodeAccessTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentNodeAccessTest.php
@@ -21,6 +21,11 @@ class CommentNodeAccessTest extends CommentTestBase {
    */
   public static $modules = ['node_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentNodeChangesTest.php b/core/modules/comment/tests/src/Functional/CommentNodeChangesTest.php
index 8229aefd5f5b1a6d071db492ecfd7f5e6dbd2312..0b9fddfd3dca6d2a2fead4d02adff1388e738274 100644
--- a/core/modules/comment/tests/src/Functional/CommentNodeChangesTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentNodeChangesTest.php
@@ -13,6 +13,11 @@
  */
 class CommentNodeChangesTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that comments are deleted with the node.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentNonNodeTest.php b/core/modules/comment/tests/src/Functional/CommentNonNodeTest.php
index ceae6f33668ddd4a8653bbe658fb5385bdcd267c..a543510062fa54836ca5eb52e0010b681764f3bd 100644
--- a/core/modules/comment/tests/src/Functional/CommentNonNodeTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentNonNodeTest.php
@@ -28,6 +28,11 @@ class CommentNonNodeTest extends BrowserTestBase {
 
   public static $modules = ['comment', 'user', 'field_ui', 'entity_test', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * An administrative user with permission to configure comment settings.
    *
diff --git a/core/modules/comment/tests/src/Functional/CommentPagerTest.php b/core/modules/comment/tests/src/Functional/CommentPagerTest.php
index 56adbf7a81dc00aceb6e3be15b276248d66de7d2..25da658ad6506ad3e59c526401960833bc265590 100644
--- a/core/modules/comment/tests/src/Functional/CommentPagerTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentPagerTest.php
@@ -13,6 +13,11 @@
  */
 class CommentPagerTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Confirms comment paging works correctly with flat and threaded comments.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentRssTest.php b/core/modules/comment/tests/src/Functional/CommentRssTest.php
index 33122dd2cd72b53f20d7aa8c4d4c74beb3f9ee75..0ae74e92d27a7ee0a50d41861c98eb9abb533e24 100644
--- a/core/modules/comment/tests/src/Functional/CommentRssTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentRssTest.php
@@ -23,6 +23,11 @@ class CommentRssTest extends CommentTestBase {
    */
   public static $modules = ['views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentStatisticsTest.php b/core/modules/comment/tests/src/Functional/CommentStatisticsTest.php
index 57b7ce24011db19f1a53917dc9cf7ef096a2c53f..eb84b24994c9cf11545316dc2e38b67cb0a867af 100644
--- a/core/modules/comment/tests/src/Functional/CommentStatisticsTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentStatisticsTest.php
@@ -20,6 +20,11 @@ class CommentStatisticsTest extends CommentTestBase {
    */
   protected $webUser2;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/comment/tests/src/Functional/CommentStatusFieldAccessTest.php b/core/modules/comment/tests/src/Functional/CommentStatusFieldAccessTest.php
index d2495d3791c75032378f0a16d117a25a7ee15daa..7009ea2c33e2faca24ebea63dd5067524b10a3a8 100644
--- a/core/modules/comment/tests/src/Functional/CommentStatusFieldAccessTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentStatusFieldAccessTest.php
@@ -20,6 +20,11 @@ class CommentStatusFieldAccessTest extends BrowserTestBase {
    */
   public $profile = 'testing';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Comment admin.
    *
diff --git a/core/modules/comment/tests/src/Functional/CommentThreadingTest.php b/core/modules/comment/tests/src/Functional/CommentThreadingTest.php
index 2e2b6868f6eb5b702ba8dd325cf90dff7c9b103c..50217d38c130fcfafc46ae66ac9f725101356bb9 100644
--- a/core/modules/comment/tests/src/Functional/CommentThreadingTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentThreadingTest.php
@@ -12,6 +12,11 @@
  */
 class CommentThreadingTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests the comment threading.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentTitleTest.php b/core/modules/comment/tests/src/Functional/CommentTitleTest.php
index ecf760abce6ec264dc67ed6c37cbe5b88b1d3290..b87b14d34d804cd75809652caab4059e51885dcf 100644
--- a/core/modules/comment/tests/src/Functional/CommentTitleTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentTitleTest.php
@@ -10,6 +10,11 @@
  */
 class CommentTitleTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests markup for comments with empty titles.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentTokenReplaceTest.php b/core/modules/comment/tests/src/Functional/CommentTokenReplaceTest.php
index 32670f5f19784903cf8c338db20f959bfae295e4..b402da57f851b3eeecbd012e6a1ed4df2f4950e0 100644
--- a/core/modules/comment/tests/src/Functional/CommentTokenReplaceTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentTokenReplaceTest.php
@@ -26,6 +26,11 @@ class CommentTokenReplaceTest extends CommentTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Creates a comment, then tests the tokens generated from it.
    */
diff --git a/core/modules/comment/tests/src/Functional/CommentTranslationUITest.php b/core/modules/comment/tests/src/Functional/CommentTranslationUITest.php
index b6bb692d47cd738280aa51d2a02e98e4f7c08dcf..8f47909403faf29508626f7741e3d9e9f167d193 100644
--- a/core/modules/comment/tests/src/Functional/CommentTranslationUITest.php
+++ b/core/modules/comment/tests/src/Functional/CommentTranslationUITest.php
@@ -16,6 +16,11 @@ class CommentTranslationUITest extends ContentTranslationUITestBase {
 
   use CommentTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The subject of the test comment.
    *
diff --git a/core/modules/comment/tests/src/Functional/CommentTypeTest.php b/core/modules/comment/tests/src/Functional/CommentTypeTest.php
index c2eeb928cf84d6a4d21d23f9a599d77af9952511..e13b2f59898ed29ed9bcd9a37dfd65c95fed655f 100644
--- a/core/modules/comment/tests/src/Functional/CommentTypeTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentTypeTest.php
@@ -17,6 +17,11 @@
  */
 class CommentTypeTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Admin user.
    *
diff --git a/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonAnonTest.php b/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonAnonTest.php
index 723df956012adb77a0852f8d15b772ed5c73e623..01e069623e134bf2a6975df4b7845f7beeee7e28 100644
--- a/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonAnonTest.php
+++ b/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonAnonTest.php
@@ -11,6 +11,11 @@ class CommentHalJsonAnonTest extends CommentHalJsonTestBase {
 
   use AnonResourceTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonBasicAuthTest.php b/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonBasicAuthTest.php
index 7d766fdfcacc28a388b5ac1784b788619150d93c..0062fe5a406906706f241f31e2a9c8a716e4ac2e 100644
--- a/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonBasicAuthTest.php
+++ b/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class CommentHalJsonBasicAuthTest extends CommentHalJsonTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonCookieTest.php b/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonCookieTest.php
index 806cf3fdcc967a9fc3ef44f2fd4297a8307a72c4..dd67cf6f2b7f597dae08d87c9fc7898bd5a27f17 100644
--- a/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonCookieTest.php
+++ b/core/modules/comment/tests/src/Functional/Hal/CommentHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class CommentHalJsonCookieTest extends CommentHalJsonTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonAnonTest.php b/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonAnonTest.php
index 179ae1861218ee305f935079c5eda9966c23d2a2..b3a254f8c1328db04a3ff3b24f554ec827b43f8b 100644
--- a/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonAnonTest.php
+++ b/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class CommentTypeHalJsonAnonTest extends CommentTypeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonBasicAuthTest.php b/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonBasicAuthTest.php
index 3a014bd1d19f98e7a5dc3c171b8fbd41edc78cd4..ff21f3489c7cceaee289a83342d805e7fcf467f9 100644
--- a/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonBasicAuthTest.php
+++ b/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class CommentTypeHalJsonBasicAuthTest extends CommentTypeResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonCookieTest.php b/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonCookieTest.php
index 9d6440ead469dd225a1756c7b16290c62f8e1359..0abdeefb67b8144774bf474f22ff17a2aefc9ff7 100644
--- a/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonCookieTest.php
+++ b/core/modules/comment/tests/src/Functional/Hal/CommentTypeHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class CommentTypeHalJsonCookieTest extends CommentTypeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentJsonAnonTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentJsonAnonTest.php
index 54925dd98374281dbbcb5f4d4bc6631a36b6a517..8c54ec12863b93c88bf0bfcb250ab6ed28268872 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentJsonAnonTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentJsonAnonTest.php
@@ -21,6 +21,11 @@ class CommentJsonAnonTest extends CommentResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentJsonBasicAuthTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentJsonBasicAuthTest.php
index a4f72551a47be55ad8ef59c67c5235e10e0d27a4..92d16fb4b188f60307c54677964c603ca5fcdb0d 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentJsonBasicAuthTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class CommentJsonBasicAuthTest extends CommentResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentJsonCookieTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentJsonCookieTest.php
index f2c78a25a257fcd87523a045ec4b65172a9e2eeb..846335acc3eb963c42f3d9d0353007c30b0c9cda 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentJsonCookieTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentJsonCookieTest.php
@@ -26,4 +26,9 @@ class CommentJsonCookieTest extends CommentResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonAnonTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonAnonTest.php
index 496e20aa60215af71a6880190dbb0748b3be4293..fd7f14000d05eee0a537a352bace6634f18b6ed9 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonAnonTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonAnonTest.php
@@ -21,4 +21,9 @@ class CommentTypeJsonAnonTest extends CommentTypeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonBasicAuthTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonBasicAuthTest.php
index c947dbc92c615f08d0bbd8b713b91002fba4d052..14fb9c9a050b3bf46f894c5119b46412da4a84e3 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonBasicAuthTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class CommentTypeJsonBasicAuthTest extends CommentTypeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonCookieTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonCookieTest.php
index ddbdf27ccb2bdddc1bd82274d130f31b4fcc91d3..4fe56f1d4fa1158ac98d24df2f41ae7327df0e0e 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonCookieTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentTypeJsonCookieTest.php
@@ -26,4 +26,9 @@ class CommentTypeJsonCookieTest extends CommentTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlAnonTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlAnonTest.php
index 96d6c41a0edbe3745cb65e52e590caabf754cba1..fed57acaacbe150c1630f9e8e4e17275389615fd 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlAnonTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlAnonTest.php
@@ -23,4 +23,9 @@ class CommentTypeXmlAnonTest extends CommentTypeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlBasicAuthTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlBasicAuthTest.php
index e92f2bcc65daed830ddc687d57580f975a926724..a1fc840eec4ea303ac46e6bdcebae026e75f826d 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlBasicAuthTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class CommentTypeXmlBasicAuthTest extends CommentTypeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlCookieTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlCookieTest.php
index 01f42db448da9d34a1b0739d76f13339929de4af..fa16de1a45a47b93a442a6e78caea5ba426666c3 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlCookieTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentTypeXmlCookieTest.php
@@ -28,4 +28,9 @@ class CommentTypeXmlCookieTest extends CommentTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentXmlAnonTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentXmlAnonTest.php
index 22c1b858f5e35a75345f91010085cb36253e6dd1..1950cbabf37595f0b363e67f1fde87a0d1f3b654 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentXmlAnonTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentXmlAnonTest.php
@@ -23,6 +23,11 @@ class CommentXmlAnonTest extends CommentResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentXmlBasicAuthTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentXmlBasicAuthTest.php
index d1f38e44a4b3fcefad436784c98cfdbbf5405ccd..90f4eacdd64e65d346d18eb718436d353e496477 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentXmlBasicAuthTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class CommentXmlBasicAuthTest extends CommentResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Rest/CommentXmlCookieTest.php b/core/modules/comment/tests/src/Functional/Rest/CommentXmlCookieTest.php
index e06cf2652183e9e3545a9241adba01b15badab5d..57631e1880f1cf3d5c9e8a5a2b3c85401743c4e7 100644
--- a/core/modules/comment/tests/src/Functional/Rest/CommentXmlCookieTest.php
+++ b/core/modules/comment/tests/src/Functional/Rest/CommentXmlCookieTest.php
@@ -28,6 +28,11 @@ class CommentXmlCookieTest extends CommentResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Views/CommentAdminTest.php b/core/modules/comment/tests/src/Functional/Views/CommentAdminTest.php
index ee42dcaddd07ca30e618634c2a0b2d6e8ad654ed..a31ad265926af4556bfdb9bbee04c6dbdece67d0 100644
--- a/core/modules/comment/tests/src/Functional/Views/CommentAdminTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/CommentAdminTest.php
@@ -20,6 +20,11 @@
  */
 class CommentAdminTest extends CommentBrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/comment/tests/src/Functional/Views/CommentFieldFilterTest.php b/core/modules/comment/tests/src/Functional/Views/CommentFieldFilterTest.php
index dabacc3bed2545cb1fb44ec4d36564eda4a73481..18bfde335434255d1953870d61d923d38fb1768f 100644
--- a/core/modules/comment/tests/src/Functional/Views/CommentFieldFilterTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/CommentFieldFilterTest.php
@@ -17,6 +17,11 @@ class CommentFieldFilterTest extends CommentTestBase {
    */
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/comment/tests/src/Functional/Views/CommentOperationsTest.php b/core/modules/comment/tests/src/Functional/Views/CommentOperationsTest.php
index 4bef37edc2d46f6be345be128621888d5cdb85b0..ecd15d2a97ff355eae858a5e2c71e85d68ea1e06 100644
--- a/core/modules/comment/tests/src/Functional/Views/CommentOperationsTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/CommentOperationsTest.php
@@ -16,6 +16,11 @@ class CommentOperationsTest extends CommentTestBase {
    */
   public static $testViews = ['test_comment_operations'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Test the operations field plugin.
    */
diff --git a/core/modules/comment/tests/src/Functional/Views/CommentRestExportTest.php b/core/modules/comment/tests/src/Functional/Views/CommentRestExportTest.php
index 908a86a3592e94dc4c225db514c44e2182fcfd25..d5046a396ed9e7a6292e647201eda9c55cffd6c3 100644
--- a/core/modules/comment/tests/src/Functional/Views/CommentRestExportTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/CommentRestExportTest.php
@@ -12,6 +12,11 @@
  */
 class CommentRestExportTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/comment/tests/src/Functional/Views/CommentRowTest.php b/core/modules/comment/tests/src/Functional/Views/CommentRowTest.php
index 7cf3ef3b241661a7d66bd8197049dfcb839db2bd..8cf2121a5eac4f43aae08b07967ff7920154d5d7 100644
--- a/core/modules/comment/tests/src/Functional/Views/CommentRowTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/CommentRowTest.php
@@ -9,6 +9,11 @@
  */
 class CommentRowTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/comment/tests/src/Functional/Views/DefaultViewRecentCommentsTest.php b/core/modules/comment/tests/src/Functional/Views/DefaultViewRecentCommentsTest.php
index 9ba4d85e77d652c11827dbe35e2a21a38e25aade..b6f98a0dd23a39fcfbdc2a3abc18ad4ce03461c9 100644
--- a/core/modules/comment/tests/src/Functional/Views/DefaultViewRecentCommentsTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/DefaultViewRecentCommentsTest.php
@@ -25,6 +25,11 @@ class DefaultViewRecentCommentsTest extends ViewTestBase {
    */
   public static $modules = ['node', 'comment', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Number of results for the Master display.
    *
diff --git a/core/modules/comment/tests/src/Functional/Views/NodeCommentsTest.php b/core/modules/comment/tests/src/Functional/Views/NodeCommentsTest.php
index e2c5d15ef51f03792822fa175ec67146572836b7..02c91f4ed5d6aeec223b5ccca58c0723fd82171e 100644
--- a/core/modules/comment/tests/src/Functional/Views/NodeCommentsTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/NodeCommentsTest.php
@@ -16,6 +16,11 @@ class NodeCommentsTest extends CommentTestBase {
    */
   public static $modules = ['history'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/comment/tests/src/Functional/Views/RowRssTest.php b/core/modules/comment/tests/src/Functional/Views/RowRssTest.php
index 7d61852ef8b65a9590563a0ecb7478e773b770cc..f8a24afa4e8706f573733f7fa9cf367576bebf6e 100644
--- a/core/modules/comment/tests/src/Functional/Views/RowRssTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/RowRssTest.php
@@ -10,6 +10,11 @@
  */
 class RowRssTest extends CommentTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/comment/tests/src/Functional/Views/WizardTest.php b/core/modules/comment/tests/src/Functional/Views/WizardTest.php
index 73332a87dfd180c2b139acd438f3561563d1e29b..6ae5c11270073fd69e85f86c504612b3812fdded 100644
--- a/core/modules/comment/tests/src/Functional/Views/WizardTest.php
+++ b/core/modules/comment/tests/src/Functional/Views/WizardTest.php
@@ -23,6 +23,11 @@ class WizardTest extends WizardTestBase {
    */
   public static $modules = ['node', 'comment'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonAnonTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonAnonTest.php
index d874f45f263c3f874e4ad26b2b6310e460bb0728..8e20d7259115d876fc4cd8ae36b4235727000dfc 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonAnonTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ConfigTestHalJsonAnonTest extends ConfigTestResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonBasicAuthTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonBasicAuthTest.php
index 01a69c329d8b3310dc7321196b39fdff5f724a96..f8adc1d563fde77d2d2727a4a9b17b2e4daa2aaf 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonBasicAuthTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class ConfigTestHalJsonBasicAuthTest extends ConfigTestResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonCookieTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonCookieTest.php
index eb670d2a4ef7b351141f00b5907781cba9ab9d55..a0f8dc1f3c204e9f6e8d5722cc240313873bbb19 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonCookieTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Hal/ConfigTestHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ConfigTestHalJsonCookieTest extends ConfigTestResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonAnonTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonAnonTest.php
index 0121b1f3a4c4331d9372acde2ee8fd34c002e159..e284f9dad275e1cd9f02a20554bea5e53f60a026 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonAnonTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonAnonTest.php
@@ -21,4 +21,9 @@ class ConfigTestJsonAnonTest extends ConfigTestResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonBasicAuthTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonBasicAuthTest.php
index 87c415840a1db6eb77eb50ab1e8e3d833d5e8e39..724effcc9ab1ac468f0fdee79cb9ba2b056cab5a 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonBasicAuthTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ConfigTestJsonBasicAuthTest extends ConfigTestResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonCookieTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonCookieTest.php
index 173d7613325d856e16e9477c5a97f7b6d434f879..97efc5852a2259edc270b8eedab0c92b84120437 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonCookieTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestJsonCookieTest.php
@@ -26,4 +26,9 @@ class ConfigTestJsonCookieTest extends ConfigTestResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlAnonTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlAnonTest.php
index 451e86df22444ed1f68d322d7eaf670ed11a94a0..05c1341903fcb3c8b5c554397d07ad33d6ac9a23 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlAnonTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlAnonTest.php
@@ -23,4 +23,9 @@ class ConfigTestXmlAnonTest extends ConfigTestResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlBasicAuthTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlBasicAuthTest.php
index c65028f212badaca7bb60567a0569471db7ef911..f253c383472e072cb980721519e9765a58ccaa88 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlBasicAuthTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ConfigTestXmlBasicAuthTest extends ConfigTestResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlCookieTest.php b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlCookieTest.php
index 540b14e8d36b315ea73d8b55b1e3ab3ca35c4418..3be09e2e7843afb45aae8d1cbd8b13c7b2f65793 100644
--- a/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlCookieTest.php
+++ b/core/modules/config/tests/config_test/tests/src/Functional/Rest/ConfigTestXmlCookieTest.php
@@ -28,4 +28,9 @@ class ConfigTestXmlCookieTest extends ConfigTestResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/config/tests/src/Functional/CacheabilityMetadataConfigOverrideIntegrationTest.php b/core/modules/config/tests/src/Functional/CacheabilityMetadataConfigOverrideIntegrationTest.php
index 433d288e51febf4b0e6e31318b65c6d8155f8a59..496dbbc874ee1cd2262d334507751941f74f790c 100644
--- a/core/modules/config/tests/src/Functional/CacheabilityMetadataConfigOverrideIntegrationTest.php
+++ b/core/modules/config/tests/src/Functional/CacheabilityMetadataConfigOverrideIntegrationTest.php
@@ -22,6 +22,11 @@ class CacheabilityMetadataConfigOverrideIntegrationTest extends BrowserTestBase
     'config_override_integration_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigDependencyWebTest.php b/core/modules/config/tests/src/Functional/ConfigDependencyWebTest.php
index 8c8637bda78f55f9e17235e37d3909b406ff5ba7..8866d67e1d7e138e47e3a1d1127865c29415be71 100644
--- a/core/modules/config/tests/src/Functional/ConfigDependencyWebTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigDependencyWebTest.php
@@ -24,6 +24,11 @@ class ConfigDependencyWebTest extends BrowserTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests ConfigDependencyDeleteFormTrait.
    *
diff --git a/core/modules/config/tests/src/Functional/ConfigDraggableListBuilderTest.php b/core/modules/config/tests/src/Functional/ConfigDraggableListBuilderTest.php
index 74829359a108620222279601ecf4af7c3c0e9521..a9effb4b0fcf4369816e64b02a5c8635bb9fccda 100644
--- a/core/modules/config/tests/src/Functional/ConfigDraggableListBuilderTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigDraggableListBuilderTest.php
@@ -17,6 +17,11 @@ class ConfigDraggableListBuilderTest extends BrowserTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test draggable lists.
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigEntityFormOverrideTest.php b/core/modules/config/tests/src/Functional/ConfigEntityFormOverrideTest.php
index 27610616dd89ea3dc80ed1d5d4efc570a7ff9e9f..628fb4bf826d043b03d4bd27d949e687ec9d175a 100644
--- a/core/modules/config/tests/src/Functional/ConfigEntityFormOverrideTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigEntityFormOverrideTest.php
@@ -16,6 +16,11 @@ class ConfigEntityFormOverrideTest extends BrowserTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that overrides do not affect forms or listing screens.
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigEntityListMultilingualTest.php b/core/modules/config/tests/src/Functional/ConfigEntityListMultilingualTest.php
index cf9ff99f221efbad4c217b8e35e1dcc954b761a1..882190a9c063b0eb6e8e04088c22fc00ce5a33ac 100644
--- a/core/modules/config/tests/src/Functional/ConfigEntityListMultilingualTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigEntityListMultilingualTest.php
@@ -19,6 +19,11 @@ class ConfigEntityListMultilingualTest extends BrowserTestBase {
    */
   public static $modules = ['config_test', 'language', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigEntityListTest.php b/core/modules/config/tests/src/Functional/ConfigEntityListTest.php
index ec8f88aa5db49b1b6f33379e598c7c265d76f1b9..673223f494f6bb99bca623c759a2820f8130688a 100644
--- a/core/modules/config/tests/src/Functional/ConfigEntityListTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigEntityListTest.php
@@ -23,6 +23,11 @@ class ConfigEntityListTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigEntityStatusUITest.php b/core/modules/config/tests/src/Functional/ConfigEntityStatusUITest.php
index b0fa22f2dec9e1a2e23e2fec703d3082b3c46f58..c987551449b1271566a3f0336b1d50b275588c84 100644
--- a/core/modules/config/tests/src/Functional/ConfigEntityStatusUITest.php
+++ b/core/modules/config/tests/src/Functional/ConfigEntityStatusUITest.php
@@ -18,6 +18,11 @@ class ConfigEntityStatusUITest extends BrowserTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests status operations.
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigEntityTest.php b/core/modules/config/tests/src/Functional/ConfigEntityTest.php
index e18d2cdfce02495f8a3b42dbc1abd8759518659a..2606ae8b92b25d0a8290ee4caf4eeefd4db59ce2 100644
--- a/core/modules/config/tests/src/Functional/ConfigEntityTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigEntityTest.php
@@ -29,6 +29,11 @@ class ConfigEntityTest extends BrowserTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests CRUD operations.
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigExportImportUITest.php b/core/modules/config/tests/src/Functional/ConfigExportImportUITest.php
index 4e20768ab35ab4d005a22eac3a5a8b89f7e3cde7..9a6c3525be96a5081b50b0bbf9c1e8f676b1d851 100644
--- a/core/modules/config/tests/src/Functional/ConfigExportImportUITest.php
+++ b/core/modules/config/tests/src/Functional/ConfigExportImportUITest.php
@@ -68,6 +68,11 @@ class ConfigExportImportUITest extends BrowserTestBase {
    */
   public static $modules = ['config', 'node', 'field'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigExportUITest.php b/core/modules/config/tests/src/Functional/ConfigExportUITest.php
index 215b582bf6459dfa18dd0113cd6a45db3ec5efde..ba88e6d2d1ae7891146b08fd8eaf1da43b9d1aa7 100644
--- a/core/modules/config/tests/src/Functional/ConfigExportUITest.php
+++ b/core/modules/config/tests/src/Functional/ConfigExportUITest.php
@@ -21,6 +21,11 @@ class ConfigExportUITest extends BrowserTestBase {
    */
   public static $modules = ['config', 'config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigFormOverrideTest.php b/core/modules/config/tests/src/Functional/ConfigFormOverrideTest.php
index 3bba16daa75c4b7027dbf67890c38abbf452a409..14edd8838685611e1e621ae02ed7a8cded636ff7 100644
--- a/core/modules/config/tests/src/Functional/ConfigFormOverrideTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigFormOverrideTest.php
@@ -12,6 +12,11 @@
  */
 class ConfigFormOverrideTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that overrides do not affect forms.
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigImportInstallProfileTest.php b/core/modules/config/tests/src/Functional/ConfigImportInstallProfileTest.php
index 8b0787d6ee02ef6ca2b862ec0267d5592c3d23e2..66bf8a9a6aff4950f9303551f01c752653148dfa 100644
--- a/core/modules/config/tests/src/Functional/ConfigImportInstallProfileTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigImportInstallProfileTest.php
@@ -25,6 +25,11 @@ class ConfigImportInstallProfileTest extends BrowserTestBase {
    */
   public static $modules = ['config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with the 'synchronize configuration' permission.
    *
diff --git a/core/modules/config/tests/src/Functional/ConfigImportUITest.php b/core/modules/config/tests/src/Functional/ConfigImportUITest.php
index 3786b5155750753612e8ab4f8389757537fb8e3a..bcad9eeb6661ff7290670696731478976587d3b9 100644
--- a/core/modules/config/tests/src/Functional/ConfigImportUITest.php
+++ b/core/modules/config/tests/src/Functional/ConfigImportUITest.php
@@ -21,6 +21,11 @@ class ConfigImportUITest extends BrowserTestBase {
    */
   public static $modules = ['config', 'config_test', 'config_import_test', 'text', 'options'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with the 'synchronize configuration' permission.
    *
diff --git a/core/modules/config/tests/src/Functional/ConfigImportUploadTest.php b/core/modules/config/tests/src/Functional/ConfigImportUploadTest.php
index bc4dc7c5c32a89fff9602dbb59c19a050930924d..ed62bd12e9b8270cdff3bc00ab72683f7d94d390 100644
--- a/core/modules/config/tests/src/Functional/ConfigImportUploadTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigImportUploadTest.php
@@ -29,6 +29,11 @@ class ConfigImportUploadTest extends BrowserTestBase {
    */
   public static $modules = ['config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/config/tests/src/Functional/ConfigInstallProfileOverrideTest.php b/core/modules/config/tests/src/Functional/ConfigInstallProfileOverrideTest.php
index 3a151b574dd64f5b048dc5b1a76f20ac26426149..80a6861b330529d5aa2c52398bad2e3a2bd48a05 100644
--- a/core/modules/config/tests/src/Functional/ConfigInstallProfileOverrideTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigInstallProfileOverrideTest.php
@@ -26,6 +26,11 @@ class ConfigInstallProfileOverrideTest extends BrowserTestBase {
    */
   protected $profile = 'testing_config_overrides';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests install profile config changes.
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigInstallProfileUnmetDependenciesTest.php b/core/modules/config/tests/src/Functional/ConfigInstallProfileUnmetDependenciesTest.php
index 59f9f706ee70595e3ffc3b37dc2294a8054ad99a..b9ae7bc5c94e037d5b11a116d9ab3d54a779ae5f 100644
--- a/core/modules/config/tests/src/Functional/ConfigInstallProfileUnmetDependenciesTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigInstallProfileUnmetDependenciesTest.php
@@ -27,6 +27,11 @@ class ConfigInstallProfileUnmetDependenciesTest extends InstallerTestBase {
    */
   protected $expectedException = FALSE;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigInstallWebTest.php b/core/modules/config/tests/src/Functional/ConfigInstallWebTest.php
index 5f7c87d013780a845e4c0a56c988e4671fea4e72..1496beeb2de72839b813043cf96349e760be68a3 100644
--- a/core/modules/config/tests/src/Functional/ConfigInstallWebTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigInstallWebTest.php
@@ -22,6 +22,11 @@ class ConfigInstallWebTest extends BrowserTestBase {
    */
   protected $adminUser;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigLanguageOverrideWebTest.php b/core/modules/config/tests/src/Functional/ConfigLanguageOverrideWebTest.php
index c7e0b27d444832de8566d0d6b272ed573255258c..b67d2b9400ab108bfd05740b6a55bf389756a4d6 100644
--- a/core/modules/config/tests/src/Functional/ConfigLanguageOverrideWebTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigLanguageOverrideWebTest.php
@@ -24,6 +24,11 @@ class ConfigLanguageOverrideWebTest extends BrowserTestBase {
     'system',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigOtherModuleTest.php b/core/modules/config/tests/src/Functional/ConfigOtherModuleTest.php
index 4ff2b18f80bcf2f4fa4f9f09a289fc9cca50933e..d44baf7e8234dd37a75cc3ec54eff5c602bece80 100644
--- a/core/modules/config/tests/src/Functional/ConfigOtherModuleTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigOtherModuleTest.php
@@ -11,6 +11,11 @@
  */
 class ConfigOtherModuleTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests enabling the provider of the default configuration first.
    */
diff --git a/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php b/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php
index 8c5491b0b6fa0924c76efc5fb27ee8623bb4e332..c80af8d9e6b97565ffff994531433a2e7b661efb 100644
--- a/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php
+++ b/core/modules/config/tests/src/Functional/ConfigSingleImportExportTest.php
@@ -26,6 +26,11 @@ class ConfigSingleImportExportTest extends BrowserTestBase {
     'language',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/config/tests/src/Functional/LanguageNegotiationFormOverrideTest.php b/core/modules/config/tests/src/Functional/LanguageNegotiationFormOverrideTest.php
index 6c4e1bb3118a51e118ae9077a28c9e253dc198ca..0aa15ea1ea3828d707cea65664a2c81213093a2f 100644
--- a/core/modules/config/tests/src/Functional/LanguageNegotiationFormOverrideTest.php
+++ b/core/modules/config/tests/src/Functional/LanguageNegotiationFormOverrideTest.php
@@ -14,6 +14,11 @@ class LanguageNegotiationFormOverrideTest extends BrowserTestBase {
 
   public static $modules = ['language', 'locale', 'locale_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that overrides do not affect language-negotiation form values.
    */
diff --git a/core/modules/config/tests/src/Functional/SchemaConfigListenerWebTest.php b/core/modules/config/tests/src/Functional/SchemaConfigListenerWebTest.php
index 6d221e26ddc127c4695cb3ee33ef7aff6850f5de..588db76a331e34473579d364da8d17046e597025 100644
--- a/core/modules/config/tests/src/Functional/SchemaConfigListenerWebTest.php
+++ b/core/modules/config/tests/src/Functional/SchemaConfigListenerWebTest.php
@@ -17,6 +17,11 @@ class SchemaConfigListenerWebTest extends BrowserTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests \Drupal\Core\Config\Development\ConfigSchemaChecker.
    */
diff --git a/core/modules/config/tests/src/Functional/TransformedConfigExportImportUITest.php b/core/modules/config/tests/src/Functional/TransformedConfigExportImportUITest.php
index b87d12a16dc4cceac5b872ccbc33e6f418cb606a..ce7f160d58ba80322006ea0d0958fe6d1aa6d5fa 100644
--- a/core/modules/config/tests/src/Functional/TransformedConfigExportImportUITest.php
+++ b/core/modules/config/tests/src/Functional/TransformedConfigExportImportUITest.php
@@ -20,6 +20,11 @@ class TransformedConfigExportImportUITest extends BrowserTestBase {
     'config_transformer_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/config/tests/src/FunctionalJavascript/ConfigEntityTest.php b/core/modules/config/tests/src/FunctionalJavascript/ConfigEntityTest.php
index f7e6dc8ff528caec5927a5cfe67f810809a06325..7ea62e2e90f114e011571561787451b8a335d586 100644
--- a/core/modules/config/tests/src/FunctionalJavascript/ConfigEntityTest.php
+++ b/core/modules/config/tests/src/FunctionalJavascript/ConfigEntityTest.php
@@ -16,6 +16,11 @@ class ConfigEntityTest extends WebDriverTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests ajax operations through the UI on 'Add' page.
    */
diff --git a/core/modules/config_translation/tests/src/Functional/ConfigTranslationCacheTest.php b/core/modules/config_translation/tests/src/Functional/ConfigTranslationCacheTest.php
index 0def24a490b412773951b55c3bf88a2e78edbeb8..7b64987605c402ea30a99b7831444a10ab1556b9 100644
--- a/core/modules/config_translation/tests/src/Functional/ConfigTranslationCacheTest.php
+++ b/core/modules/config_translation/tests/src/Functional/ConfigTranslationCacheTest.php
@@ -37,6 +37,11 @@ class ConfigTranslationCacheTest extends BrowserTestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Languages to enable.
    *
diff --git a/core/modules/config_translation/tests/src/Functional/ConfigTranslationDateFormatUiTest.php b/core/modules/config_translation/tests/src/Functional/ConfigTranslationDateFormatUiTest.php
index 7cbeb57746a73a87b7d6961503bb5732416f7cd0..c0c88738510dc16ff1be059630e9d38082c6343e 100644
--- a/core/modules/config_translation/tests/src/Functional/ConfigTranslationDateFormatUiTest.php
+++ b/core/modules/config_translation/tests/src/Functional/ConfigTranslationDateFormatUiTest.php
@@ -18,6 +18,11 @@ class ConfigTranslationDateFormatUiTest extends BrowserTestBase {
     'system',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/config_translation/tests/src/Functional/ConfigTranslationListUiTest.php b/core/modules/config_translation/tests/src/Functional/ConfigTranslationListUiTest.php
index 1d0116dc99973741160c60a13f45f9d28764d9a4..7b1ca0ef86ab360a564e0314093233e64887468c 100644
--- a/core/modules/config_translation/tests/src/Functional/ConfigTranslationListUiTest.php
+++ b/core/modules/config_translation/tests/src/Functional/ConfigTranslationListUiTest.php
@@ -41,6 +41,11 @@ class ConfigTranslationListUiTest extends BrowserTestBase {
     'toolbar',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Admin user with all needed permissions.
    *
diff --git a/core/modules/config_translation/tests/src/Functional/ConfigTranslationOverviewTest.php b/core/modules/config_translation/tests/src/Functional/ConfigTranslationOverviewTest.php
index 45f6636b37cdb7bd9ad13cbdc66440db5baec656..d5647d45a411c0486c473a029586b33fc036938d 100644
--- a/core/modules/config_translation/tests/src/Functional/ConfigTranslationOverviewTest.php
+++ b/core/modules/config_translation/tests/src/Functional/ConfigTranslationOverviewTest.php
@@ -30,6 +30,11 @@ class ConfigTranslationOverviewTest extends BrowserTestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Languages to enable.
    *
diff --git a/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiTest.php b/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiTest.php
index 748a9ecabfb0a77589ce7b007535bd074191e372..bb5e218191a6ba0c5df9fd2f7108480f89abc0fe 100644
--- a/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiTest.php
+++ b/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiTest.php
@@ -46,6 +46,11 @@ class ConfigTranslationUiTest extends BrowserTestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Languages to enable.
    *
diff --git a/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiThemeTest.php b/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiThemeTest.php
index dcfb7916fe850d1724e37e531d47b477097b679c..6754420c1c574e6b9149c6c69654a7eadf7bd76d 100644
--- a/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiThemeTest.php
+++ b/core/modules/config_translation/tests/src/Functional/ConfigTranslationUiThemeTest.php
@@ -19,6 +19,11 @@ class ConfigTranslationUiThemeTest extends BrowserTestBase {
    */
   public static $modules = ['config_translation', 'config_translation_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Languages to enable.
    *
diff --git a/core/modules/config_translation/tests/src/Functional/ConfigTranslationViewListUiTest.php b/core/modules/config_translation/tests/src/Functional/ConfigTranslationViewListUiTest.php
index edb41f9ad44190537af4920317c92fdd14a7eba3..230ffd3aaa0c9ed4bb211310c35154daa92326a9 100644
--- a/core/modules/config_translation/tests/src/Functional/ConfigTranslationViewListUiTest.php
+++ b/core/modules/config_translation/tests/src/Functional/ConfigTranslationViewListUiTest.php
@@ -25,6 +25,11 @@ class ConfigTranslationViewListUiTest extends UITestBase {
    */
   public static $modules = ['config_translation', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/config_translation/tests/src/FunctionalJavascript/ConfigTranslationUiTest.php b/core/modules/config_translation/tests/src/FunctionalJavascript/ConfigTranslationUiTest.php
index 585d2d1d38d046cece76ad16237a53445f0a352f..0261663a460b8285f0c55a52520af8a1d95312a7 100644
--- a/core/modules/config_translation/tests/src/FunctionalJavascript/ConfigTranslationUiTest.php
+++ b/core/modules/config_translation/tests/src/FunctionalJavascript/ConfigTranslationUiTest.php
@@ -22,6 +22,11 @@ class ConfigTranslationUiTest extends WebDriverTestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that contextual link related to views.
    */
diff --git a/core/modules/contact/tests/src/Functional/ContactLanguageTest.php b/core/modules/contact/tests/src/Functional/ContactLanguageTest.php
index 0c34884503c166b32a295d680eab64cbacdf9549..2f08a9f40b9a84ea5cc7a507e768fa0082bce3f6 100644
--- a/core/modules/contact/tests/src/Functional/ContactLanguageTest.php
+++ b/core/modules/contact/tests/src/Functional/ContactLanguageTest.php
@@ -26,6 +26,11 @@ class ContactLanguageTest extends BrowserTestBase {
     'contact_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/ContactPersonalTest.php b/core/modules/contact/tests/src/Functional/ContactPersonalTest.php
index 2c8fae5b5a0a0045627312f2bf4e0fad62c412f9..680d1239db3131dd1ddfd390f1386a7f318e6248 100644
--- a/core/modules/contact/tests/src/Functional/ContactPersonalTest.php
+++ b/core/modules/contact/tests/src/Functional/ContactPersonalTest.php
@@ -27,6 +27,11 @@ class ContactPersonalTest extends BrowserTestBase {
    */
   public static $modules = ['contact', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with some administrative permissions.
    *
diff --git a/core/modules/contact/tests/src/Functional/ContactSitewideTest.php b/core/modules/contact/tests/src/Functional/ContactSitewideTest.php
index aef0aa657498df3a65008c1f5dcf2808722145f8..5093a545c5b3a71fef5c103b4bc9009236ddd78f 100644
--- a/core/modules/contact/tests/src/Functional/ContactSitewideTest.php
+++ b/core/modules/contact/tests/src/Functional/ContactSitewideTest.php
@@ -31,6 +31,11 @@ class ContactSitewideTest extends BrowserTestBase {
    */
   public static $modules = ['text', 'contact', 'field_ui', 'contact_test', 'block', 'error_service_test', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/ContactStorageTest.php b/core/modules/contact/tests/src/Functional/ContactStorageTest.php
index fbd938bb8a55d1e347bc3af6862174163a17aaa9..ac964f935362b4ca61518e6f87e75afb4fa6586e 100644
--- a/core/modules/contact/tests/src/Functional/ContactStorageTest.php
+++ b/core/modules/contact/tests/src/Functional/ContactStorageTest.php
@@ -31,6 +31,11 @@ class ContactStorageTest extends ContactSitewideTest {
     'contact_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests configuration options and the site-wide contact form.
    */
diff --git a/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonAnonTest.php b/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonAnonTest.php
index e863c978dd1f2f35b5b7a7acfc020d9c6ad10659..4a9babde3378b905963c6758d3987300de5c91f5 100644
--- a/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonAnonTest.php
+++ b/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ContactFormHalJsonAnonTest extends ContactFormResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonBasicAuthTest.php b/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonBasicAuthTest.php
index 7280cfdc7e905f4270cd7711af3c403716ae5fd9..36d867235fcf63a1cf908e12fe9016bf4cf3dfc1 100644
--- a/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonBasicAuthTest.php
+++ b/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class ContactFormHalJsonBasicAuthTest extends ContactFormResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonCookieTest.php b/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonCookieTest.php
index 2592ae761445c0592a6369f948f0dfe7902b79c5..d61e132a1abd6cbd4724f482e505984c09de29c7 100644
--- a/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonCookieTest.php
+++ b/core/modules/contact/tests/src/Functional/Hal/ContactFormHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ContactFormHalJsonCookieTest extends ContactFormResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonAnonTest.php b/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonAnonTest.php
index 088a872798bd51e019f06f82ab97bfa391ed4f28..a95841f29962280c186f5c782df6791a98c6540e 100644
--- a/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonAnonTest.php
+++ b/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonAnonTest.php
@@ -19,6 +19,11 @@ class MessageHalJsonAnonTest extends MessageResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonBasicAuthTest.php b/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonBasicAuthTest.php
index 363dbd7c87a8b9448995bf69b30049bf206394dd..4da136e45e9aebd2ed58ca6c07695e6048d356ac 100644
--- a/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonBasicAuthTest.php
+++ b/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class MessageHalJsonBasicAuthTest extends MessageHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonCookieTest.php b/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonCookieTest.php
index 0353cd2ea336dfecd8e9fc4685e4aa12916a0672..2d93a661c0fa946b1950c6032cdfce6b16568803 100644
--- a/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonCookieTest.php
+++ b/core/modules/contact/tests/src/Functional/Hal/MessageHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class MessageHalJsonCookieTest extends MessageHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonAnonTest.php b/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonAnonTest.php
index fecbf68870ef39e8fc191a365039dc4665b5c2e7..6f0eb31245907aaf5ec8144f27df6d89ffe60b19 100644
--- a/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonAnonTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonAnonTest.php
@@ -21,4 +21,9 @@ class ContactFormJsonAnonTest extends ContactFormResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonBasicAuthTest.php b/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonBasicAuthTest.php
index 8e92a91009b189b7307a5c952790e22449238e9b..f5047081bdb55ee1ea7b71923c3c86636ea4c5a0 100644
--- a/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonBasicAuthTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ContactFormJsonBasicAuthTest extends ContactFormResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonCookieTest.php b/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonCookieTest.php
index 6ba666043a2eaf7e463b4091a9ca0c3d08d818e6..076e370126a12043806ba75090275e1c6e839d9e 100644
--- a/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonCookieTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/ContactFormJsonCookieTest.php
@@ -26,4 +26,9 @@ class ContactFormJsonCookieTest extends ContactFormResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlAnonTest.php b/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlAnonTest.php
index 2931edda8d1a387556ad04aed584d8c2b45bf515..f538af9192f26a06e253ce7cdff9d1dc7ceae80a 100644
--- a/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlAnonTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlAnonTest.php
@@ -23,4 +23,9 @@ class ContactFormXmlAnonTest extends ContactFormResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlBasicAuthTest.php b/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlBasicAuthTest.php
index dfc4b6498a18f97365d2e63f00633a9ef71fae32..a2588c9f3b1d21b4849c922de9c09b0cebb0d4a5 100644
--- a/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlBasicAuthTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ContactFormXmlBasicAuthTest extends ContactFormResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlCookieTest.php b/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlCookieTest.php
index cdcd2daa3e51e18291ca1b0f52c425717f8ed219..3dde171d8188034112cd4bba196b2e7d3cda6e8e 100644
--- a/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlCookieTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/ContactFormXmlCookieTest.php
@@ -28,4 +28,9 @@ class ContactFormXmlCookieTest extends ContactFormResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/MessageJsonAnonTest.php b/core/modules/contact/tests/src/Functional/Rest/MessageJsonAnonTest.php
index a5b2954249ce2d1da600737a555246363032b7e7..fbd0bee0916e8d02c12aca8e16d3da41c08bcbbc 100644
--- a/core/modules/contact/tests/src/Functional/Rest/MessageJsonAnonTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/MessageJsonAnonTest.php
@@ -21,4 +21,9 @@ class MessageJsonAnonTest extends MessageResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/MessageJsonBasicAuthTest.php b/core/modules/contact/tests/src/Functional/Rest/MessageJsonBasicAuthTest.php
index f7f759ab9029d342eeebf5dc76954dccf8ec72a7..0d281630b078f758dfd903ff780fbcca16e456ed 100644
--- a/core/modules/contact/tests/src/Functional/Rest/MessageJsonBasicAuthTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/MessageJsonBasicAuthTest.php
@@ -26,6 +26,11 @@ class MessageJsonBasicAuthTest extends MessageResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Rest/MessageJsonCookieTest.php b/core/modules/contact/tests/src/Functional/Rest/MessageJsonCookieTest.php
index 0444a5a06a93ac8a7ba278d7918b3dfac3132c4a..e8fa8e8a312895cb4ae1a2e4932ba8e945a0b360 100644
--- a/core/modules/contact/tests/src/Functional/Rest/MessageJsonCookieTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/MessageJsonCookieTest.php
@@ -26,4 +26,9 @@ class MessageJsonCookieTest extends MessageResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/MessageXmlAnonTest.php b/core/modules/contact/tests/src/Functional/Rest/MessageXmlAnonTest.php
index 6b9b10de8a8df3ca26f49a238bcc3db19981c63b..51b327fd628f8c22b81a7b8a97e31e0cf252e278 100644
--- a/core/modules/contact/tests/src/Functional/Rest/MessageXmlAnonTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/MessageXmlAnonTest.php
@@ -23,4 +23,9 @@ class MessageXmlAnonTest extends MessageResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/contact/tests/src/Functional/Rest/MessageXmlBasicAuthTest.php b/core/modules/contact/tests/src/Functional/Rest/MessageXmlBasicAuthTest.php
index 152a94a86f2867bd53373b8eac41e83053e97915..64547a5a720a8f91bebd52d209ac93efe1ed3bf7 100644
--- a/core/modules/contact/tests/src/Functional/Rest/MessageXmlBasicAuthTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/MessageXmlBasicAuthTest.php
@@ -28,6 +28,11 @@ class MessageXmlBasicAuthTest extends MessageResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Rest/MessageXmlCookieTest.php b/core/modules/contact/tests/src/Functional/Rest/MessageXmlCookieTest.php
index ecdf0dba55c0e4f56155e2c1bf82034628de7bea..6bc53fec53a4a8b65222847093100ae88c4dd32f 100644
--- a/core/modules/contact/tests/src/Functional/Rest/MessageXmlCookieTest.php
+++ b/core/modules/contact/tests/src/Functional/Rest/MessageXmlCookieTest.php
@@ -23,6 +23,11 @@ class MessageXmlCookieTest extends MessageResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contact/tests/src/Functional/Views/ContactLinkTest.php b/core/modules/contact/tests/src/Functional/Views/ContactLinkTest.php
index 9eed21e068cf0d4d16c1b13253c5a127ab7fe2f8..f277e08bae7556890a586bbbb3f55b5799cce133 100644
--- a/core/modules/contact/tests/src/Functional/Views/ContactLinkTest.php
+++ b/core/modules/contact/tests/src/Functional/Views/ContactLinkTest.php
@@ -29,6 +29,11 @@ class ContactLinkTest extends ViewTestBase {
    */
   public static $modules = ['contact_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/content_moderation/tests/src/Functional/ContentModerationAdminPathEntityConverterLanguageTest.php b/core/modules/content_moderation/tests/src/Functional/ContentModerationAdminPathEntityConverterLanguageTest.php
index 5018361b58d23aa19fe4c0062e08c362d0322f26..01cb98a1ffa7a8041e5bd780c0e105795b4e7a4f 100644
--- a/core/modules/content_moderation/tests/src/Functional/ContentModerationAdminPathEntityConverterLanguageTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ContentModerationAdminPathEntityConverterLanguageTest.php
@@ -16,4 +16,9 @@ class ContentModerationAdminPathEntityConverterLanguageTest extends AdminPathEnt
    */
   public static $modules = ['language', 'language_test', 'content_moderation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php b/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php
index cbe5807a5fbed274d7892e26630f5fdfecb86cff..144765934e789faf80de80c40f35962039c03c5e 100644
--- a/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php
@@ -22,6 +22,11 @@ class ContentModerationWorkflowTypeTest extends BrowserTestBase {
     'entity_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/DefaultModerationStateTest.php b/core/modules/content_moderation/tests/src/Functional/DefaultModerationStateTest.php
index f5f6a5c004aae24ffc10f01b2c6c3bb552d47260..9e1f9035c8943ce0c85de092d1e09a52966ad4d4 100644
--- a/core/modules/content_moderation/tests/src/Functional/DefaultModerationStateTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/DefaultModerationStateTest.php
@@ -9,6 +9,11 @@
  */
 class DefaultModerationStateTest extends ModerationStateTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/LayoutBuilderContentModerationIntegrationTest.php b/core/modules/content_moderation/tests/src/Functional/LayoutBuilderContentModerationIntegrationTest.php
index 3f61ea9eeb6e2a4c10f9a81744cc46386291a4f1..c8a1493f9fdecdf214c499f646b503817af80be2 100644
--- a/core/modules/content_moderation/tests/src/Functional/LayoutBuilderContentModerationIntegrationTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/LayoutBuilderContentModerationIntegrationTest.php
@@ -26,6 +26,11 @@ class LayoutBuilderContentModerationIntegrationTest extends BrowserTestBase {
     'menu_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModeratedContentViewTest.php b/core/modules/content_moderation/tests/src/Functional/ModeratedContentViewTest.php
index b6ca37e94a55db6a3a1e7e4bcdcf5af31a2115e0..0faf532f3c2868ade622134510eb9339d4bdfb2d 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModeratedContentViewTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModeratedContentViewTest.php
@@ -34,6 +34,11 @@ class ModeratedContentViewTest extends BrowserTestBase {
     'content_translation',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationActionsTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationActionsTest.php
index 2df82eb5d56b9ca856bd1fb37e3b1b7d70d1baea..267e9a8df54d7de7394f637375fca0066fecfae0 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationActionsTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationActionsTest.php
@@ -28,6 +28,11 @@ class ModerationActionsTest extends BrowserTestBase {
     'views',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationContentTranslationTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationContentTranslationTest.php
index 4afa97de6f4c8f1744f77acb8463d514e1daf1db..a36d23af00eb61329da6fa809f79c095539c5087 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationContentTranslationTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationContentTranslationTest.php
@@ -32,6 +32,11 @@ class ModerationContentTranslationTest extends BrowserTestBase {
     'content_translation',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationFormTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationFormTest.php
index 679885c05900de254c7717629e05431ea7fcfe8a..4774f284b001f3d2c9e8df3cc81d4392ae38f7ea 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationFormTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationFormTest.php
@@ -24,6 +24,11 @@ class ModerationFormTest extends ModerationStateTestBase {
     'content_translation',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationLocaleTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationLocaleTest.php
index 1bdbb7e461104ace7cfed5877cc9c6eb54aa4500..e61ab2da69c6804ff4db1b4ede73f260eb1a6a36 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationLocaleTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationLocaleTest.php
@@ -23,6 +23,11 @@ class ModerationLocaleTest extends ModerationStateTestBase {
     'content_translation',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationRevisionRevertTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationRevisionRevertTest.php
index 6e54d682ff6ac759a0858294c572b90072b42e0c..d7e9f13fc08ebe13bc45d128fdded769289b6f8f 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationRevisionRevertTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationRevisionRevertTest.php
@@ -26,6 +26,11 @@ class ModerationRevisionRevertTest extends BrowserTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationStateAccessTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationStateAccessTest.php
index 09d5c8db64f23337f8cc1ec074865471b7a6d25f..51b24daf4e801b96ece4082287d447c9568958cb 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationStateAccessTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationStateAccessTest.php
@@ -24,6 +24,11 @@ class ModerationStateAccessTest extends BrowserTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationStateBlockTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationStateBlockTest.php
index 8b02848a30c2bbf568e94ba0019f56ead5a091d5..06bd9a9c31e45e9394b0d40d137855aca3bd2b08 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationStateBlockTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationStateBlockTest.php
@@ -12,6 +12,11 @@
  */
 class ModerationStateBlockTest extends ModerationStateTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTest.php
index 8fd580896bf014fef1daa3a1db9a77aa4e975664..d04c42c84330e117b9b3b1909528d59289a3b4b6 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTest.php
@@ -12,6 +12,11 @@
  */
 class ModerationStateNodeTest extends ModerationStateTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTypeTest.php b/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTypeTest.php
index a0a5fe01f8d53e67653b200c43b06de631f733be..476642f0ad9108266a80031a13ff48f98953c360 100644
--- a/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTypeTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ModerationStateNodeTypeTest.php
@@ -9,6 +9,11 @@
  */
 class ModerationStateNodeTypeTest extends ModerationStateTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A node type without moderation state disabled.
    *
diff --git a/core/modules/content_moderation/tests/src/Functional/NodeAccessTest.php b/core/modules/content_moderation/tests/src/Functional/NodeAccessTest.php
index 76e9d97608c48c44f52c945bc8aff40448f6ab03..5bee9bcb17136337b9eb56b33ea6b4f9ae3d6f90 100644
--- a/core/modules/content_moderation/tests/src/Functional/NodeAccessTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/NodeAccessTest.php
@@ -24,6 +24,11 @@ class NodeAccessTest extends ModerationStateTestBase {
     'node_access_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Permissions to grant admin user.
    *
diff --git a/core/modules/content_moderation/tests/src/Functional/ViewsModerationStateFilterTest.php b/core/modules/content_moderation/tests/src/Functional/ViewsModerationStateFilterTest.php
index e7b1d35b05a0a65e7819d0cc6aaa94aace91a11a..9598e1bd081ecba4b4e85d5bffa097828402a8b3 100644
--- a/core/modules/content_moderation/tests/src/Functional/ViewsModerationStateFilterTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ViewsModerationStateFilterTest.php
@@ -34,6 +34,11 @@ class ViewsModerationStateFilterTest extends ViewTestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_moderation/tests/src/Functional/WorkspaceContentModerationIntegrationTest.php b/core/modules/content_moderation/tests/src/Functional/WorkspaceContentModerationIntegrationTest.php
index 2227c2dac50ccb738b83f434902b2728cf093cbb..e2430e22adcdf8973ffd4e39b92298a714517d58 100644
--- a/core/modules/content_moderation/tests/src/Functional/WorkspaceContentModerationIntegrationTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/WorkspaceContentModerationIntegrationTest.php
@@ -20,6 +20,11 @@ class WorkspaceContentModerationIntegrationTest extends ModerationStateTestBase
    */
   public static $modules = ['node', 'workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTestTranslationUITest.php b/core/modules/content_translation/tests/src/Functional/ContentTestTranslationUITest.php
index 0b1de0b204f4ff108b12d0b80e11130c58f21a31..1480c41dc6dc794376e14fbc751aad313d97cd65 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTestTranslationUITest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTestTranslationUITest.php
@@ -21,6 +21,11 @@ class ContentTestTranslationUITest extends ContentTranslationUITestBase {
    */
   public static $modules = ['language', 'content_translation', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationContextualLinksTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationContextualLinksTest.php
index 8042d9100707447995a4fdacefd02273d2758313..e2a945b011d0f93090484ed022971c3ee41e1806 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationContextualLinksTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationContextualLinksTest.php
@@ -21,6 +21,11 @@ class ContentTranslationContextualLinksTest extends BrowserTestBase {
    */
   protected $bundle;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The content type being tested.
    *
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationDisableSettingTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationDisableSettingTest.php
index 6dffed7444b691a60b078314e81b4637fc8b05bc..5b56f880c7d73cbdb7c85a5ea17725c2fe364493 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationDisableSettingTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationDisableSettingTest.php
@@ -20,6 +20,11 @@ class ContentTranslationDisableSettingTest extends BrowserTestBase {
     'language',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that entity schemas are up-to-date after enabling translation.
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationEnableTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationEnableTest.php
index a3cc4e99466c59333193e355f87f32ff8ad37fd8..7ae73a8fd73dfa54bd21de8d1a3e7a40a32f7748 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationEnableTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationEnableTest.php
@@ -16,6 +16,11 @@ class ContentTranslationEnableTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'menu_link_content', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that entity schemas are up-to-date after enabling translation.
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationEntityBundleUITest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationEntityBundleUITest.php
index 163b5e8ff31e15e120abce81c95c9946bbc42b1f..dfd291bd858c723342e77588eb94cd4c3a68c97e 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationEntityBundleUITest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationEntityBundleUITest.php
@@ -13,6 +13,11 @@ class ContentTranslationEntityBundleUITest extends BrowserTestBase {
 
   public static $modules = ['language', 'content_translation', 'node', 'comment', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $user = $this->drupalCreateUser(['access administration pages', 'administer languages', 'administer content translation', 'administer content types']);
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationLanguageChangeTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationLanguageChangeTest.php
index 1bf836aaca8769fac179c05ee79da586901f0bc3..b72af04df81ef3a0198625ae6e7b64607e7d6d34 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationLanguageChangeTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationLanguageChangeTest.php
@@ -24,6 +24,11 @@ class ContentTranslationLanguageChangeTest extends NodeTestBase {
    */
   public static $modules = ['language', 'content_translation', 'content_translation_test', 'node', 'block', 'field_ui', 'image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationLinkTagTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationLinkTagTest.php
index 8ea652e954d30309be25d888c1a3f2569f716377..2e77e70cb6e108d521c61cec7f6525828ecc00dd 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationLinkTagTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationLinkTagTest.php
@@ -19,6 +19,11 @@ class ContentTranslationLinkTagTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'content_translation', 'content_translation_test', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The added languages.
    *
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationOperationsTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationOperationsTest.php
index 8486ac529ff016e18429de0d1a4a53fa97701824..d2e4ba0224519fb2720f7717c3b47c4e7f0dda98 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationOperationsTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationOperationsTest.php
@@ -20,6 +20,11 @@ class ContentTranslationOperationsTest extends NodeTestBase {
    */
   protected $baseUser1;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A base user.
    *
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationOutdatedRevisionTranslationTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationOutdatedRevisionTranslationTest.php
index d37f5d8ec4a982adf4d5a9e03e58a04c011cf365..f91d3fd9b1d19a8d22b0551c231348ae49ce2674 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationOutdatedRevisionTranslationTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationOutdatedRevisionTranslationTest.php
@@ -12,6 +12,11 @@
  */
 class ContentTranslationOutdatedRevisionTranslationTest extends ContentTranslationPendingRevisionTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationRevisionTranslationDeletionTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationRevisionTranslationDeletionTest.php
index 842d7deda8c4b806d2d71e815d063e53caf9154e..dd9c04e6ca4dd0af3b16f2a7afd2c66d0e2fc59b 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationRevisionTranslationDeletionTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationRevisionTranslationDeletionTest.php
@@ -12,6 +12,11 @@
  */
 class ContentTranslationRevisionTranslationDeletionTest extends ContentTranslationPendingRevisionTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationSettingsTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationSettingsTest.php
index 8b6565a6c517c538bfdcf1b0ede8a8503526106b..4708fe8146cc668298cb3d3cbab5438e97af6746 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationSettingsTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationSettingsTest.php
@@ -27,6 +27,11 @@ class ContentTranslationSettingsTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'content_translation', 'node', 'comment', 'field_ui', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationSyncImageTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationSyncImageTest.php
index cc5f5c0e70c5a238394bcef1c6d55ea3a2f6d0f1..899d1ada68f36e027c7a08fb2f509f929847719f 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationSyncImageTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationSyncImageTest.php
@@ -20,6 +20,11 @@ class ContentTranslationSyncImageTest extends ContentTranslationTestBase {
     getTestFiles as drupalGetTestFiles;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The cardinality of the image field.
    *
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationUISkipTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationUISkipTest.php
index 97d0b00f5da6a01a6b5dccb5ed7d21282432a5fd..7f3582d207c25f1fb111312a3da05cdc17982649 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationUISkipTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationUISkipTest.php
@@ -18,6 +18,11 @@ class ContentTranslationUISkipTest extends BrowserTestBase {
    */
   public static $modules = ['content_translation_test', 'user', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the content_translation_ui_skip key functionality.
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationUntranslatableFieldsTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationUntranslatableFieldsTest.php
index 3d7acfd6d803e49468e04307488b0d2d83468f90..6623a3504439bb1e8408e84a0b3599979e2d2ade 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationUntranslatableFieldsTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationUntranslatableFieldsTest.php
@@ -19,6 +19,11 @@ class ContentTranslationUntranslatableFieldsTest extends ContentTranslationPendi
    */
   public static $modules = ['field_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/content_translation/tests/src/Functional/ContentTranslationWorkflowsTest.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationWorkflowsTest.php
index 2407d4f4411395ca977bc1808ccb89d0a6e14b9d..2efc272143cf1fcbd732c06f3e0b8492deffb9f9 100644
--- a/core/modules/content_translation/tests/src/Functional/ContentTranslationWorkflowsTest.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationWorkflowsTest.php
@@ -31,6 +31,11 @@ class ContentTranslationWorkflowsTest extends ContentTranslationTestBase {
    */
   public static $modules = ['language', 'content_translation', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->setupEntity();
diff --git a/core/modules/content_translation/tests/src/Functional/Views/ContentTranslationViewsUITest.php b/core/modules/content_translation/tests/src/Functional/Views/ContentTranslationViewsUITest.php
index 4b4d53a484d8780c225fc5c0ca64a7b5f0049d46..351ff78de72416cf832b7432122c431d8d600902 100644
--- a/core/modules/content_translation/tests/src/Functional/Views/ContentTranslationViewsUITest.php
+++ b/core/modules/content_translation/tests/src/Functional/Views/ContentTranslationViewsUITest.php
@@ -25,6 +25,11 @@ class ContentTranslationViewsUITest extends UITestBase {
    */
   public static $modules = ['content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the views UI.
    */
diff --git a/core/modules/content_translation/tests/src/Functional/Views/TranslationLinkTest.php b/core/modules/content_translation/tests/src/Functional/Views/TranslationLinkTest.php
index d2e9e0d0cbeda0f4a8df093a6aedd1d08d1014c6..6370ca8391ff638e3ef175edd5163225cb69f177 100644
--- a/core/modules/content_translation/tests/src/Functional/Views/TranslationLinkTest.php
+++ b/core/modules/content_translation/tests/src/Functional/Views/TranslationLinkTest.php
@@ -29,6 +29,11 @@ class TranslationLinkTest extends ContentTranslationTestBase {
    */
   public static $modules = ['content_translation_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     // @todo Use entity_type once it is has multilingual Views integration.
     $this->entityTypeId = 'user';
diff --git a/core/modules/content_translation/tests/src/FunctionalJavascript/ContentTranslationContextualLinksTest.php b/core/modules/content_translation/tests/src/FunctionalJavascript/ContentTranslationContextualLinksTest.php
index 156b10d97ff91c5a37b8f66703aa576ffcae8bcf..4f8a1b55775207087d249787610a59cf3ec4b298 100644
--- a/core/modules/content_translation/tests/src/FunctionalJavascript/ContentTranslationContextualLinksTest.php
+++ b/core/modules/content_translation/tests/src/FunctionalJavascript/ContentTranslationContextualLinksTest.php
@@ -24,6 +24,11 @@ class ContentTranslationContextualLinksTest extends WebDriverTestBase {
    */
   public static $modules = ['content_translation', 'contextual', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contextual/tests/src/Functional/ContextualDynamicContextTest.php b/core/modules/contextual/tests/src/Functional/ContextualDynamicContextTest.php
index 74a6d504e80ad81515d4402365b22f61871e39f3..4f0ab275ff528709597e99e4fee1c27e3e49d254 100644
--- a/core/modules/contextual/tests/src/Functional/ContextualDynamicContextTest.php
+++ b/core/modules/contextual/tests/src/Functional/ContextualDynamicContextTest.php
@@ -17,6 +17,11 @@
  */
 class ContextualDynamicContextTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with permission to access contextual links and edit content.
    *
diff --git a/core/modules/contextual/tests/src/FunctionalJavascript/ContextualLinksTest.php b/core/modules/contextual/tests/src/FunctionalJavascript/ContextualLinksTest.php
index 29d2ec7be5b88975e28f3c046b11adc078b9fa50..74d733e162c195513af40cf6f9950032c61fd411 100644
--- a/core/modules/contextual/tests/src/FunctionalJavascript/ContextualLinksTest.php
+++ b/core/modules/contextual/tests/src/FunctionalJavascript/ContextualLinksTest.php
@@ -19,6 +19,11 @@ class ContextualLinksTest extends WebDriverTestBase {
    */
   public static $modules = ['block', 'contextual'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
index 4a00a7efc491c931eb4a4702d42384dc76666a71..0133bca215ed72c49bd7e7ec09dcf369607ffe8a 100644
--- a/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
+++ b/core/modules/contextual/tests/src/FunctionalJavascript/EditModeTest.php
@@ -29,6 +29,11 @@ class EditModeTest extends WebDriverTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/datetime/tests/src/Functional/DateFilterTest.php b/core/modules/datetime/tests/src/Functional/DateFilterTest.php
index 37018d8341deabee7882e0f9b94641fddfda9da8..0272bb25e1a664530b866612fa1091b661c7baa7 100644
--- a/core/modules/datetime/tests/src/Functional/DateFilterTest.php
+++ b/core/modules/datetime/tests/src/Functional/DateFilterTest.php
@@ -42,6 +42,11 @@ class DateFilterTest extends ViewTestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/datetime/tests/src/Functional/DateTimeFieldTest.php b/core/modules/datetime/tests/src/Functional/DateTimeFieldTest.php
index 1ffa0e865b80a24d4177911778bfb2f816fb429c..fd55a918f31837ec4a16cd08f47d932083db7ed5 100644
--- a/core/modules/datetime/tests/src/Functional/DateTimeFieldTest.php
+++ b/core/modules/datetime/tests/src/Functional/DateTimeFieldTest.php
@@ -25,6 +25,11 @@ class DateTimeFieldTest extends DateTestBase {
    */
   protected $defaultSettings = ['timezone_override' => ''];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/datetime/tests/src/Functional/DateTimeTimeAgoFormatterTest.php b/core/modules/datetime/tests/src/Functional/DateTimeTimeAgoFormatterTest.php
index d143413cbbf4069985b3eb2063b21f3e8ed177fb..2d777d646496ab9200e9c68400754a92499fc20b 100644
--- a/core/modules/datetime/tests/src/Functional/DateTimeTimeAgoFormatterTest.php
+++ b/core/modules/datetime/tests/src/Functional/DateTimeTimeAgoFormatterTest.php
@@ -41,6 +41,11 @@ class DateTimeTimeAgoFormatterTest extends BrowserTestBase {
    */
   public static $modules = ['datetime', 'entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
index e8c71ef0ccf3f217407cefc7d804e5c7a227bb60..9d00406d5fd96539ab713fa01f7e3390cadb69c8 100644
--- a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
@@ -27,6 +27,11 @@ class EntityTestDateonlyTest extends EntityTestResourceTestBase {
    */
   protected static $dateString = '2017-03-01';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Datetime test field name.
    *
diff --git a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
index f5efce53f383a21d355df829766920ba14c3a4e4..a2134650b4e13f5794391b6b5bef9347fe6ccea7 100644
--- a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
@@ -27,6 +27,11 @@ class EntityTestDatetimeTest extends EntityTestResourceTestBase {
    */
   protected static $dateString = '2017-03-01T20:02:00';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Datetime test field name.
    *
diff --git a/core/modules/datetime/tests/src/Functional/Views/FilterDateTest.php b/core/modules/datetime/tests/src/Functional/Views/FilterDateTest.php
index 6c106497ae2d2544d23d0e0f625fca0a95ceab97..213d422fe55f26d5abb372792dd2919b7a8534be 100644
--- a/core/modules/datetime/tests/src/Functional/Views/FilterDateTest.php
+++ b/core/modules/datetime/tests/src/Functional/Views/FilterDateTest.php
@@ -26,6 +26,11 @@ class FilterDateTest extends BrowserTestBase {
    */
   protected $fieldName = 'field_date';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Nodes to test.
    *
diff --git a/core/modules/datetime_range/tests/src/Functional/DateRangeFieldTest.php b/core/modules/datetime_range/tests/src/Functional/DateRangeFieldTest.php
index 65faabf97fb6f977557ad7a53a669f99868194a8..cdf95cce14b84cd926420fe654f64904a67fd8c5 100644
--- a/core/modules/datetime_range/tests/src/Functional/DateRangeFieldTest.php
+++ b/core/modules/datetime_range/tests/src/Functional/DateRangeFieldTest.php
@@ -27,6 +27,11 @@ class DateRangeFieldTest extends DateTestBase {
    */
   public static $modules = ['datetime_range'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The default display settings to use for the formatters.
    *
diff --git a/core/modules/datetime_range/tests/src/Functional/EntityResource/EntityTest/EntityTestDateRangeTest.php b/core/modules/datetime_range/tests/src/Functional/EntityResource/EntityTest/EntityTestDateRangeTest.php
index e669a22371097b9f1e19a0a8ef60b485f6bc7955..07c819d48f0b160d491364b0780d7dafd456eecb 100644
--- a/core/modules/datetime_range/tests/src/Functional/EntityResource/EntityTest/EntityTestDateRangeTest.php
+++ b/core/modules/datetime_range/tests/src/Functional/EntityResource/EntityTest/EntityTestDateRangeTest.php
@@ -39,6 +39,11 @@ class EntityTestDateRangeTest extends EntityTestResourceTestBase {
    */
   public static $modules = ['datetime_range', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/dblog/tests/src/Functional/DbLogResourceTest.php b/core/modules/dblog/tests/src/Functional/DbLogResourceTest.php
index fc22d49182eaafb6ed4512bdde2448e1a72f54a1..5a45f63cc05c4b9694583aa122ea7f8fea4e8262 100644
--- a/core/modules/dblog/tests/src/Functional/DbLogResourceTest.php
+++ b/core/modules/dblog/tests/src/Functional/DbLogResourceTest.php
@@ -17,6 +17,11 @@ class DbLogResourceTest extends ResourceTestBase {
 
   use CookieResourceTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/dblog/tests/src/Functional/DbLogTest.php b/core/modules/dblog/tests/src/Functional/DbLogTest.php
index 87856ce4a8746b5fffe70110dcedfbce470f4ef1..ee08a29001208f07ac1a29bd54cf283b1d40529e 100644
--- a/core/modules/dblog/tests/src/Functional/DbLogTest.php
+++ b/core/modules/dblog/tests/src/Functional/DbLogTest.php
@@ -28,6 +28,11 @@ class DbLogTest extends BrowserTestBase {
    */
   public static $modules = ['dblog', 'node', 'forum', 'help', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with some relevant administrative permissions.
    *
diff --git a/core/modules/dblog/tests/src/Functional/DbLogViewsTest.php b/core/modules/dblog/tests/src/Functional/DbLogViewsTest.php
index 6e525cdf6f9dfe748dc91c5c02694637384eef6d..cbb86f8c54e0859653061b669addb3d69130f76f 100644
--- a/core/modules/dblog/tests/src/Functional/DbLogViewsTest.php
+++ b/core/modules/dblog/tests/src/Functional/DbLogViewsTest.php
@@ -21,6 +21,11 @@ class DbLogViewsTest extends DbLogTest {
    */
   public static $modules = ['dblog', 'node', 'forum', 'help', 'block', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/dynamic_page_cache/tests/src/Functional/DynamicPageCacheIntegrationTest.php b/core/modules/dynamic_page_cache/tests/src/Functional/DynamicPageCacheIntegrationTest.php
index ffa8f4375f64f53a5937f740e9761ef784d3595b..1574679c24c809f7441b1f0f6774ead5113d3bde 100644
--- a/core/modules/dynamic_page_cache/tests/src/Functional/DynamicPageCacheIntegrationTest.php
+++ b/core/modules/dynamic_page_cache/tests/src/Functional/DynamicPageCacheIntegrationTest.php
@@ -32,6 +32,11 @@ class DynamicPageCacheIntegrationTest extends BrowserTestBase {
    */
   protected static $modules = ['dynamic_page_cache_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/editor/tests/src/Functional/EditorAdminTest.php b/core/modules/editor/tests/src/Functional/EditorAdminTest.php
index 7995b6629b40efc71ecba4e83d898ebd236c4b38..780fa3b145efd8a78a56f552611c4253b2eb3e1e 100644
--- a/core/modules/editor/tests/src/Functional/EditorAdminTest.php
+++ b/core/modules/editor/tests/src/Functional/EditorAdminTest.php
@@ -22,6 +22,11 @@ class EditorAdminTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'editor'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with the 'administer filters' permission.
    *
diff --git a/core/modules/editor/tests/src/Functional/EditorDialogAccessTest.php b/core/modules/editor/tests/src/Functional/EditorDialogAccessTest.php
index 3a97b351b34d83043755d5a9dd1619f507465135..46a41a6a7226bbe5ca614436c1b9f61e39f5ecd2 100644
--- a/core/modules/editor/tests/src/Functional/EditorDialogAccessTest.php
+++ b/core/modules/editor/tests/src/Functional/EditorDialogAccessTest.php
@@ -20,6 +20,11 @@ class EditorDialogAccessTest extends BrowserTestBase {
    */
   public static $modules = ['editor', 'filter', 'ckeditor'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test access to the editor image dialog.
    */
diff --git a/core/modules/editor/tests/src/Functional/EditorLoadingTest.php b/core/modules/editor/tests/src/Functional/EditorLoadingTest.php
index 36ab8e896cc21a36049b1f19176b1d53c021e85e..d02c744b3d4ec1e653e8e3c80983fd68bbd4f554 100644
--- a/core/modules/editor/tests/src/Functional/EditorLoadingTest.php
+++ b/core/modules/editor/tests/src/Functional/EditorLoadingTest.php
@@ -22,6 +22,11 @@ class EditorLoadingTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'editor', 'editor_test', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An untrusted user, with access to the 'plain_text' format.
    *
diff --git a/core/modules/editor/tests/src/Functional/EditorPrivateFileReferenceFilterTest.php b/core/modules/editor/tests/src/Functional/EditorPrivateFileReferenceFilterTest.php
index 4880c85fc8e13c6a222777c2430a34ae556e87f7..c99a53cb48dfffd0313b4700dd4d3333668d0d38 100644
--- a/core/modules/editor/tests/src/Functional/EditorPrivateFileReferenceFilterTest.php
+++ b/core/modules/editor/tests/src/Functional/EditorPrivateFileReferenceFilterTest.php
@@ -33,6 +33,11 @@ class EditorPrivateFileReferenceFilterTest extends BrowserTestBase {
     'editor_private_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the editor file reference filter with private files.
    */
diff --git a/core/modules/editor/tests/src/Functional/EditorSecurityTest.php b/core/modules/editor/tests/src/Functional/EditorSecurityTest.php
index 2428f70d6ea7d3f929596a8c55bf252b5688ee26..c6bd6495b5f9757aa1e30747e21a9abf798c851d 100644
--- a/core/modules/editor/tests/src/Functional/EditorSecurityTest.php
+++ b/core/modules/editor/tests/src/Functional/EditorSecurityTest.php
@@ -22,6 +22,11 @@ class EditorSecurityTest extends BrowserTestBase {
    */
   protected static $sampleContent = '<p style="color: red">Hello, Dumbo Octopus!</p><script>alert(0)</script><embed type="image/svg+xml" src="image.svg" />';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The secured sample content to use in most tests.
    *
diff --git a/core/modules/editor/tests/src/Functional/EditorUploadImageScaleTest.php b/core/modules/editor/tests/src/Functional/EditorUploadImageScaleTest.php
index 46f9a6e4589d6315275f4d374d3b6a6bd1201143..b7a88d809c5f21a1eb93018188a4d0c6a05bf5f3 100644
--- a/core/modules/editor/tests/src/Functional/EditorUploadImageScaleTest.php
+++ b/core/modules/editor/tests/src/Functional/EditorUploadImageScaleTest.php
@@ -24,6 +24,11 @@ class EditorUploadImageScaleTest extends BrowserTestBase {
    */
   public static $modules = ['editor', 'editor_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission as administer for testing.
    *
diff --git a/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonAnonTest.php b/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonAnonTest.php
index 97d917d6dcaadd54b22daa07c341a17e7665c21d..473e3c9255df4e943cb2e9d0e7172a203046479e 100644
--- a/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonAnonTest.php
+++ b/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class EditorHalJsonAnonTest extends EditorResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonBasicAuthTest.php b/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonBasicAuthTest.php
index 05f496bb6fa1c381caf415ce17ca17e6948d7470..57042e58b4508ed3d9bac9fbef02d05b78230c65 100644
--- a/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonBasicAuthTest.php
+++ b/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class EditorHalJsonBasicAuthTest extends EditorResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonCookieTest.php b/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonCookieTest.php
index 4fe7ec988598ba915125246bf4ba682d7c16200f..b2db5fb34ac7fa5b439ef1a5286fa71b95051dd2 100644
--- a/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonCookieTest.php
+++ b/core/modules/editor/tests/src/Functional/Hal/EditorHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class EditorHalJsonCookieTest extends EditorResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/editor/tests/src/Functional/QuickEditIntegrationLoadingTest.php b/core/modules/editor/tests/src/Functional/QuickEditIntegrationLoadingTest.php
index 396c30a8a6a56473f27a392a72976b810043590e..56916776f63c13f709a1ee4b93cd3ed1622780ab 100644
--- a/core/modules/editor/tests/src/Functional/QuickEditIntegrationLoadingTest.php
+++ b/core/modules/editor/tests/src/Functional/QuickEditIntegrationLoadingTest.php
@@ -21,6 +21,11 @@ class QuickEditIntegrationLoadingTest extends BrowserTestBase {
    */
   public static $modules = ['quickedit', 'filter', 'node', 'editor'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The basic permissions necessary to view content and use in-place editing.
    *
diff --git a/core/modules/editor/tests/src/Functional/Rest/EditorJsonAnonTest.php b/core/modules/editor/tests/src/Functional/Rest/EditorJsonAnonTest.php
index 3809f0aedd5149f805498a7ede8f3e7e7910812a..53bc36b8863f22507fb80d57fea8100997b02924 100644
--- a/core/modules/editor/tests/src/Functional/Rest/EditorJsonAnonTest.php
+++ b/core/modules/editor/tests/src/Functional/Rest/EditorJsonAnonTest.php
@@ -21,4 +21,9 @@ class EditorJsonAnonTest extends EditorResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/editor/tests/src/Functional/Rest/EditorJsonBasicAuthTest.php b/core/modules/editor/tests/src/Functional/Rest/EditorJsonBasicAuthTest.php
index f0c301030a4fa57cc6177c19a78e66417164bfea..3b39696a963740d9c632ac8fbdde63f8031823b6 100644
--- a/core/modules/editor/tests/src/Functional/Rest/EditorJsonBasicAuthTest.php
+++ b/core/modules/editor/tests/src/Functional/Rest/EditorJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EditorJsonBasicAuthTest extends EditorResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/editor/tests/src/Functional/Rest/EditorJsonCookieTest.php b/core/modules/editor/tests/src/Functional/Rest/EditorJsonCookieTest.php
index 95f1024c67b970d017c05a27ca3bec98e52ce77c..b840c7a1029d6c588839c224e1d449bc1f2ab596 100644
--- a/core/modules/editor/tests/src/Functional/Rest/EditorJsonCookieTest.php
+++ b/core/modules/editor/tests/src/Functional/Rest/EditorJsonCookieTest.php
@@ -26,4 +26,9 @@ class EditorJsonCookieTest extends EditorResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/editor/tests/src/Functional/Rest/EditorXmlAnonTest.php b/core/modules/editor/tests/src/Functional/Rest/EditorXmlAnonTest.php
index d5be1f6deb7b0041dfbb6fa0ff4ed0e8fbac4138..79129309c621335077fcde418a0580fea14292d6 100644
--- a/core/modules/editor/tests/src/Functional/Rest/EditorXmlAnonTest.php
+++ b/core/modules/editor/tests/src/Functional/Rest/EditorXmlAnonTest.php
@@ -23,4 +23,9 @@ class EditorXmlAnonTest extends EditorResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/editor/tests/src/Functional/Rest/EditorXmlBasicAuthTest.php b/core/modules/editor/tests/src/Functional/Rest/EditorXmlBasicAuthTest.php
index acab40b9a4706c48cf177c02ed175653e3483547..5e5aa467f5061416d41093f59b61aa8734a825b7 100644
--- a/core/modules/editor/tests/src/Functional/Rest/EditorXmlBasicAuthTest.php
+++ b/core/modules/editor/tests/src/Functional/Rest/EditorXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class EditorXmlBasicAuthTest extends EditorResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/editor/tests/src/Functional/Rest/EditorXmlCookieTest.php b/core/modules/editor/tests/src/Functional/Rest/EditorXmlCookieTest.php
index 8940095162de95becf93d2cd838db6909c181a0d..fdafcaa9a4cf466b49d9dbd57efff58292eb5564 100644
--- a/core/modules/editor/tests/src/Functional/Rest/EditorXmlCookieTest.php
+++ b/core/modules/editor/tests/src/Functional/Rest/EditorXmlCookieTest.php
@@ -28,4 +28,9 @@ class EditorXmlCookieTest extends EditorResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/editor/tests/src/FunctionalJavascript/EditorAdminTest.php b/core/modules/editor/tests/src/FunctionalJavascript/EditorAdminTest.php
index 6652bdaec5b4299129b6510f70881ae55a8c4ad2..d3cea975525156cd1f7f74df99f995dc14921964 100644
--- a/core/modules/editor/tests/src/FunctionalJavascript/EditorAdminTest.php
+++ b/core/modules/editor/tests/src/FunctionalJavascript/EditorAdminTest.php
@@ -23,6 +23,11 @@ class EditorAdminTest extends WebDriverTestBase {
     'ckeditor',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php b/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php
index 5d85c654650e0995f81d92af25ab2c5dc9c3fd12..4852229a15790956db884b6d7d31899fb3808c29 100644
--- a/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php
+++ b/core/modules/field/tests/src/Functional/Boolean/BooleanFieldTest.php
@@ -26,6 +26,11 @@ class BooleanFieldTest extends BrowserTestBase {
     'field_test_boolean_access_denied',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A field to use in this test class.
    *
diff --git a/core/modules/field/tests/src/Functional/Boolean/BooleanFormatterSettingsTest.php b/core/modules/field/tests/src/Functional/Boolean/BooleanFormatterSettingsTest.php
index af92c3f7354dc4b45a228f375b6c3fb22e0a4f2d..532c3992961b1e297a93ac84e6ac338f627d8af0 100644
--- a/core/modules/field/tests/src/Functional/Boolean/BooleanFormatterSettingsTest.php
+++ b/core/modules/field/tests/src/Functional/Boolean/BooleanFormatterSettingsTest.php
@@ -20,6 +20,11 @@ class BooleanFormatterSettingsTest extends BrowserTestBase {
    */
   public static $modules = ['field', 'field_ui', 'text', 'node', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the entity bundle that is created in the test.
    *
diff --git a/core/modules/field/tests/src/Functional/Email/EmailFieldTest.php b/core/modules/field/tests/src/Functional/Email/EmailFieldTest.php
index 3fb80a85d4639472477cf7965ff94209a49edce0..c044ba3c1c5a75991d6906fa1bc945eed2328ba2 100644
--- a/core/modules/field/tests/src/Functional/Email/EmailFieldTest.php
+++ b/core/modules/field/tests/src/Functional/Email/EmailFieldTest.php
@@ -21,6 +21,11 @@ class EmailFieldTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A field storage to use in this test class.
    *
diff --git a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAdminTest.php b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAdminTest.php
index 9d82101c0ad421c1dc9c1ab903fcc47fc85cfe02..bdb755c1d18e7bd5d7242227e970cd68d2581f0a 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAdminTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAdminTest.php
@@ -30,6 +30,11 @@ class EntityReferenceAdminTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'field_ui', 'path', 'taxonomy', 'block', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the content type created for testing purposes.
    *
diff --git a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAutoCreateTest.php b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAutoCreateTest.php
index 9c7b9b46c3091448c5e0a05100625e77bcd28194..0e5deb0324cd05d376c774852a6ad0c764785be0 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAutoCreateTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceAutoCreateTest.php
@@ -21,6 +21,11 @@ class EntityReferenceAutoCreateTest extends BrowserTestBase {
 
   public static $modules = ['node', 'taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of a content type that will reference $referencedType.
    *
diff --git a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldDefaultValueTest.php b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldDefaultValueTest.php
index 89d30eb27cb2695d88d9114f134dd588ed84edde..9f50ed63ba1d26b4b42c22ba1e9d53bbb9d2831b 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldDefaultValueTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldDefaultValueTest.php
@@ -24,6 +24,11 @@ class EntityReferenceFieldDefaultValueTest extends BrowserTestBase {
    */
   public static $modules = ['field_ui', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to administer content types, node fields, etc.
    *
diff --git a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldTranslatedReferenceViewTest.php b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldTranslatedReferenceViewTest.php
index f327d4cd42eabc366f79487b3de409b70dcde88b..79ba27170b6f120696b01109bb2c4d22c84dd931 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldTranslatedReferenceViewTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFieldTranslatedReferenceViewTest.php
@@ -124,6 +124,11 @@ class EntityReferenceFieldTranslatedReferenceViewTest extends BrowserTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFileUploadTest.php b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFileUploadTest.php
index 7892aa8671796dd65944ea34d53cf9c1847da3f7..11374c9dd7216e33c87e48800d864fd020e57303 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFileUploadTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceFileUploadTest.php
@@ -19,6 +19,11 @@ class EntityReferenceFileUploadTest extends BrowserTestBase {
 
   public static $modules = ['entity_reference', 'node', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of a content type that will reference $referencedType.
    *
diff --git a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceIntegrationTest.php b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceIntegrationTest.php
index 9c67d043f77e10844c74a683bc92126348cabf94..9cc161396ed1ce437746f16082d21381f538f2e9 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceIntegrationTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceIntegrationTest.php
@@ -47,6 +47,11 @@ class EntityReferenceIntegrationTest extends BrowserTestBase {
    */
   public static $modules = ['config_test', 'entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceXSSTest.php b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceXSSTest.php
index a1867c2589bcec1689360fa31eee4448e05fedd4..15529854dded16ed73f48c4b992b6d24dc227988 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceXSSTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/EntityReferenceXSSTest.php
@@ -23,6 +23,11 @@ class EntityReferenceXSSTest extends BrowserTestBase {
    */
   protected static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests markup is escaped in the entity reference select and label formatter.
    */
diff --git a/core/modules/field/tests/src/Functional/EntityReference/Views/SelectionTest.php b/core/modules/field/tests/src/Functional/EntityReference/Views/SelectionTest.php
index 16a18d96c11ab7256799b1c34cecda199cded564..da732f6ffb71a8ba54785387e92d647ea9510393 100644
--- a/core/modules/field/tests/src/Functional/EntityReference/Views/SelectionTest.php
+++ b/core/modules/field/tests/src/Functional/EntityReference/Views/SelectionTest.php
@@ -29,6 +29,11 @@ class SelectionTest extends BrowserTestBase {
     'entity_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An array of node titles, keyed by content type and node ID.
    *
diff --git a/core/modules/field/tests/src/Functional/FieldAccessTest.php b/core/modules/field/tests/src/Functional/FieldAccessTest.php
index 55a2812abe612abfa863cad599a70aefc163671f..6a91bd1ef00dff69b7bc9f61fa0138f5c490d827 100644
--- a/core/modules/field/tests/src/Functional/FieldAccessTest.php
+++ b/core/modules/field/tests/src/Functional/FieldAccessTest.php
@@ -19,6 +19,11 @@ class FieldAccessTest extends FieldTestBase {
    */
   public static $modules = ['node', 'field_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Node entity to use in this test.
    *
diff --git a/core/modules/field/tests/src/Functional/FieldDefaultValueCallbackTest.php b/core/modules/field/tests/src/Functional/FieldDefaultValueCallbackTest.php
index 4a70e7171c7b422b69be2f61b47e37b5fe3e09c5..da28d7710ed502f11e7d92dd1b54b4f7fe9bb597 100644
--- a/core/modules/field/tests/src/Functional/FieldDefaultValueCallbackTest.php
+++ b/core/modules/field/tests/src/Functional/FieldDefaultValueCallbackTest.php
@@ -20,6 +20,11 @@ class FieldDefaultValueCallbackTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'field_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The field name.
    *
diff --git a/core/modules/field/tests/src/Functional/FieldHelpTest.php b/core/modules/field/tests/src/Functional/FieldHelpTest.php
index 712edec99acf192cd505e23693b3b44465a1aaf1..d0c2bb777fdc07f1ed1f39f840b4de9407d09e70 100644
--- a/core/modules/field/tests/src/Functional/FieldHelpTest.php
+++ b/core/modules/field/tests/src/Functional/FieldHelpTest.php
@@ -18,6 +18,11 @@ class FieldHelpTest extends BrowserTestBase {
    */
   public static $modules = ['field', 'help'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   // Tests field help implementation without optional core modules enabled.
   protected $profile = 'minimal';
 
diff --git a/core/modules/field/tests/src/Functional/FieldImportDeleteUninstallUiTest.php b/core/modules/field/tests/src/Functional/FieldImportDeleteUninstallUiTest.php
index 25a798b8b9ba74f7e87c7e80927bfbecaa1878ab..6641d691f9a96db63a6480e0875e32840168c648 100644
--- a/core/modules/field/tests/src/Functional/FieldImportDeleteUninstallUiTest.php
+++ b/core/modules/field/tests/src/Functional/FieldImportDeleteUninstallUiTest.php
@@ -24,6 +24,11 @@ class FieldImportDeleteUninstallUiTest extends FieldTestBase {
    */
   public static $modules = ['entity_test', 'telephone', 'config', 'filter', 'datetime'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/field/tests/src/Functional/FormTest.php b/core/modules/field/tests/src/Functional/FormTest.php
index 671f01ac50a3d0f233efe3b87114e9660968d21a..b409456cf945c63d6e1e540d2785990f4590a8a0 100644
--- a/core/modules/field/tests/src/Functional/FormTest.php
+++ b/core/modules/field/tests/src/Functional/FormTest.php
@@ -27,6 +27,11 @@ class FormTest extends FieldTestBase {
    */
   public static $modules = ['node', 'field_test', 'options', 'entity_test', 'locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An array of values defining a field single.
    *
diff --git a/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonAnonTest.php b/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonAnonTest.php
index 2137336c18d5df96bcb8f5b1f584f30c3f07d9fb..b32f25e5bf2d67a8603ae5686a808c12f8a1cf1d 100644
--- a/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonAnonTest.php
+++ b/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class FieldConfigHalJsonAnonTest extends FieldConfigResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonBasicAuthTest.php b/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonBasicAuthTest.php
index 8a299a4c4932f71a7691f94b09bbeb7ef17c640e..ce8838c1f33bfdc27ce8c950154db9417dd771e4 100644
--- a/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonBasicAuthTest.php
+++ b/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class FieldConfigHalJsonBasicAuthTest extends FieldConfigResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonCookieTest.php b/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonCookieTest.php
index c9f5ce0dd97f5eb7913b84e3ba8e20f9b457bbb1..b482ab03186d317425912a172c8b5e943bdf079a 100644
--- a/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonCookieTest.php
+++ b/core/modules/field/tests/src/Functional/Hal/FieldConfigHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class FieldConfigHalJsonCookieTest extends FieldConfigResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonAnonTest.php b/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonAnonTest.php
index 7e74390b3859ea0e8806ed82858594f9b356f0d9..72bc55058e250e4c00c9d772e373db9dc756fe1a 100644
--- a/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonAnonTest.php
+++ b/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class FieldStorageConfigHalJsonAnonTest extends FieldStorageConfigResourceTestBa
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonBasicAuthTest.php b/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonBasicAuthTest.php
index e3c2a3fb9c9a4f924371c94c9b9b0538d7d4628e..498589412afe01c34892564869f5437e2e914d9e 100644
--- a/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonBasicAuthTest.php
+++ b/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class FieldStorageConfigHalJsonBasicAuthTest extends FieldStorageConfigResourceT
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonCookieTest.php b/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonCookieTest.php
index 51df45617dfd49885b1b6cd0b3858ff64e45f68b..313e6ba7e269a59ed5e3d55a661f1d7c1deedaa8 100644
--- a/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonCookieTest.php
+++ b/core/modules/field/tests/src/Functional/Hal/FieldStorageConfigHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class FieldStorageConfigHalJsonCookieTest extends FieldStorageConfigResourceTest
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/NestedFormTest.php b/core/modules/field/tests/src/Functional/NestedFormTest.php
index 6ae583ff858e9bfb32aa52ad42eabcbfc2f66b59..31af3d485663e09ead888da981f1addaf39f2ace 100644
--- a/core/modules/field/tests/src/Functional/NestedFormTest.php
+++ b/core/modules/field/tests/src/Functional/NestedFormTest.php
@@ -20,6 +20,11 @@ class NestedFormTest extends FieldTestBase {
    */
   public static $modules = ['field_test', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/field/tests/src/Functional/Number/NumberFieldTest.php b/core/modules/field/tests/src/Functional/Number/NumberFieldTest.php
index 347b72c41904a266c42b458dd1059d30f2ab337c..2df7f41a93b1828f677a651caa0a0638403f0743 100644
--- a/core/modules/field/tests/src/Functional/Number/NumberFieldTest.php
+++ b/core/modules/field/tests/src/Functional/Number/NumberFieldTest.php
@@ -20,6 +20,11 @@ class NumberFieldTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->drupalLogin($this->drupalCreateUser([
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonAnonTest.php b/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonAnonTest.php
index d11e46caf6b8c319c8e316b3e23ad75cdd86b0b6..7fa684d868d8a4acfe5a4aeb3e79175faa82aae5 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonAnonTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonAnonTest.php
@@ -21,4 +21,9 @@ class FieldConfigJsonAnonTest extends FieldConfigResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonBasicAuthTest.php b/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonBasicAuthTest.php
index d27354eac2b38858ab366074a3fb27c0b9ff7563..376c752ee0e65bc2f40f285debfc44fe9ebd8cfe 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonBasicAuthTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FieldConfigJsonBasicAuthTest extends FieldConfigResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonCookieTest.php b/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonCookieTest.php
index 089bd8f29935f8895fcbb57c5ca62b2675b053ff..413fa93fcefd190bb4d56ca3a36ddcfa828d1826 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonCookieTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldConfigJsonCookieTest.php
@@ -26,4 +26,9 @@ class FieldConfigJsonCookieTest extends FieldConfigResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlAnonTest.php b/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlAnonTest.php
index 8809e60e937f26c39a2f44a88fca3ca7a71ecf82..306625ee7e0064c1eb11703a62c3daa02f2d2e00 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlAnonTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlAnonTest.php
@@ -23,4 +23,9 @@ class FieldConfigXmlAnonTest extends FieldConfigResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlBasicAuthTest.php b/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlBasicAuthTest.php
index 109f2dc94ac752aebd239050374f44b647ee7606..13b42d3eab65180092927c62de4b9f1fbd828953 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlBasicAuthTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class FieldConfigXmlBasicAuthTest extends FieldConfigResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlCookieTest.php b/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlCookieTest.php
index d8aebdd1c88e2520691aa41206f6ab6226215f11..77adb16fa582a50f06ccf956137245831c250c4f 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlCookieTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldConfigXmlCookieTest.php
@@ -28,4 +28,9 @@ class FieldConfigXmlCookieTest extends FieldConfigResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonAnonTest.php b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonAnonTest.php
index 5e58c2a933a2e41408db82ebcdb59220b15e4ff6..311dd45011ed52112b1cf6a3fbd57fde5cab812c 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonAnonTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonAnonTest.php
@@ -21,4 +21,9 @@ class FieldStorageConfigJsonAnonTest extends FieldStorageConfigResourceTestBase
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonBasicAuthTest.php b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonBasicAuthTest.php
index 9aa875ab899e16a06f193a31568ec5ed006ac2ca..5256b06203624084b97a46e440a4b10959787369 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonBasicAuthTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FieldStorageConfigJsonBasicAuthTest extends FieldStorageConfigResourceTest
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonCookieTest.php b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonCookieTest.php
index fbcf42b1b948da801484581906c6c87b9011ca57..c61d3eb2c5d0156d4d0e1320202ebd15cfca7d87 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonCookieTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigJsonCookieTest.php
@@ -26,4 +26,9 @@ class FieldStorageConfigJsonCookieTest extends FieldStorageConfigResourceTestBas
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlAnonTest.php b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlAnonTest.php
index 4af918b03f625b0f6845951a1d7f5dd32504b11b..66f3fb040da739483d45b742089e2762e73b59f3 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlAnonTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlAnonTest.php
@@ -23,4 +23,9 @@ class FieldStorageConfigXmlAnonTest extends FieldStorageConfigResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlBasicAuthTest.php b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlBasicAuthTest.php
index d6fe68f8e719fa2c9680471287cbcae869447b9e..cea708147044035942ec3d8075db3ebe06555c1f 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlBasicAuthTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class FieldStorageConfigXmlBasicAuthTest extends FieldStorageConfigResourceTestB
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlCookieTest.php b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlCookieTest.php
index 6672a0df023fba54be3325f4393368bdd8e917cc..38730662ea8cd2ac3348768570f214871c09ff74 100644
--- a/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlCookieTest.php
+++ b/core/modules/field/tests/src/Functional/Rest/FieldStorageConfigXmlCookieTest.php
@@ -28,4 +28,9 @@ class FieldStorageConfigXmlCookieTest extends FieldStorageConfigResourceTestBase
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/field/tests/src/Functional/String/StringFieldTest.php b/core/modules/field/tests/src/Functional/String/StringFieldTest.php
index 21273673913a347cb7f121d63545a813118cf205..d12fd33819d292271f223f688b4fe7bbcb83f425 100644
--- a/core/modules/field/tests/src/Functional/String/StringFieldTest.php
+++ b/core/modules/field/tests/src/Functional/String/StringFieldTest.php
@@ -22,6 +22,11 @@ class StringFieldTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user without any special permissions.
    *
diff --git a/core/modules/field/tests/src/Functional/TranslationWebTest.php b/core/modules/field/tests/src/Functional/TranslationWebTest.php
index 400044bb56f4de96324a01b8967c55cbfecb2135..d15692e1ad66f134a29b51394c1a60b9f1718e94 100644
--- a/core/modules/field/tests/src/Functional/TranslationWebTest.php
+++ b/core/modules/field/tests/src/Functional/TranslationWebTest.php
@@ -21,6 +21,11 @@ class TranslationWebTest extends FieldTestBase {
    */
   public static $modules = ['language', 'field_test', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the field to use in this test.
    *
diff --git a/core/modules/field/tests/src/Functional/Views/FieldUITest.php b/core/modules/field/tests/src/Functional/Views/FieldUITest.php
index f43b30d66294cf57b3417f53d963705ed4674592..8d4feaa341782716aed8bfae65d85272340f36ed 100644
--- a/core/modules/field/tests/src/Functional/Views/FieldUITest.php
+++ b/core/modules/field/tests/src/Functional/Views/FieldUITest.php
@@ -28,6 +28,11 @@ class FieldUITest extends FieldTestBase {
    */
   public static $modules = ['views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with the 'administer views' permission.
    *
diff --git a/core/modules/field/tests/src/Functional/reEnableModuleFieldTest.php b/core/modules/field/tests/src/Functional/reEnableModuleFieldTest.php
index 39fb2dc9b3763a6f17813ded0302c5f055eb33fa..21b91e0ebb1b35da431f8a2e7cd56918acf1e96a 100644
--- a/core/modules/field/tests/src/Functional/reEnableModuleFieldTest.php
+++ b/core/modules/field/tests/src/Functional/reEnableModuleFieldTest.php
@@ -29,6 +29,11 @@ class reEnableModuleFieldTest extends BrowserTestBase {
     'telephone',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/field/tests/src/FunctionalJavascript/Boolean/BooleanFormatterSettingsTest.php b/core/modules/field/tests/src/FunctionalJavascript/Boolean/BooleanFormatterSettingsTest.php
index b6224c0e20cd068b3e213086349c2cf0f26d20a9..9fedc222a88c1bc5a44a8017db23a1354ad8d25a 100644
--- a/core/modules/field/tests/src/FunctionalJavascript/Boolean/BooleanFormatterSettingsTest.php
+++ b/core/modules/field/tests/src/FunctionalJavascript/Boolean/BooleanFormatterSettingsTest.php
@@ -20,6 +20,11 @@ class BooleanFormatterSettingsTest extends WebDriverTestBase {
    */
   public static $modules = ['field', 'field_ui', 'text', 'node', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the entity bundle that is created in the test.
    *
diff --git a/core/modules/field/tests/src/FunctionalJavascript/EntityReference/EntityReferenceAdminTest.php b/core/modules/field/tests/src/FunctionalJavascript/EntityReference/EntityReferenceAdminTest.php
index 7b6fabe488c7aaf8660319359628bb40d36a60fb..170c103c05b9d5079cd935df1e6ce7e97b5d1d35 100644
--- a/core/modules/field/tests/src/FunctionalJavascript/EntityReference/EntityReferenceAdminTest.php
+++ b/core/modules/field/tests/src/FunctionalJavascript/EntityReference/EntityReferenceAdminTest.php
@@ -27,6 +27,11 @@ class EntityReferenceAdminTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'field_ui', 'path', 'taxonomy', 'block', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the content type created for testing purposes.
    *
diff --git a/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php b/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php
index 0561d73711999d99c5ead776ea40bdad0dbd0667..d56a723caf89498d6327ece63749fb76e189a4d4 100644
--- a/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php
+++ b/core/modules/field/tests/src/FunctionalJavascript/FormJSAddMoreTest.php
@@ -20,6 +20,11 @@ class FormJSAddMoreTest extends WebDriverTestBase {
    */
   public static $modules = ['field_test', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php b/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php
index e649e72eeb149aa660a78d71c169706281b7b010..cefa69e38f3537172e55423c1dc23546f6b17bb5 100644
--- a/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php
+++ b/core/modules/field/tests/src/FunctionalJavascript/Number/NumberFieldTest.php
@@ -19,6 +19,11 @@ class NumberFieldTest extends WebDriverTestBase {
    */
   protected static $modules = ['node', 'entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_layout/tests/src/Functional/FieldLayoutTest.php b/core/modules/field_layout/tests/src/Functional/FieldLayoutTest.php
index 9bab0b54312c7edc4730f93f6d24f00efcd22f99..47458e458312d2fa2f54a2ed359c1d7a08fd5d7c 100644
--- a/core/modules/field_layout/tests/src/Functional/FieldLayoutTest.php
+++ b/core/modules/field_layout/tests/src/Functional/FieldLayoutTest.php
@@ -16,6 +16,11 @@ class FieldLayoutTest extends BrowserTestBase {
    */
   public static $modules = ['field_layout', 'field_ui', 'node', 'field_layout_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_layout/tests/src/FunctionalJavascript/FieldLayoutTest.php b/core/modules/field_layout/tests/src/FunctionalJavascript/FieldLayoutTest.php
index 8a36c8489f51954974848b6afa58c139ffa9dca0..9114b93787a5779c6f7522cb168e01ebc9f8aca2 100644
--- a/core/modules/field_layout/tests/src/FunctionalJavascript/FieldLayoutTest.php
+++ b/core/modules/field_layout/tests/src/FunctionalJavascript/FieldLayoutTest.php
@@ -17,6 +17,11 @@ class FieldLayoutTest extends WebDriverTestBase {
    */
   public static $modules = ['field_layout', 'field_ui', 'field_layout_test', 'layout_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/Functional/EntityDisplayModeTest.php b/core/modules/field_ui/tests/src/Functional/EntityDisplayModeTest.php
index 953684193d3cbb4315f1717817ac1e8e2ce98086..2a04bf258f06ccd0215f28240dcfafbe3b3f234d 100644
--- a/core/modules/field_ui/tests/src/Functional/EntityDisplayModeTest.php
+++ b/core/modules/field_ui/tests/src/Functional/EntityDisplayModeTest.php
@@ -21,6 +21,11 @@ class EntityDisplayModeTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'entity_test', 'field_ui', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/Functional/EntityDisplayTest.php b/core/modules/field_ui/tests/src/Functional/EntityDisplayTest.php
index c9cfc052ab506c617ddf1e2d4944725a8b84ca12..d7b63558a358471c93d2348fdb2ad719928ae48e 100644
--- a/core/modules/field_ui/tests/src/Functional/EntityDisplayTest.php
+++ b/core/modules/field_ui/tests/src/Functional/EntityDisplayTest.php
@@ -16,6 +16,11 @@ class EntityDisplayTest extends BrowserTestBase {
    */
   public static $modules = ['field_ui', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/Functional/FieldUIDeleteTest.php b/core/modules/field_ui/tests/src/Functional/FieldUIDeleteTest.php
index 5236905581e486549c55e80e80bd419a47a084c6..ef047f6d4755434649e745dd7992f13c7ad9f31b 100644
--- a/core/modules/field_ui/tests/src/Functional/FieldUIDeleteTest.php
+++ b/core/modules/field_ui/tests/src/Functional/FieldUIDeleteTest.php
@@ -25,6 +25,11 @@ class FieldUIDeleteTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'field_ui', 'field_test', 'block', 'field_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test views to enable
    *
diff --git a/core/modules/field_ui/tests/src/Functional/FieldUIIndentationTest.php b/core/modules/field_ui/tests/src/Functional/FieldUIIndentationTest.php
index 1f66c9a77276398b39773d13c6026529ba49164f..0eeff4bcbdc5f19b480ef801de717230e48bc3b6 100644
--- a/core/modules/field_ui/tests/src/Functional/FieldUIIndentationTest.php
+++ b/core/modules/field_ui/tests/src/Functional/FieldUIIndentationTest.php
@@ -18,6 +18,11 @@ class FieldUIIndentationTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'field_ui', 'field_ui_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/Functional/FieldUIRouteTest.php b/core/modules/field_ui/tests/src/Functional/FieldUIRouteTest.php
index fe7a27011cac469396ec919144451e19932759d9..7bbc546206ee01ab2e76166af51876e615baeefd 100644
--- a/core/modules/field_ui/tests/src/Functional/FieldUIRouteTest.php
+++ b/core/modules/field_ui/tests/src/Functional/FieldUIRouteTest.php
@@ -20,6 +20,11 @@ class FieldUIRouteTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/Functional/ManageDisplayTest.php b/core/modules/field_ui/tests/src/Functional/ManageDisplayTest.php
index aedb63e27d04f535b321dd54395981674758efec..60ab7c03fdbceec20f0382419c909ca402eb8471 100644
--- a/core/modules/field_ui/tests/src/Functional/ManageDisplayTest.php
+++ b/core/modules/field_ui/tests/src/Functional/ManageDisplayTest.php
@@ -27,6 +27,11 @@ class ManageDisplayTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'field_ui', 'taxonomy', 'search', 'field_test', 'field_third_party_test', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/Functional/ManageFieldsFunctionalTest.php b/core/modules/field_ui/tests/src/Functional/ManageFieldsFunctionalTest.php
index bf86b7e98fc4602ea0b4073daf5d48c423d3fb2c..616bedd1b74c028ef7c1242fc579fb12ae15e4b3 100644
--- a/core/modules/field_ui/tests/src/Functional/ManageFieldsFunctionalTest.php
+++ b/core/modules/field_ui/tests/src/Functional/ManageFieldsFunctionalTest.php
@@ -29,6 +29,11 @@ class ManageFieldsFunctionalTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'field_ui', 'field_test', 'taxonomy', 'image', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The ID of the custom content type created for testing.
    *
diff --git a/core/modules/field_ui/tests/src/Functional/ManageFieldsTest.php b/core/modules/field_ui/tests/src/Functional/ManageFieldsTest.php
index 1c21b069b4bc9c8aa11d1a632924e54d20e88d93..c696e58783744f5cd63a83c674733895c48eb268 100644
--- a/core/modules/field_ui/tests/src/Functional/ManageFieldsTest.php
+++ b/core/modules/field_ui/tests/src/Functional/ManageFieldsTest.php
@@ -21,6 +21,11 @@ class ManageFieldsTest extends BrowserTestBase {
     'text',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php b/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php
index 7909f0f0061c61d32fd07976822d7efe657d355d..22c1f1b2c70ced497504ce59de20c545a21324f3 100644
--- a/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php
+++ b/core/modules/field_ui/tests/src/FunctionalJavascript/EntityDisplayTest.php
@@ -17,6 +17,11 @@ class EntityDisplayTest extends WebDriverTestBase {
    */
   public static $modules = ['field_ui', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/field_ui/tests/src/FunctionalJavascript/ManageDisplayTest.php b/core/modules/field_ui/tests/src/FunctionalJavascript/ManageDisplayTest.php
index 404e6ed33e8963584897c20bd79be856ed18f021..45fa8e818e9fe92e4c4b4a9c15075b16392a4dc7 100644
--- a/core/modules/field_ui/tests/src/FunctionalJavascript/ManageDisplayTest.php
+++ b/core/modules/field_ui/tests/src/FunctionalJavascript/ManageDisplayTest.php
@@ -23,6 +23,11 @@ class ManageDisplayTest extends WebDriverTestBase {
     'block',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @var string
    */
diff --git a/core/modules/file/tests/src/Functional/DownloadTest.php b/core/modules/file/tests/src/Functional/DownloadTest.php
index 68ef66c2110c2e9fb27d17aaec68e9d5bce2a7da..133729f4b5602851b496d329e5afac13da559483 100644
--- a/core/modules/file/tests/src/Functional/DownloadTest.php
+++ b/core/modules/file/tests/src/Functional/DownloadTest.php
@@ -11,6 +11,11 @@
  */
 class DownloadTest extends FileManagedTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     // Clear out any hook calls.
diff --git a/core/modules/file/tests/src/Functional/FileFieldAnonymousSubmissionTest.php b/core/modules/file/tests/src/Functional/FileFieldAnonymousSubmissionTest.php
index 70181dac808c66040f8d0db9ce08d1fe57ffbe3e..5e389e2b9793ab55697e0531209cb6c229286da9 100644
--- a/core/modules/file/tests/src/Functional/FileFieldAnonymousSubmissionTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldAnonymousSubmissionTest.php
@@ -13,6 +13,11 @@
  */
 class FileFieldAnonymousSubmissionTest extends FileFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/FileFieldDisplayTest.php b/core/modules/file/tests/src/Functional/FileFieldDisplayTest.php
index 2fa7f51e3ea6982c1fe95a4370a38ec5204cb2ac..922985cb4e3191a56af27ada4da5a194c13bf0e3 100644
--- a/core/modules/file/tests/src/Functional/FileFieldDisplayTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldDisplayTest.php
@@ -14,6 +14,11 @@
  */
 class FileFieldDisplayTest extends FileFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests normal formatter display on node display.
    */
diff --git a/core/modules/file/tests/src/Functional/FileFieldFormatterAccessTest.php b/core/modules/file/tests/src/Functional/FileFieldFormatterAccessTest.php
index 2337861978c7a6e3fd3d00c50c7bcc445f41c898..4dc6aedf5dd201dd51fab4f87f12fb9769061c48 100644
--- a/core/modules/file/tests/src/Functional/FileFieldFormatterAccessTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldFormatterAccessTest.php
@@ -15,6 +15,11 @@ class FileFieldFormatterAccessTest extends FileFieldTestBase {
    */
   public static $modules = ['node', 'file', 'field_ui', 'file_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the custom access handler is invoked.
    */
diff --git a/core/modules/file/tests/src/Functional/FileFieldPathTest.php b/core/modules/file/tests/src/Functional/FileFieldPathTest.php
index 5acc0d9eb42fc4424f8d161c2314df49d99e5577..0a0fa79a573cf2dad99ad724c960b85a0a98e110 100644
--- a/core/modules/file/tests/src/Functional/FileFieldPathTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldPathTest.php
@@ -12,6 +12,11 @@
  */
 class FileFieldPathTest extends FileFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the normal formatter display on node display.
    */
diff --git a/core/modules/file/tests/src/Functional/FileFieldRSSContentTest.php b/core/modules/file/tests/src/Functional/FileFieldRSSContentTest.php
index 57d2fd2363a4b83d90e6875318fd526556d4ff98..73f94047a068c5719a14dc499309c2f271041467 100644
--- a/core/modules/file/tests/src/Functional/FileFieldRSSContentTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldRSSContentTest.php
@@ -18,6 +18,11 @@ class FileFieldRSSContentTest extends FileFieldTestBase {
    */
   public static $modules = ['node', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests RSS enclosure formatter display for RSS feeds.
    */
diff --git a/core/modules/file/tests/src/Functional/FileFieldRevisionTest.php b/core/modules/file/tests/src/Functional/FileFieldRevisionTest.php
index 3214c0b92d9b2f35872515a5edceddc68d115ec2..39136b2f55ec33d3ee4994d0f2c4f1e51f89382d 100644
--- a/core/modules/file/tests/src/Functional/FileFieldRevisionTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldRevisionTest.php
@@ -12,6 +12,11 @@
  */
 class FileFieldRevisionTest extends FileFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests creating multiple revisions of a node and managing attached files.
    *
diff --git a/core/modules/file/tests/src/Functional/FileFieldValidateTest.php b/core/modules/file/tests/src/Functional/FileFieldValidateTest.php
index 5c7b5cfff1a3f6f3a45a8196ef1b98ed6e4b5a7e..5aa059af45fa58040975c87fc2b5bf182430c2e7 100644
--- a/core/modules/file/tests/src/Functional/FileFieldValidateTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldValidateTest.php
@@ -19,6 +19,11 @@ class FileFieldValidateTest extends FileFieldTestBase {
 
   use ExpectDeprecationTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the required property on file fields.
    */
diff --git a/core/modules/file/tests/src/Functional/FileFieldWidgetTest.php b/core/modules/file/tests/src/Functional/FileFieldWidgetTest.php
index 781208a91f033b5471d3962ce10acbd5f3360f70..ff14143a650b9864be8b1c499eadf078b67f8fee 100644
--- a/core/modules/file/tests/src/Functional/FileFieldWidgetTest.php
+++ b/core/modules/file/tests/src/Functional/FileFieldWidgetTest.php
@@ -30,6 +30,11 @@ class FileFieldWidgetTest extends FileFieldTestBase {
    */
   protected static $modules = ['comment', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/FileListingTest.php b/core/modules/file/tests/src/Functional/FileListingTest.php
index 93f2dc8a0502ab784cadd0d187cd30808190eb84..4feffa5d01fb99f9b078c1e9abb12c8850b86334 100644
--- a/core/modules/file/tests/src/Functional/FileListingTest.php
+++ b/core/modules/file/tests/src/Functional/FileListingTest.php
@@ -20,6 +20,11 @@ class FileListingTest extends FileFieldTestBase {
    */
   public static $modules = ['views', 'file', 'image', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An authenticated user.
    *
diff --git a/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php b/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php
index 2b448ba7dbfb9424e26ce4778496e497767bf738..ac9350912c3883a4d7c4fa20b43c7ac4c06c1a9c 100644
--- a/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php
+++ b/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php
@@ -11,6 +11,11 @@
  */
 class FileManagedFileElementTest extends FileFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the managed_file element type.
    */
diff --git a/core/modules/file/tests/src/Functional/FileOnTranslatedEntityTest.php b/core/modules/file/tests/src/Functional/FileOnTranslatedEntityTest.php
index 65aa802b929fe43b934bab6987edea131aa09fd1..7bc1e0a808b57c90d26143841b4ee074d87401bf 100644
--- a/core/modules/file/tests/src/Functional/FileOnTranslatedEntityTest.php
+++ b/core/modules/file/tests/src/Functional/FileOnTranslatedEntityTest.php
@@ -16,6 +16,11 @@ class FileOnTranslatedEntityTest extends FileFieldTestBase {
    */
   public static $modules = ['language', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the file field used in the test.
    *
diff --git a/core/modules/file/tests/src/Functional/FilePrivateTest.php b/core/modules/file/tests/src/Functional/FilePrivateTest.php
index 4b699ef436939c66c1d94e9c52f6909d482b99a6..1ac6d138ea83f8b194127a8521f7187cde4f77bb 100644
--- a/core/modules/file/tests/src/Functional/FilePrivateTest.php
+++ b/core/modules/file/tests/src/Functional/FilePrivateTest.php
@@ -22,6 +22,11 @@ class FilePrivateTest extends FileFieldTestBase {
    */
   public static $modules = ['node_access_test', 'field_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     node_access_test_add_field(NodeType::load('article'));
diff --git a/core/modules/file/tests/src/Functional/FileTokenReplaceTest.php b/core/modules/file/tests/src/Functional/FileTokenReplaceTest.php
index 14759e98569a4d7133cdc8144098da23fb06d728..4b832ac267915e6a32b6b3c940d9dac4aba6adc6 100644
--- a/core/modules/file/tests/src/Functional/FileTokenReplaceTest.php
+++ b/core/modules/file/tests/src/Functional/FileTokenReplaceTest.php
@@ -15,6 +15,11 @@
  */
 class FileTokenReplaceTest extends FileFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Creates a file, then tests the tokens generated from it.
    */
diff --git a/core/modules/file/tests/src/Functional/FileUploadJsonBasicAuthTest.php b/core/modules/file/tests/src/Functional/FileUploadJsonBasicAuthTest.php
index cef59f83cf2efcee4eaa74db13ab2e492a7ff224..49f50f6614a2e7bceb1be42a3b853ffdc9fb76e6 100644
--- a/core/modules/file/tests/src/Functional/FileUploadJsonBasicAuthTest.php
+++ b/core/modules/file/tests/src/Functional/FileUploadJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class FileUploadJsonBasicAuthTest extends FileUploadResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/FileUploadJsonCookieTest.php b/core/modules/file/tests/src/Functional/FileUploadJsonCookieTest.php
index 8f7495a763b16accb23b8ffe3e0311f04ff498dd..726b6fbffd3cd6d3186d64aad2de0e98b0f82c2c 100644
--- a/core/modules/file/tests/src/Functional/FileUploadJsonCookieTest.php
+++ b/core/modules/file/tests/src/Functional/FileUploadJsonCookieTest.php
@@ -12,6 +12,11 @@ class FileUploadJsonCookieTest extends FileUploadResourceTestBase {
 
   use CookieResourceTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/Formatter/FileAudioFormatterTest.php b/core/modules/file/tests/src/Functional/Formatter/FileAudioFormatterTest.php
index 2de18a294d0ec902869aaec6cdb511e956884df9..4ec5bc3447eda636a84d744a8a44db346599b111 100644
--- a/core/modules/file/tests/src/Functional/Formatter/FileAudioFormatterTest.php
+++ b/core/modules/file/tests/src/Functional/Formatter/FileAudioFormatterTest.php
@@ -11,6 +11,11 @@
  */
 class FileAudioFormatterTest extends FileMediaFormatterTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @covers ::viewElements
    *
diff --git a/core/modules/file/tests/src/Functional/Formatter/FileVideoFormatterTest.php b/core/modules/file/tests/src/Functional/Formatter/FileVideoFormatterTest.php
index 8517b3244d69b3a003d3b06c858d018458e3696b..ec1ca79199fa2b09abfc792d2dff96044b450b8e 100644
--- a/core/modules/file/tests/src/Functional/Formatter/FileVideoFormatterTest.php
+++ b/core/modules/file/tests/src/Functional/Formatter/FileVideoFormatterTest.php
@@ -11,6 +11,11 @@
  */
 class FileVideoFormatterTest extends FileMediaFormatterTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @covers ::viewElements
    *
diff --git a/core/modules/file/tests/src/Functional/Hal/FileHalJsonAnonTest.php b/core/modules/file/tests/src/Functional/Hal/FileHalJsonAnonTest.php
index 6a1310078caa0abee2eda5ff797908be90ef48d6..ca4fcf551afaf8b6c6a919d50ad7a9f3685bcaac 100644
--- a/core/modules/file/tests/src/Functional/Hal/FileHalJsonAnonTest.php
+++ b/core/modules/file/tests/src/Functional/Hal/FileHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class FileHalJsonAnonTest extends FileResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/Hal/FileHalJsonBasicAuthTest.php b/core/modules/file/tests/src/Functional/Hal/FileHalJsonBasicAuthTest.php
index 910107172821f5c3b4f872f62cba694474ccd206..5fbf7678eb7889782a5970a96d37fb348c479c62 100644
--- a/core/modules/file/tests/src/Functional/Hal/FileHalJsonBasicAuthTest.php
+++ b/core/modules/file/tests/src/Functional/Hal/FileHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FileHalJsonBasicAuthTest extends FileHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/Hal/FileHalJsonCookieTest.php b/core/modules/file/tests/src/Functional/Hal/FileHalJsonCookieTest.php
index 7069e9b964f590c51cfc2a248a5e7c7fa10b7301..47abaf3a3c010c165f602662634601ea69d3b6fb 100644
--- a/core/modules/file/tests/src/Functional/Hal/FileHalJsonCookieTest.php
+++ b/core/modules/file/tests/src/Functional/Hal/FileHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class FileHalJsonCookieTest extends FileHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonBasicAuthTest.php b/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonBasicAuthTest.php
index 647b85b9d65faceb3734c06ba133a8ff09564b8b..7cb3fb256b3e0ff046cd848075edb0529c1cd940 100644
--- a/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonBasicAuthTest.php
+++ b/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FileUploadHalJsonBasicAuthTest extends FileUploadHalJsonTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonCookieTest.php b/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonCookieTest.php
index 510b6acfb97672045a835b1da0aecb67e4126e87..b9937c09a51223f3760cf1d0256ec1abb6e80875 100644
--- a/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonCookieTest.php
+++ b/core/modules/file/tests/src/Functional/Hal/FileUploadHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class FileUploadHalJsonCookieTest extends FileUploadHalJsonTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/file/tests/src/Functional/MultipleFileUploadTest.php b/core/modules/file/tests/src/Functional/MultipleFileUploadTest.php
index 7ed5ccdcc10839e60fec95ece3ff0e4b86a8e426..8817a66d9c4c126097a94b4900bdad07fec64651 100644
--- a/core/modules/file/tests/src/Functional/MultipleFileUploadTest.php
+++ b/core/modules/file/tests/src/Functional/MultipleFileUploadTest.php
@@ -16,6 +16,11 @@ class MultipleFileUploadTest extends BrowserTestBase {
    */
   public static $modules = ['file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/PrivateFileOnTranslatedEntityTest.php b/core/modules/file/tests/src/Functional/PrivateFileOnTranslatedEntityTest.php
index 44b2ee10c9c70ac77329ac206b8312c6240a37ed..a838efef66fa9b96869333b0b38d6e426e4ed182 100644
--- a/core/modules/file/tests/src/Functional/PrivateFileOnTranslatedEntityTest.php
+++ b/core/modules/file/tests/src/Functional/PrivateFileOnTranslatedEntityTest.php
@@ -17,6 +17,11 @@ class PrivateFileOnTranslatedEntityTest extends FileFieldTestBase {
    */
   public static $modules = ['language', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the file field used in the test.
    *
diff --git a/core/modules/file/tests/src/Functional/RemoteFileSaveUploadTest.php b/core/modules/file/tests/src/Functional/RemoteFileSaveUploadTest.php
index e0e4be4b3cc26a21a1c773c4db6c54a4f456eb88..91a909fd8c8827fcb3949bd1447cc4ae6bd117e6 100644
--- a/core/modules/file/tests/src/Functional/RemoteFileSaveUploadTest.php
+++ b/core/modules/file/tests/src/Functional/RemoteFileSaveUploadTest.php
@@ -16,6 +16,11 @@ class RemoteFileSaveUploadTest extends SaveUploadTest {
    */
   public static $modules = ['file_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->config('system.file')->set('default_scheme', 'dummy-remote')->save();
diff --git a/core/modules/file/tests/src/Functional/Rest/FileJsonAnonTest.php b/core/modules/file/tests/src/Functional/Rest/FileJsonAnonTest.php
index 5d76ea24735cf76a49770c4ae71327bb8a8f40f5..9df9bc8489d4f896303308d1152e7a98c4e3cc84 100644
--- a/core/modules/file/tests/src/Functional/Rest/FileJsonAnonTest.php
+++ b/core/modules/file/tests/src/Functional/Rest/FileJsonAnonTest.php
@@ -21,4 +21,9 @@ class FileJsonAnonTest extends FileResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/file/tests/src/Functional/Rest/FileJsonBasicAuthTest.php b/core/modules/file/tests/src/Functional/Rest/FileJsonBasicAuthTest.php
index 87a65ac359d79dbd0e7abcb90c9a7da454a7a4b1..a327a0d9d7ad08610dd1a540090a1fa022aa490d 100644
--- a/core/modules/file/tests/src/Functional/Rest/FileJsonBasicAuthTest.php
+++ b/core/modules/file/tests/src/Functional/Rest/FileJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FileJsonBasicAuthTest extends FileResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/Rest/FileJsonCookieTest.php b/core/modules/file/tests/src/Functional/Rest/FileJsonCookieTest.php
index 9c797207dcd1a65288f200721e98b55215f65891..8ca3fe1efa7d22872a02d64bcb34c97f596072a9 100644
--- a/core/modules/file/tests/src/Functional/Rest/FileJsonCookieTest.php
+++ b/core/modules/file/tests/src/Functional/Rest/FileJsonCookieTest.php
@@ -26,4 +26,9 @@ class FileJsonCookieTest extends FileResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/file/tests/src/Functional/Rest/FileXmlAnonTest.php b/core/modules/file/tests/src/Functional/Rest/FileXmlAnonTest.php
index 8360096fb9b5590d39dac3d48bffcfbb00460865..d14cc48670ac7d5a8a4c58e132af91aa44289e5c 100644
--- a/core/modules/file/tests/src/Functional/Rest/FileXmlAnonTest.php
+++ b/core/modules/file/tests/src/Functional/Rest/FileXmlAnonTest.php
@@ -23,4 +23,9 @@ class FileXmlAnonTest extends FileResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/file/tests/src/Functional/Rest/FileXmlBasicAuthTest.php b/core/modules/file/tests/src/Functional/Rest/FileXmlBasicAuthTest.php
index 66e9986dbc0fb0627100f203daa6bf5e007dff75..e0e0030239bedb6205d4b5d0c3779951456742c6 100644
--- a/core/modules/file/tests/src/Functional/Rest/FileXmlBasicAuthTest.php
+++ b/core/modules/file/tests/src/Functional/Rest/FileXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class FileXmlBasicAuthTest extends FileResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/Functional/Rest/FileXmlCookieTest.php b/core/modules/file/tests/src/Functional/Rest/FileXmlCookieTest.php
index 4b7db031e50b2d7dbcc969caa909fb4e00cabb99..308f0247f90e26d7e843b6f6195fdb91fe00e670 100644
--- a/core/modules/file/tests/src/Functional/Rest/FileXmlCookieTest.php
+++ b/core/modules/file/tests/src/Functional/Rest/FileXmlCookieTest.php
@@ -28,4 +28,9 @@ class FileXmlCookieTest extends FileResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/file/tests/src/Functional/SaveUploadFormTest.php b/core/modules/file/tests/src/Functional/SaveUploadFormTest.php
index de1a4ff0157ee8606cad301189214b84125706e1..b4d7676d198f90b74fc15284ad7957237d35e9db 100644
--- a/core/modules/file/tests/src/Functional/SaveUploadFormTest.php
+++ b/core/modules/file/tests/src/Functional/SaveUploadFormTest.php
@@ -26,6 +26,11 @@ class SaveUploadFormTest extends FileManagedTestBase {
    */
   public static $modules = ['dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * An image file path for uploading.
    *
diff --git a/core/modules/file/tests/src/Functional/SaveUploadTest.php b/core/modules/file/tests/src/Functional/SaveUploadTest.php
index 920b4fe139da8c856995a3c5881a64f3eb12d531..8e5c1f1ae636ca689f61ec2dff9f64ed4c256c55 100644
--- a/core/modules/file/tests/src/Functional/SaveUploadTest.php
+++ b/core/modules/file/tests/src/Functional/SaveUploadTest.php
@@ -26,6 +26,11 @@ class SaveUploadTest extends FileManagedTestBase {
    */
   public static $modules = ['dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An image file path for uploading.
    *
diff --git a/core/modules/file/tests/src/Functional/Views/RelationshipUserFileDataTest.php b/core/modules/file/tests/src/Functional/Views/RelationshipUserFileDataTest.php
index 887b6384fac46048d120cf3c591574b7d9649b86..8f8580d23e7ecf116d2deb1185a603b83c181129 100644
--- a/core/modules/file/tests/src/Functional/Views/RelationshipUserFileDataTest.php
+++ b/core/modules/file/tests/src/Functional/Views/RelationshipUserFileDataTest.php
@@ -23,6 +23,11 @@ class RelationshipUserFileDataTest extends ViewTestBase {
    */
   public static $modules = ['file', 'file_test_views', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/file/tests/src/FunctionalJavascript/AjaxFileManagedMultipleTest.php b/core/modules/file/tests/src/FunctionalJavascript/AjaxFileManagedMultipleTest.php
index c4165a8b3398ac6f9497868ac79034647973ce11..9dc76650137c1b1d49ab5e24a8c6dc6def92418d 100644
--- a/core/modules/file/tests/src/FunctionalJavascript/AjaxFileManagedMultipleTest.php
+++ b/core/modules/file/tests/src/FunctionalJavascript/AjaxFileManagedMultipleTest.php
@@ -22,6 +22,11 @@ class AjaxFileManagedMultipleTest extends WebDriverTestBase {
    */
   protected static $modules = ['file_test', 'file', 'file_module_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test if managed file form element works well with multiple files upload.
    */
diff --git a/core/modules/file/tests/src/FunctionalJavascript/FileFieldValidateTest.php b/core/modules/file/tests/src/FunctionalJavascript/FileFieldValidateTest.php
index 99acc3712a01d7301a519e70ed7f57c49716823b..afbccbbcdde05afe0857572d04c7a950c261b5c0 100644
--- a/core/modules/file/tests/src/FunctionalJavascript/FileFieldValidateTest.php
+++ b/core/modules/file/tests/src/FunctionalJavascript/FileFieldValidateTest.php
@@ -22,6 +22,11 @@ class FileFieldValidateTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test the validation message is displayed only once for ajax uploads.
    */
diff --git a/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php b/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php
index c0d2fc53e04f71d7248f34e859fd2a741f7bb11a..b24b381369d2241c851859e1b7b1ce5b968b1697 100644
--- a/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php
+++ b/core/modules/file/tests/src/FunctionalJavascript/FileFieldWidgetTest.php
@@ -32,6 +32,11 @@ class FileFieldWidgetTest extends WebDriverTestBase {
    */
   protected static $modules = ['node', 'file', 'file_module_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/file/tests/src/FunctionalJavascript/FileManagedFileElementTest.php b/core/modules/file/tests/src/FunctionalJavascript/FileManagedFileElementTest.php
index 5ef877b4d0481b7ec383c76f1fd73d3d3453c1fd..a4f2c0ca55a43cdb2ef7de51f139a3e56ab2f776 100644
--- a/core/modules/file/tests/src/FunctionalJavascript/FileManagedFileElementTest.php
+++ b/core/modules/file/tests/src/FunctionalJavascript/FileManagedFileElementTest.php
@@ -16,6 +16,11 @@ class FileManagedFileElementTest extends WebDriverTestBase {
    */
   protected static $modules = ['node', 'file', 'file_module_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administration permissions.
    *
diff --git a/core/modules/file/tests/src/FunctionalJavascript/MaximumFileSizeExceededUploadTest.php b/core/modules/file/tests/src/FunctionalJavascript/MaximumFileSizeExceededUploadTest.php
index 45c8bf5eec0871051498de5c4186c6a17e4e9dd8..69660365a787b917d02558c1e13dae00e7f8e78e 100644
--- a/core/modules/file/tests/src/FunctionalJavascript/MaximumFileSizeExceededUploadTest.php
+++ b/core/modules/file/tests/src/FunctionalJavascript/MaximumFileSizeExceededUploadTest.php
@@ -22,6 +22,11 @@ class MaximumFileSizeExceededUploadTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The file system service.
    *
diff --git a/core/modules/filter/tests/src/Functional/FilterAdminTest.php b/core/modules/filter/tests/src/Functional/FilterAdminTest.php
index 73289e4cd563e1d4d8324964547a48966c5ff4ec..ece059a3e8150c6b65d33f3c239135c067bc25e5 100644
--- a/core/modules/filter/tests/src/Functional/FilterAdminTest.php
+++ b/core/modules/filter/tests/src/Functional/FilterAdminTest.php
@@ -22,6 +22,11 @@ class FilterAdminTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'filter', 'node', 'filter_test_plugin', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * An user with administration permissions.
    *
diff --git a/core/modules/filter/tests/src/Functional/FilterDefaultFormatTest.php b/core/modules/filter/tests/src/Functional/FilterDefaultFormatTest.php
index e5a57482a53026870f746098b6a2b747aca53653..d74a14dc6fe85b5a689c2383110953b585f0e57c 100644
--- a/core/modules/filter/tests/src/Functional/FilterDefaultFormatTest.php
+++ b/core/modules/filter/tests/src/Functional/FilterDefaultFormatTest.php
@@ -19,6 +19,11 @@ class FilterDefaultFormatTest extends BrowserTestBase {
    */
   public static $modules = ['filter'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if the default text format is accessible to users.
    */
diff --git a/core/modules/filter/tests/src/Functional/FilterFormTest.php b/core/modules/filter/tests/src/Functional/FilterFormTest.php
index 89b4713ac14317258c640cd397d6a3a84543be30..3eb5ae3f83799aa797107ef2f1f6200ae80ca761 100644
--- a/core/modules/filter/tests/src/Functional/FilterFormTest.php
+++ b/core/modules/filter/tests/src/Functional/FilterFormTest.php
@@ -20,6 +20,11 @@ class FilterFormTest extends BrowserTestBase {
    */
   protected static $modules = ['filter', 'filter_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An administrative user account that can administer text formats.
    *
diff --git a/core/modules/filter/tests/src/Functional/FilterFormatAccessTest.php b/core/modules/filter/tests/src/Functional/FilterFormatAccessTest.php
index f82d258ddfc48f93dcbe7d6a2711e4bbab772513..c6ef59b69fbeda2d628f619b6709e92612dcfb21 100644
--- a/core/modules/filter/tests/src/Functional/FilterFormatAccessTest.php
+++ b/core/modules/filter/tests/src/Functional/FilterFormatAccessTest.php
@@ -21,6 +21,11 @@ class FilterFormatAccessTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'filter', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administrative permissions.
    *
diff --git a/core/modules/filter/tests/src/Functional/FilterHooksTest.php b/core/modules/filter/tests/src/Functional/FilterHooksTest.php
index 420a7b3855601b84cdaa110ecd7c16ae8b81ef95..a70a95f96502a9c103985721fffda6b06f54ee1f 100644
--- a/core/modules/filter/tests/src/Functional/FilterHooksTest.php
+++ b/core/modules/filter/tests/src/Functional/FilterHooksTest.php
@@ -19,6 +19,11 @@ class FilterHooksTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'filter_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests hooks on format management.
    *
diff --git a/core/modules/filter/tests/src/Functional/FilterHtmlImageSecureTest.php b/core/modules/filter/tests/src/Functional/FilterHtmlImageSecureTest.php
index 60ccbc5cc64d2e13d7258a42175565592b2cf519..148af99bf9bf6ba02b22873675cd6aebe7357bd4 100644
--- a/core/modules/filter/tests/src/Functional/FilterHtmlImageSecureTest.php
+++ b/core/modules/filter/tests/src/Functional/FilterHtmlImageSecureTest.php
@@ -26,6 +26,11 @@ class FilterHtmlImageSecureTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'node', 'comment'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An authenticated user.
    *
diff --git a/core/modules/filter/tests/src/Functional/FilterSecurityTest.php b/core/modules/filter/tests/src/Functional/FilterSecurityTest.php
index 4a5b7c49d28e85986f680f53b9d86ee04ce5ef3d..103c6e3cde8513229305b1561660b4a5112a8d52 100644
--- a/core/modules/filter/tests/src/Functional/FilterSecurityTest.php
+++ b/core/modules/filter/tests/src/Functional/FilterSecurityTest.php
@@ -23,6 +23,11 @@ class FilterSecurityTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'filter_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administrative permissions.
    *
diff --git a/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonAnonTest.php b/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonAnonTest.php
index 3a7c6335f563fe50c0af3eed48f8cb2b80b8c2b0..8e59a6820d532eb2f182cf03d1cdc7853b92c0cc 100644
--- a/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonAnonTest.php
+++ b/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class FilterFormatHalJsonAnonTest extends FilterFormatResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonBasicAuthTest.php b/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonBasicAuthTest.php
index c76293d9cc33026b557aa7078445442424a8f5e4..00a320cfa54a702d4470a6605779042d0f7efaf1 100644
--- a/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonBasicAuthTest.php
+++ b/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class FilterFormatHalJsonBasicAuthTest extends FilterFormatResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonCookieTest.php b/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonCookieTest.php
index d2a8654c593d978c0b88e2abfc27511145be94b2..262d0449aac6d70c47ca41339f05afec4294cef1 100644
--- a/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonCookieTest.php
+++ b/core/modules/filter/tests/src/Functional/Hal/FilterFormatHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class FilterFormatHalJsonCookieTest extends FilterFormatResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonAnonTest.php b/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonAnonTest.php
index 772ccab6ac7509984d01fba2c86d37f662b45cdc..f6aaad0bae130749214f289a09500947f1013ddd 100644
--- a/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonAnonTest.php
+++ b/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonAnonTest.php
@@ -21,4 +21,9 @@ class FilterFormatJsonAnonTest extends FilterFormatResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonBasicAuthTest.php b/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonBasicAuthTest.php
index 53ba6ce895a7fc045e23af7876c3daa0f6a287c3..10267cf2d2b891dd958ed7996f76886a63b7004a 100644
--- a/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonBasicAuthTest.php
+++ b/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class FilterFormatJsonBasicAuthTest extends FilterFormatResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonCookieTest.php b/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonCookieTest.php
index 432142a7704b9b1e413f528fa7273a295f197e78..5445fa3e72269d07c34fac67d7e23d3e4d8b0469 100644
--- a/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonCookieTest.php
+++ b/core/modules/filter/tests/src/Functional/Rest/FilterFormatJsonCookieTest.php
@@ -26,4 +26,9 @@ class FilterFormatJsonCookieTest extends FilterFormatResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlAnonTest.php b/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlAnonTest.php
index 25b84cf621e946f4ac0b7b2357a49d59a9facfdf..3007fb5f42d573f84d9b87813b526af54445750b 100644
--- a/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlAnonTest.php
+++ b/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlAnonTest.php
@@ -23,4 +23,9 @@ class FilterFormatXmlAnonTest extends FilterFormatResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlBasicAuthTest.php b/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlBasicAuthTest.php
index 6c0c62d52b7832e0a5e7df4b21dcbd9aa05a4cc7..8f2c5be0db62004d5d19acc4b468e8afcfce96aa 100644
--- a/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlBasicAuthTest.php
+++ b/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class FilterFormatXmlBasicAuthTest extends FilterFormatResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlCookieTest.php b/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlCookieTest.php
index 1c3be314dd01b6ffcf062c6212134ba2bc8eff74..e79011a551596e2b08abe5fca0699b9599ea5f7d 100644
--- a/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlCookieTest.php
+++ b/core/modules/filter/tests/src/Functional/Rest/FilterFormatXmlCookieTest.php
@@ -28,4 +28,9 @@ class FilterFormatXmlCookieTest extends FilterFormatResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/forum/tests/src/Functional/ForumBlockTest.php b/core/modules/forum/tests/src/Functional/ForumBlockTest.php
index 5bbe1998ee19fb60b45961df0a06451392e9ddc6..a5043fe26586e652991753ed0cb88573bbe1385a 100644
--- a/core/modules/forum/tests/src/Functional/ForumBlockTest.php
+++ b/core/modules/forum/tests/src/Functional/ForumBlockTest.php
@@ -21,6 +21,11 @@ class ForumBlockTest extends BrowserTestBase {
    */
   public static $modules = ['forum', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with various administrative privileges.
    */
diff --git a/core/modules/forum/tests/src/Functional/ForumIndexTest.php b/core/modules/forum/tests/src/Functional/ForumIndexTest.php
index 5d0ccdff3a70a723234611347e8e401807c44050..3bb803a971c83e6bbb76faeccc6d9c2a6a50ab09 100644
--- a/core/modules/forum/tests/src/Functional/ForumIndexTest.php
+++ b/core/modules/forum/tests/src/Functional/ForumIndexTest.php
@@ -18,6 +18,11 @@ class ForumIndexTest extends BrowserTestBase {
    */
   public static $modules = ['taxonomy', 'comment', 'forum'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/forum/tests/src/Functional/ForumNodeAccessTest.php b/core/modules/forum/tests/src/Functional/ForumNodeAccessTest.php
index 9849084c6cd642a39237caa8256ee0c89faacff0..212bbdd2b5f7ff1b99e187223094652d1b957d54 100644
--- a/core/modules/forum/tests/src/Functional/ForumNodeAccessTest.php
+++ b/core/modules/forum/tests/src/Functional/ForumNodeAccessTest.php
@@ -19,6 +19,11 @@ class ForumNodeAccessTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'comment', 'forum', 'taxonomy', 'tracker', 'node_access_test', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     node_access_rebuild();
diff --git a/core/modules/forum/tests/src/Functional/ForumTest.php b/core/modules/forum/tests/src/Functional/ForumTest.php
index d8417ffd042c72398d1d93596411ee660eda86ba..d906baf2789011a53c3b5d007db5dab452c9ace2 100644
--- a/core/modules/forum/tests/src/Functional/ForumTest.php
+++ b/core/modules/forum/tests/src/Functional/ForumTest.php
@@ -28,6 +28,11 @@ class ForumTest extends BrowserTestBase {
    */
   public static $modules = ['taxonomy', 'comment', 'forum', 'node', 'block', 'menu_ui', 'help'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with various administrative privileges.
    */
diff --git a/core/modules/forum/tests/src/Functional/ForumUninstallTest.php b/core/modules/forum/tests/src/Functional/ForumUninstallTest.php
index 6214bba8f72c9a652cfb7ee0c0e8bc27706f50db..84c81c89337704a10315009df88b48dbae9d1577 100644
--- a/core/modules/forum/tests/src/Functional/ForumUninstallTest.php
+++ b/core/modules/forum/tests/src/Functional/ForumUninstallTest.php
@@ -23,6 +23,11 @@ class ForumUninstallTest extends BrowserTestBase {
    */
   public static $modules = ['forum'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if forum module uninstallation properly deletes the field.
    */
diff --git a/core/modules/forum/tests/src/Functional/Views/ForumIntegrationTest.php b/core/modules/forum/tests/src/Functional/Views/ForumIntegrationTest.php
index 838bee047cabe95a719cce63e7f7fc6e52a01270..eda9006f9e1d30d8ef58863aa15daf7b17db19a6 100644
--- a/core/modules/forum/tests/src/Functional/Views/ForumIntegrationTest.php
+++ b/core/modules/forum/tests/src/Functional/Views/ForumIntegrationTest.php
@@ -21,6 +21,11 @@ class ForumIntegrationTest extends ViewTestBase {
    */
   public static $modules = ['forum_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/help/tests/src/Functional/ExperimentalHelpTest.php b/core/modules/help/tests/src/Functional/ExperimentalHelpTest.php
index 0eabbda56ba5a252ef348f9a254337f6920cd608..ab8d2aca2fb78df476ba4a131509af1c78982bed 100644
--- a/core/modules/help/tests/src/Functional/ExperimentalHelpTest.php
+++ b/core/modules/help/tests/src/Functional/ExperimentalHelpTest.php
@@ -21,6 +21,11 @@ class ExperimentalHelpTest extends BrowserTestBase {
    */
   public static $modules = ['help', 'experimental_module_test', 'help_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The admin user.
    *
diff --git a/core/modules/help/tests/src/Functional/HelpBlockTest.php b/core/modules/help/tests/src/Functional/HelpBlockTest.php
index 81c4fc15329a69776d3691a8ea9a7dc70f90a551..f4f8db5b1391a225e95c6b1df5c1cbd05b04f752 100644
--- a/core/modules/help/tests/src/Functional/HelpBlockTest.php
+++ b/core/modules/help/tests/src/Functional/HelpBlockTest.php
@@ -16,6 +16,11 @@ class HelpBlockTest extends BrowserTestBase {
    */
   public static $modules = ['help', 'help_page_test', 'block', 'more_help_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The help block instance.
    *
diff --git a/core/modules/help/tests/src/Functional/HelpPageOrderTest.php b/core/modules/help/tests/src/Functional/HelpPageOrderTest.php
index 2981568b6ededdd21e7749aa39511ad5a83b5efb..0015ff26fb3c8a346db723daad2715581728d71e 100644
--- a/core/modules/help/tests/src/Functional/HelpPageOrderTest.php
+++ b/core/modules/help/tests/src/Functional/HelpPageOrderTest.php
@@ -16,6 +16,11 @@ class HelpPageOrderTest extends BrowserTestBase {
    */
   protected static $modules = ['help', 'tour'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Strings to search for on admin/help, in order.
    *
diff --git a/core/modules/help/tests/src/Functional/HelpPageReverseOrderTest.php b/core/modules/help/tests/src/Functional/HelpPageReverseOrderTest.php
index 3920b76fcd37d7fda476750532afa9b869ce5317..d31471da9bd6822b3beb5f9e65cbf4cca5eef4cf 100644
--- a/core/modules/help/tests/src/Functional/HelpPageReverseOrderTest.php
+++ b/core/modules/help/tests/src/Functional/HelpPageReverseOrderTest.php
@@ -14,6 +14,11 @@ class HelpPageReverseOrderTest extends HelpPageOrderTest {
    */
   protected static $modules = ['more_help_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Strings to search for on admin/help, in order.
    *
diff --git a/core/modules/help/tests/src/Functional/HelpTest.php b/core/modules/help/tests/src/Functional/HelpTest.php
index 608263d4c9dcce9c51b7ffe05ef8ecb377b21bb8..c78d18cf6f3e4bacd92f5b64c22dcfb6fe243956 100644
--- a/core/modules/help/tests/src/Functional/HelpTest.php
+++ b/core/modules/help/tests/src/Functional/HelpTest.php
@@ -23,6 +23,11 @@ class HelpTest extends BrowserTestBase {
    */
   public static $modules = ['help_test', 'help_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Use the Standard profile to test help implementations of many core modules.
    *
diff --git a/core/modules/help/tests/src/Functional/NoHelpTest.php b/core/modules/help/tests/src/Functional/NoHelpTest.php
index 5df945e35cd059c284119b05f1df189fad29b906..0b68c0d225eb8ff1af195e6cf493738c93c1ef5f 100644
--- a/core/modules/help/tests/src/Functional/NoHelpTest.php
+++ b/core/modules/help/tests/src/Functional/NoHelpTest.php
@@ -20,6 +20,11 @@ class NoHelpTest extends BrowserTestBase {
    */
   public static $modules = ['help', 'menu_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The user who will be created.
    */
diff --git a/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php b/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php
index a886167700bc1b5f627659b8fd399d2094e0ffa0..2f6765c1519a37ea7ce45fd9d150dc56462060aa 100644
--- a/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php
+++ b/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php
@@ -23,6 +23,11 @@ class HelpTopicSearchTest extends HelpTopicTranslatedTestBase {
     'language',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php b/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php
index 957021cf6a6c3ad499b9c9b2f274c5b355321c0e..3dcbbd21c3121f9dffca3159305021e1ac23dad6 100644
--- a/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php
+++ b/core/modules/help_topics/tests/src/Functional/HelpTopicTest.php
@@ -25,6 +25,11 @@ class HelpTopicTest extends BrowserTestBase {
     'block',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The admin user that will be created.
    *
diff --git a/core/modules/help_topics/tests/src/Functional/HelpTopicTranslationTest.php b/core/modules/help_topics/tests/src/Functional/HelpTopicTranslationTest.php
index ead7df35715f19e564a243aafa702c9703e441c6..5a45c8c65bf11cd416c8a784288e6d84e130fdf6 100644
--- a/core/modules/help_topics/tests/src/Functional/HelpTopicTranslationTest.php
+++ b/core/modules/help_topics/tests/src/Functional/HelpTopicTranslationTest.php
@@ -9,6 +9,11 @@
  */
 class HelpTopicTranslationTest extends HelpTopicTranslatedTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/help_topics/tests/src/Functional/HelpTopicsSyntaxTest.php b/core/modules/help_topics/tests/src/Functional/HelpTopicsSyntaxTest.php
index b7204cab0a112378ec0c6cab0d5addbee74cad8f..6127dd4e8c5e644fc958ba0d353de65755f64dc0 100644
--- a/core/modules/help_topics/tests/src/Functional/HelpTopicsSyntaxTest.php
+++ b/core/modules/help_topics/tests/src/Functional/HelpTopicsSyntaxTest.php
@@ -30,6 +30,11 @@ class HelpTopicsSyntaxTest extends BrowserTestBase {
     'help_topics',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests that all Core help topics can be rendered and have good syntax.
    */
diff --git a/core/modules/history/tests/src/Functional/HistoryTest.php b/core/modules/history/tests/src/Functional/HistoryTest.php
index 415541ed60f7cd2b3aca9eff7d2e3e6c8dc81d92..e6c681620c3ba9023b5ec50c8dfcc8fb09fa75f1 100644
--- a/core/modules/history/tests/src/Functional/HistoryTest.php
+++ b/core/modules/history/tests/src/Functional/HistoryTest.php
@@ -23,6 +23,11 @@ class HistoryTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'history'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The main user for testing.
    *
diff --git a/core/modules/image/tests/src/Functional/FileMoveTest.php b/core/modules/image/tests/src/Functional/FileMoveTest.php
index fd253635822635398e47fca0a66be242801a5636..c2a3a1bbe4c944122c75059e15afee4de3954b3a 100644
--- a/core/modules/image/tests/src/Functional/FileMoveTest.php
+++ b/core/modules/image/tests/src/Functional/FileMoveTest.php
@@ -27,6 +27,11 @@ class FileMoveTest extends BrowserTestBase {
    */
   public static $modules = ['image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests moving a randomly generated image.
    */
diff --git a/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonAnonTest.php b/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonAnonTest.php
index 61da51f7d0eca5a58c150f45ca5304a8980443f7..a010f68f0b0c188b60ddba8860b8e4eb1fe1287e 100644
--- a/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonAnonTest.php
+++ b/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ImageStyleHalJsonAnonTest extends ImageStyleResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonBasicAuthTest.php b/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonBasicAuthTest.php
index a6ff4941a37aea66acc6db324adca3c8b402d863..74a351663f46588e96b38c07fe64bd0f2236f5cd 100644
--- a/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonBasicAuthTest.php
+++ b/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class ImageStyleHalJsonBasicAuthTest extends ImageStyleResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonCookieTest.php b/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonCookieTest.php
index 731e356c92290303522015288ef16f5e974edc04..e899b6d13efdc2283c331cdba233c5f5cd871f1c 100644
--- a/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonCookieTest.php
+++ b/core/modules/image/tests/src/Functional/Hal/ImageStyleHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ImageStyleHalJsonCookieTest extends ImageStyleResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/Functional/ImageAdminStylesTest.php b/core/modules/image/tests/src/Functional/ImageAdminStylesTest.php
index 30b600bdf149a9cfd03267b393e20bd2f591fbd4..989a063fb234324a18063e3f2d97096f1d1b5b40 100644
--- a/core/modules/image/tests/src/Functional/ImageAdminStylesTest.php
+++ b/core/modules/image/tests/src/Functional/ImageAdminStylesTest.php
@@ -23,6 +23,11 @@ class ImageAdminStylesTest extends ImageFieldTestBase {
     compareFiles as drupalCompareFiles;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Given an image style, generate an image.
    */
diff --git a/core/modules/image/tests/src/Functional/ImageDimensionsTest.php b/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
index 4c80bb1774fcd912de746e0ff003ba96b393daa3..6a969e5720a7858e948487d05baeb01a9bcb44c0 100644
--- a/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
+++ b/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
@@ -26,6 +26,11 @@ class ImageDimensionsTest extends BrowserTestBase {
    */
   public static $modules = ['image', 'image_module_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected $profile = 'testing';
 
   /**
diff --git a/core/modules/image/tests/src/Functional/ImageEffectsTest.php b/core/modules/image/tests/src/Functional/ImageEffectsTest.php
index f6b4ab36e92f2a95fba0dc5499e682a110a88726..08713f0057a51cbba2c96b40e33e98f22547f686 100644
--- a/core/modules/image/tests/src/Functional/ImageEffectsTest.php
+++ b/core/modules/image/tests/src/Functional/ImageEffectsTest.php
@@ -19,6 +19,11 @@ class ImageEffectsTest extends ToolkitTestBase {
    */
   public static $modules = ['image', 'image_test', 'image_module_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The image effect manager.
    *
diff --git a/core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php b/core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
index 34d05c27283f6fe039a07a8af0a1e6bba8ffd872..f081982689c6d195dc0fa4e829c22674c2854771 100644
--- a/core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
@@ -33,6 +33,11 @@ class ImageFieldDefaultImagesTest extends ImageFieldTestBase {
    */
   public static $modules = ['field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests CRUD for fields and field storages with default images.
    */
diff --git a/core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php b/core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php
index c7f5d8c6358b7d9875d1add5ff096729059e1fa5..c99256c9bcd2e5d6e28316f6f10a041bcad2c37e 100644
--- a/core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php
@@ -34,6 +34,11 @@ class ImageFieldDisplayTest extends ImageFieldTestBase {
    */
   public static $modules = ['field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Test image formatters on node display for public files.
    */
diff --git a/core/modules/image/tests/src/Functional/ImageFieldValidateTest.php b/core/modules/image/tests/src/Functional/ImageFieldValidateTest.php
index 1e531b23209ab2a02e38030c9d1f20221d0cfafd..59627521a5a19e3b04b3b2f018c55e5b3855c651 100644
--- a/core/modules/image/tests/src/Functional/ImageFieldValidateTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldValidateTest.php
@@ -17,6 +17,11 @@ class ImageFieldValidateTest extends ImageFieldTestBase {
     compareFiles as drupalCompareFiles;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test image validity.
    */
diff --git a/core/modules/image/tests/src/Functional/ImageFieldWidgetTest.php b/core/modules/image/tests/src/Functional/ImageFieldWidgetTest.php
index cdec5b905e736a0cf3c10de5dbb9fb2cee0d2c0a..655e7ab8a8926992034d6f7fbee45ed03bd04e01 100644
--- a/core/modules/image/tests/src/Functional/ImageFieldWidgetTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldWidgetTest.php
@@ -11,6 +11,11 @@
  */
 class ImageFieldWidgetTest extends ImageFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests file widget element.
    */
diff --git a/core/modules/image/tests/src/Functional/ImageOnTranslatedEntityTest.php b/core/modules/image/tests/src/Functional/ImageOnTranslatedEntityTest.php
index e4bde9261c9029dcd235a09464685c3b6ebbdad0..c0f01f2719ae31c630e1c9c54988b8b07f3a5211 100644
--- a/core/modules/image/tests/src/Functional/ImageOnTranslatedEntityTest.php
+++ b/core/modules/image/tests/src/Functional/ImageOnTranslatedEntityTest.php
@@ -22,6 +22,11 @@ class ImageOnTranslatedEntityTest extends ImageFieldTestBase {
    */
   public static $modules = ['language', 'content_translation', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the image field used in the test.
    *
diff --git a/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php b/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php
index fff27601ce23866ef721911e662fd7ff78e8c5bb..71554333b6c851f171c443d6b6df87c058229c70 100644
--- a/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php
+++ b/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php
@@ -12,6 +12,11 @@
  */
 class ImageStyleDeleteTest extends ImageFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/Functional/ImageStyleFlushTest.php b/core/modules/image/tests/src/Functional/ImageStyleFlushTest.php
index 17490119e2ee9a4186e3411f9b05808ac896cb93..a5036eec8f2cc51e781848203e82ff4303ce93c1 100644
--- a/core/modules/image/tests/src/Functional/ImageStyleFlushTest.php
+++ b/core/modules/image/tests/src/Functional/ImageStyleFlushTest.php
@@ -18,6 +18,11 @@ class ImageStyleFlushTest extends ImageFieldTestBase {
     compareFiles as drupalCompareFiles;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Given an image style and a wrapper, generate an image.
    */
diff --git a/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php b/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
index 381440fe0791ac27b5446f44536d7e6829a680b5..194f6e57a2b9b0af66a8b2fcba74adec72ce6b01 100644
--- a/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
+++ b/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
@@ -28,6 +28,11 @@ class ImageStylesPathAndUrlTest extends BrowserTestBase {
    */
   public static $modules = ['image', 'image_module_test', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The image style.
    *
diff --git a/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php b/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
index a037d4808d66d725c746c9896bc6802bea80b71d..ab95773a5964ae4acbec746484beeaa7b4c760f0 100644
--- a/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
+++ b/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
@@ -24,6 +24,11 @@ class QuickEditImageControllerTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'image', 'quickedit'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The machine name of our image field.
    *
diff --git a/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonAnonTest.php b/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonAnonTest.php
index e367fb6e672669e2c62cf82746fd59b153c10278..a6b62aa34682aaec15fec3d36c6c1a7f7b8c9c3e 100644
--- a/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonAnonTest.php
+++ b/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonAnonTest.php
@@ -21,4 +21,9 @@ class ImageStyleJsonAnonTest extends ImageStyleResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonBasicAuthTest.php b/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonBasicAuthTest.php
index ab6ae57d5323f065d236d87e8670e883bc6e9d92..5d4ba8648e9d215a8d57df312039bbccfd679161 100644
--- a/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonBasicAuthTest.php
+++ b/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ImageStyleJsonBasicAuthTest extends ImageStyleResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonCookieTest.php b/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonCookieTest.php
index 5021233662620dc79d7f7f367eb0ff04ac3b497b..0d0bb88e897b417c61b3c2b962fbcfa5ea7534e3 100644
--- a/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonCookieTest.php
+++ b/core/modules/image/tests/src/Functional/Rest/ImageStyleJsonCookieTest.php
@@ -26,4 +26,9 @@ class ImageStyleJsonCookieTest extends ImageStyleResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlAnonTest.php b/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlAnonTest.php
index 427641aa4b617b6289770691e7498f76a084cc44..8f976f308e8cd01da07e6149390bc07030a4926a 100644
--- a/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlAnonTest.php
+++ b/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlAnonTest.php
@@ -23,6 +23,11 @@ class ImageStyleXmlAnonTest extends ImageStyleResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlBasicAuthTest.php b/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlBasicAuthTest.php
index cd376a3140e6b3653487e5886471a1497c5d629c..052a50e97a432b789794f66e2385aa7d7f8ddff9 100644
--- a/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlBasicAuthTest.php
+++ b/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ImageStyleXmlBasicAuthTest extends ImageStyleResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlCookieTest.php b/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlCookieTest.php
index 7ca459a0ae08dae36814847795d588faef69bca3..75554393e31c52e37588ed3dbb5730ff22ab100d 100644
--- a/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlCookieTest.php
+++ b/core/modules/image/tests/src/Functional/Rest/ImageStyleXmlCookieTest.php
@@ -28,6 +28,11 @@ class ImageStyleXmlCookieTest extends ImageStyleResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/tests/src/FunctionalJavascript/ImageAdminStylesTest.php b/core/modules/image/tests/src/FunctionalJavascript/ImageAdminStylesTest.php
index e573c89a885e5e6000cc88be3d66b7cf8d21be58..67ad74c25dec02ec3b1bc5b74d0c19a643235579 100644
--- a/core/modules/image/tests/src/FunctionalJavascript/ImageAdminStylesTest.php
+++ b/core/modules/image/tests/src/FunctionalJavascript/ImageAdminStylesTest.php
@@ -11,6 +11,11 @@
  */
 class ImageAdminStylesTest extends ImageFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests editing Ajax-enabled image effect forms.
    */
diff --git a/core/modules/image/tests/src/FunctionalJavascript/ImageFieldValidateTest.php b/core/modules/image/tests/src/FunctionalJavascript/ImageFieldValidateTest.php
index 02ca72d19e762b44ab0d04551c1ca8e8efaee276..a8907d74c99173eb6244c7129bddc8da6eae313b 100644
--- a/core/modules/image/tests/src/FunctionalJavascript/ImageFieldValidateTest.php
+++ b/core/modules/image/tests/src/FunctionalJavascript/ImageFieldValidateTest.php
@@ -12,6 +12,11 @@
  */
 class ImageFieldValidateTest extends ImageFieldTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test the validation message is displayed only once for ajax uploads.
    */
diff --git a/core/modules/image/tests/src/FunctionalJavascript/QuickEditImageTest.php b/core/modules/image/tests/src/FunctionalJavascript/QuickEditImageTest.php
index b4444eff2b0972562fe9904e92b82c6a0651fbdd..2b1dd79dbf668195bd3f820847b63d9b3bc09d00 100644
--- a/core/modules/image/tests/src/FunctionalJavascript/QuickEditImageTest.php
+++ b/core/modules/image/tests/src/FunctionalJavascript/QuickEditImageTest.php
@@ -22,6 +22,11 @@ class QuickEditImageTest extends QuickEditJavascriptTestBase {
    */
   public static $modules = ['node', 'image', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permissions to edit Articles and use Quick Edit.
    *
diff --git a/core/modules/inline_form_errors/tests/src/Functional/FormErrorHandlerFileUploadTest.php b/core/modules/inline_form_errors/tests/src/Functional/FormErrorHandlerFileUploadTest.php
index 9535c99fb2005d55fa591f1ec7a442bdda4add2e..20f4e32132bb2d74af7426369697bee9118c6015 100644
--- a/core/modules/inline_form_errors/tests/src/Functional/FormErrorHandlerFileUploadTest.php
+++ b/core/modules/inline_form_errors/tests/src/Functional/FormErrorHandlerFileUploadTest.php
@@ -21,6 +21,11 @@ class FormErrorHandlerFileUploadTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'file', 'field_ui', 'inline_form_errors'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerCKEditorTest.php b/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerCKEditorTest.php
index 7c9a74ab503488f95d5255c3e308dc554ea255f3..a99c1b838792c6638341e2d2af52c4986ac1dcd3 100644
--- a/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerCKEditorTest.php
+++ b/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerCKEditorTest.php
@@ -22,6 +22,11 @@ class FormErrorHandlerCKEditorTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'ckeditor', 'inline_form_errors', 'filter'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerQuickEditTest.php b/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerQuickEditTest.php
index 00dc3d3f622360c2fdb181cef35ce018ea1bd6b4..4fcac0f097d358ab295cb50237592ad74b8d810a 100644
--- a/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerQuickEditTest.php
+++ b/core/modules/inline_form_errors/tests/src/FunctionalJavascript/FormErrorHandlerQuickEditTest.php
@@ -23,6 +23,11 @@ class FormErrorHandlerQuickEditTest extends WebDriverTestBase {
     'inline_form_errors',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * An editor user with permissions to access the in-place editor.
    *
diff --git a/core/modules/jsonapi/tests/src/Functional/ActionTest.php b/core/modules/jsonapi/tests/src/Functional/ActionTest.php
index 796494c21d209810ee241f3ee184b826d36be2b1..724e08455b5898a4f90adb9eedc0ef3da75f7ac6 100644
--- a/core/modules/jsonapi/tests/src/Functional/ActionTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ActionTest.php
@@ -35,6 +35,11 @@ class ActionTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/BaseFieldOverrideTest.php b/core/modules/jsonapi/tests/src/Functional/BaseFieldOverrideTest.php
index 98c56d0502ca925d6ad971829432778e82eba46a..39bdd150cf7bbb71fcc5d5a115b63294cb826235 100644
--- a/core/modules/jsonapi/tests/src/Functional/BaseFieldOverrideTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/BaseFieldOverrideTest.php
@@ -35,6 +35,11 @@ class BaseFieldOverrideTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/BlockContentTest.php b/core/modules/jsonapi/tests/src/Functional/BlockContentTest.php
index b06ffdc1be36760e0f58616503baa41db558b222..d5e51e7a8d9214d429590acc9e24984b87e492cd 100644
--- a/core/modules/jsonapi/tests/src/Functional/BlockContentTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/BlockContentTest.php
@@ -39,6 +39,11 @@ class BlockContentTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/BlockContentTypeTest.php b/core/modules/jsonapi/tests/src/Functional/BlockContentTypeTest.php
index 0abe7283d05337c062044e1d44721aca17a0a4d9..49268a986b935df1fadec513b3604a931fd8e9c8 100644
--- a/core/modules/jsonapi/tests/src/Functional/BlockContentTypeTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/BlockContentTypeTest.php
@@ -34,6 +34,11 @@ class BlockContentTypeTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/BlockTest.php b/core/modules/jsonapi/tests/src/Functional/BlockTest.php
index 3827b0701922e7da0a59d6df24e481688dbdd59e..848dfa49f2e9da53921fa77ed77691da21833d7d 100644
--- a/core/modules/jsonapi/tests/src/Functional/BlockTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/BlockTest.php
@@ -35,6 +35,11 @@ class BlockTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/CommentTest.php b/core/modules/jsonapi/tests/src/Functional/CommentTest.php
index d9fc52ae9f7530af3503959a6e591d30408dc95c..4fd1bb786e1e46c80aac3c42288ffab70e61fa81 100644
--- a/core/modules/jsonapi/tests/src/Functional/CommentTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/CommentTest.php
@@ -41,6 +41,11 @@ class CommentTest extends ResourceTestBase {
    */
   protected static $resourceTypeName = 'comment--comment';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/CommentTypeTest.php b/core/modules/jsonapi/tests/src/Functional/CommentTypeTest.php
index 26ce5bac86565e49d019c99f5fe8d9c2c94ce1b8..fd8c73a990186b9bfd9dec58e86b289450b5077f 100644
--- a/core/modules/jsonapi/tests/src/Functional/CommentTypeTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/CommentTypeTest.php
@@ -34,6 +34,11 @@ class CommentTypeTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ConfigTestTest.php b/core/modules/jsonapi/tests/src/Functional/ConfigTestTest.php
index e6d873d04fd02472a677610f78a88a2e2b8a5151..3c6c7bd530d8a7d2e633d332573acdc6c6ce03b3 100644
--- a/core/modules/jsonapi/tests/src/Functional/ConfigTestTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ConfigTestTest.php
@@ -34,6 +34,11 @@ class ConfigTestTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ConfigurableLanguageTest.php b/core/modules/jsonapi/tests/src/Functional/ConfigurableLanguageTest.php
index 3aa479745e85531d6959b50bacb0810fa64f6776..fd03d5334943f939853a4678ab184502ea6dc226 100644
--- a/core/modules/jsonapi/tests/src/Functional/ConfigurableLanguageTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ConfigurableLanguageTest.php
@@ -38,6 +38,11 @@ class ConfigurableLanguageTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ContactFormTest.php b/core/modules/jsonapi/tests/src/Functional/ContactFormTest.php
index 993cff56ef68fbf4768dada71d7327a0725fd73a..3153e1853c1f741a2132360677d01d7b78d91ccc 100644
--- a/core/modules/jsonapi/tests/src/Functional/ContactFormTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ContactFormTest.php
@@ -34,6 +34,11 @@ class ContactFormTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ContentLanguageSettingsTest.php b/core/modules/jsonapi/tests/src/Functional/ContentLanguageSettingsTest.php
index 9eb9da53fef28c710017500a7c332d3c5e5983e5..597bcbc794b422d73c33929c2fd845326045b7e9 100644
--- a/core/modules/jsonapi/tests/src/Functional/ContentLanguageSettingsTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ContentLanguageSettingsTest.php
@@ -37,6 +37,11 @@ class ContentLanguageSettingsTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/DateFormatTest.php b/core/modules/jsonapi/tests/src/Functional/DateFormatTest.php
index 5c1dd997c4b8d8586b834d187877e9fc0dea5b0c..18b388e9107cdb3a882afda6f833f831fab7c455 100644
--- a/core/modules/jsonapi/tests/src/Functional/DateFormatTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/DateFormatTest.php
@@ -39,6 +39,11 @@ class DateFormatTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EditorTest.php b/core/modules/jsonapi/tests/src/Functional/EditorTest.php
index d0ec76b84b8ccdc0ebc8939f5705db4e52cde3e5..9b3c3805297921f383fd047bac8ad66109ad5d1f 100644
--- a/core/modules/jsonapi/tests/src/Functional/EditorTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EditorTest.php
@@ -37,6 +37,11 @@ class EditorTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EntityFormDisplayTest.php b/core/modules/jsonapi/tests/src/Functional/EntityFormDisplayTest.php
index 73190d265555248192f1db97982c8d13a3cab81b..1f914fec0699e94b8d5d6012b279d69cbdb3afcc 100644
--- a/core/modules/jsonapi/tests/src/Functional/EntityFormDisplayTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EntityFormDisplayTest.php
@@ -35,6 +35,11 @@ class EntityFormDisplayTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EntityFormModeTest.php b/core/modules/jsonapi/tests/src/Functional/EntityFormModeTest.php
index 9a1c36d7532acab87c64253abb6c02034c1103e6..637c77ea8f9a04f3ebc918b1d01e5abe0c5a2049 100644
--- a/core/modules/jsonapi/tests/src/Functional/EntityFormModeTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EntityFormModeTest.php
@@ -36,6 +36,11 @@ class EntityFormModeTest extends ResourceTestBase {
    */
   protected $entity;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EntityTestMapFieldTest.php b/core/modules/jsonapi/tests/src/Functional/EntityTestMapFieldTest.php
index b78f96cd7846e08068b7d4cfa1180201b3bfc093..82cea77007b5d368a3e98186ea5748606edf8ec2 100644
--- a/core/modules/jsonapi/tests/src/Functional/EntityTestMapFieldTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EntityTestMapFieldTest.php
@@ -56,6 +56,11 @@ class EntityTestMapFieldTest extends ResourceTestBase {
     ],
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EntityTestTest.php b/core/modules/jsonapi/tests/src/Functional/EntityTestTest.php
index fd3bf6b3a35fcb774e2405913dc0d218c6587fdd..fd6836eab3dbf3cee87dec2d33e7397ef0cab3cd 100644
--- a/core/modules/jsonapi/tests/src/Functional/EntityTestTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EntityTestTest.php
@@ -23,6 +23,11 @@ class EntityTestTest extends ResourceTestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EntityViewDisplayTest.php b/core/modules/jsonapi/tests/src/Functional/EntityViewDisplayTest.php
index 1b154cc10ec141ebe8498ae3099f3867608c11aa..0026706d3f4e3bcf6fe24d59280b69256fdca30a 100644
--- a/core/modules/jsonapi/tests/src/Functional/EntityViewDisplayTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EntityViewDisplayTest.php
@@ -18,6 +18,11 @@ class EntityViewDisplayTest extends ResourceTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EntityViewModeTest.php b/core/modules/jsonapi/tests/src/Functional/EntityViewModeTest.php
index 991b35fc93396c535f37030cc0cbc9a1e8438917..839b1fae68ac4857eb1b6378f3bf1567e14192b0 100644
--- a/core/modules/jsonapi/tests/src/Functional/EntityViewModeTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EntityViewModeTest.php
@@ -19,6 +19,11 @@ class EntityViewModeTest extends ResourceTestBase {
    */
   public static $modules = ['user', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/EntryPointTest.php b/core/modules/jsonapi/tests/src/Functional/EntryPointTest.php
index 2934ba066673f9cb773ce72fbba87782354e7798..2ab8da8c080b093f06782f4521dee409d47f112b 100644
--- a/core/modules/jsonapi/tests/src/Functional/EntryPointTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/EntryPointTest.php
@@ -29,6 +29,11 @@ class EntryPointTest extends BrowserTestBase {
     'basic_auth',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test GETing the entry point.
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ExternalNormalizersTest.php b/core/modules/jsonapi/tests/src/Functional/ExternalNormalizersTest.php
index 8d7218b988f7e9f04e8d9a66be96cf6ef53039de..33f6aab0de9d5a7c5f6e0fd61678ca8f3a83d9ed 100644
--- a/core/modules/jsonapi/tests/src/Functional/ExternalNormalizersTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ExternalNormalizersTest.php
@@ -21,6 +21,11 @@
  */
 class ExternalNormalizersTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The original value for the test field.
    *
diff --git a/core/modules/jsonapi/tests/src/Functional/FeedTest.php b/core/modules/jsonapi/tests/src/Functional/FeedTest.php
index 5ca4f906f670c2e1a574c229080ce038d012f747..7944a95c604e6ab21ae701c59c5671f0f80b334f 100644
--- a/core/modules/jsonapi/tests/src/Functional/FeedTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/FeedTest.php
@@ -20,6 +20,11 @@ class FeedTest extends ResourceTestBase {
    */
   public static $modules = ['aggregator'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/FieldConfigTest.php b/core/modules/jsonapi/tests/src/Functional/FieldConfigTest.php
index 311c098e43ed19398d2913a41b3c39f8ecb6bbb8..25a3889f4573da1082666cd747523cf7a94f5552 100644
--- a/core/modules/jsonapi/tests/src/Functional/FieldConfigTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/FieldConfigTest.php
@@ -21,6 +21,11 @@ class FieldConfigTest extends ResourceTestBase {
    */
   public static $modules = ['field', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/FieldStorageConfigTest.php b/core/modules/jsonapi/tests/src/Functional/FieldStorageConfigTest.php
index 0f75906bbb0d7514b2e0852e70db5ec704e39ffa..6e03be1261540b8e048a51aacd9e401020de05b3 100644
--- a/core/modules/jsonapi/tests/src/Functional/FieldStorageConfigTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/FieldStorageConfigTest.php
@@ -17,6 +17,11 @@ class FieldStorageConfigTest extends ResourceTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/FileTest.php b/core/modules/jsonapi/tests/src/Functional/FileTest.php
index ff674174ed44e0362195b096f4b7dc09668f9dce..deaa5be8265659e226a08adc3c957733c53c4ec9 100644
--- a/core/modules/jsonapi/tests/src/Functional/FileTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/FileTest.php
@@ -26,6 +26,11 @@ class FileTest extends ResourceTestBase {
    */
   public static $modules = ['file', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php b/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php
index e57b8146999061e005d2ac52cbadc6106f186c89..3561ebae6559100d1c7e6cb89dd8716c2bf17a06 100644
--- a/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/FileUploadTest.php
@@ -27,6 +27,11 @@ class FileUploadTest extends ResourceTestBase {
    */
   public static $modules = ['entity_test', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/modules/jsonapi/tests/src/Functional/FilterFormatTest.php b/core/modules/jsonapi/tests/src/Functional/FilterFormatTest.php
index 8af68bb36377f0f35e70ddd21266a93753da4bea..c5b581d9ac7178d34bbed256dd5638ef43a516d9 100644
--- a/core/modules/jsonapi/tests/src/Functional/FilterFormatTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/FilterFormatTest.php
@@ -17,6 +17,11 @@ class FilterFormatTest extends ResourceTestBase {
    */
   public static $modules = ['filter'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ImageStyleTest.php b/core/modules/jsonapi/tests/src/Functional/ImageStyleTest.php
index 55193d81a5ac79437df0d931b950501c6ad3e37b..47ec1ace8ccb9f2161d2e206508d2911be54dbaf 100644
--- a/core/modules/jsonapi/tests/src/Functional/ImageStyleTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ImageStyleTest.php
@@ -17,6 +17,11 @@ class ImageStyleTest extends ResourceTestBase {
    */
   public static $modules = ['image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/InternalEntitiesTest.php b/core/modules/jsonapi/tests/src/Functional/InternalEntitiesTest.php
index e170222a086e3be78ab1ffbadf9ae51e7551ca33..a0550d15976c2182881621f79ec5b1b95deb98f0 100644
--- a/core/modules/jsonapi/tests/src/Functional/InternalEntitiesTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/InternalEntitiesTest.php
@@ -30,6 +30,11 @@ class InternalEntitiesTest extends BrowserTestBase {
     'serialization',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A test user.
    *
diff --git a/core/modules/jsonapi/tests/src/Functional/ItemTest.php b/core/modules/jsonapi/tests/src/Functional/ItemTest.php
index 6e3a48f027ab720431213f12c5dc0e498663827c..eae850acc2d36ec6aba76bad8a3972a2f00567b2 100644
--- a/core/modules/jsonapi/tests/src/Functional/ItemTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ItemTest.php
@@ -20,6 +20,11 @@ class ItemTest extends ResourceTestBase {
    */
   public static $modules = ['aggregator'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalMultilingualTest.php b/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalMultilingualTest.php
index 65cdf3c8baff0297705a2a93643e5dc3620433fa..4748d68bcc4ef6ae4cd3dd2bc7948c52ffc7a2f1 100644
--- a/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalMultilingualTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalMultilingualTest.php
@@ -28,6 +28,11 @@ class JsonApiFunctionalMultilingualTest extends JsonApiFunctionalTestBase {
     'content_translation',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php b/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php
index bae30d70040b8cb92039393bdbeeac052ed23733..3acde839e798689577845a59b23c8cfd7902c261 100644
--- a/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTest.php
@@ -23,6 +23,11 @@ class JsonApiFunctionalTest extends JsonApiFunctionalTestBase {
     'basic_auth',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test the GET method.
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTestBase.php b/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTestBase.php
index bca821d014f71ec1feceaf3b525a346e77e5ec19..f907ccfc4de91dce28d4253bd4b7497d1d06a7f7 100644
--- a/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTestBase.php
+++ b/core/modules/jsonapi/tests/src/Functional/JsonApiFunctionalTestBase.php
@@ -42,6 +42,11 @@ abstract class JsonApiFunctionalTestBase extends BrowserTestBase {
     'link',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test user.
    *
diff --git a/core/modules/jsonapi/tests/src/Functional/JsonApiRegressionTest.php b/core/modules/jsonapi/tests/src/Functional/JsonApiRegressionTest.php
index d8ba8bb94b014179f590bb81861c1ca34197c780..2aec3d96a56765c025817aa93232e445aaa31de8 100644
--- a/core/modules/jsonapi/tests/src/Functional/JsonApiRegressionTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/JsonApiRegressionTest.php
@@ -43,6 +43,11 @@ class JsonApiRegressionTest extends JsonApiFunctionalTestBase {
     'basic_auth',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensure filtering on relationships works with bundle-specific target types.
    *
diff --git a/core/modules/jsonapi/tests/src/Functional/MediaTest.php b/core/modules/jsonapi/tests/src/Functional/MediaTest.php
index ba7e63e662c6b543e5700027787ecd296811eacc..f604ca60924d1103660df28c4e1466f6d8409c4e 100644
--- a/core/modules/jsonapi/tests/src/Functional/MediaTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/MediaTest.php
@@ -24,6 +24,11 @@ class MediaTest extends ResourceTestBase {
    */
   public static $modules = ['media'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/MediaTypeTest.php b/core/modules/jsonapi/tests/src/Functional/MediaTypeTest.php
index 3e2a0151ec2a325b5ee2a9b28ba95b443b8edd41..8ae5e1bb78a53f1da2fc2932ca532a62b4312624 100644
--- a/core/modules/jsonapi/tests/src/Functional/MediaTypeTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/MediaTypeTest.php
@@ -17,6 +17,11 @@ class MediaTypeTest extends ResourceTestBase {
    */
   public static $modules = ['media'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/MenuLinkContentTest.php b/core/modules/jsonapi/tests/src/Functional/MenuLinkContentTest.php
index 41e68aede33cc54e76e5024373c91ba2b893b9db..847c49ff93d579ada017d090f8533f6fb5492dd2 100644
Binary files a/core/modules/jsonapi/tests/src/Functional/MenuLinkContentTest.php and b/core/modules/jsonapi/tests/src/Functional/MenuLinkContentTest.php differ
diff --git a/core/modules/jsonapi/tests/src/Functional/MenuTest.php b/core/modules/jsonapi/tests/src/Functional/MenuTest.php
index 2acb15f01a2622f6b329105be694b8953021dccb..6a6d9946a347e223bb23af2c38448ce689311c23 100644
--- a/core/modules/jsonapi/tests/src/Functional/MenuTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/MenuTest.php
@@ -17,6 +17,11 @@ class MenuTest extends ResourceTestBase {
    */
   public static $modules = [];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/MessageTest.php b/core/modules/jsonapi/tests/src/Functional/MessageTest.php
index 9b9ddf71a9f92061a9e6c7bff68be915f2d83dbd..5fcb72512bf9c7ce18a25a65f07b6de94bf04c6f 100644
--- a/core/modules/jsonapi/tests/src/Functional/MessageTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/MessageTest.php
@@ -21,6 +21,11 @@ class MessageTest extends ResourceTestBase {
    */
   public static $modules = ['contact'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/NodeTest.php b/core/modules/jsonapi/tests/src/Functional/NodeTest.php
index 3b3e830d791bebf2ae28ce7d2c7e70931c42a3f8..8493da6717af428c445f60e3e8ed2cc1c20b14ee 100644
--- a/core/modules/jsonapi/tests/src/Functional/NodeTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/NodeTest.php
@@ -28,6 +28,11 @@ class NodeTest extends ResourceTestBase {
    */
   public static $modules = ['node', 'path'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/NodeTypeTest.php b/core/modules/jsonapi/tests/src/Functional/NodeTypeTest.php
index eeeb4645ae194a082bedbee06abadf1b92b681ff..c7bc3e22230e90fc24788ad7270280542bb29e02 100644
--- a/core/modules/jsonapi/tests/src/Functional/NodeTypeTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/NodeTypeTest.php
@@ -17,6 +17,11 @@ class NodeTypeTest extends ResourceTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/PathAliasTest.php b/core/modules/jsonapi/tests/src/Functional/PathAliasTest.php
index 3b80c5f069564f8338f2c8fd43b528f3f4374db4..ce2e90465e7cf69deec3c4c51eaf13bad912b266 100644
--- a/core/modules/jsonapi/tests/src/Functional/PathAliasTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/PathAliasTest.php
@@ -18,6 +18,11 @@ class PathAliasTest extends ResourceTestBase {
    */
   public static $modules = ['user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/RdfMappingTest.php b/core/modules/jsonapi/tests/src/Functional/RdfMappingTest.php
index 2570e9756efff4a96b49adac3a7ff3b7a32bb870..0082d52a3f16d9265002bcb3fadb0840bb4e34f8 100644
--- a/core/modules/jsonapi/tests/src/Functional/RdfMappingTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/RdfMappingTest.php
@@ -18,6 +18,11 @@ class RdfMappingTest extends ResourceTestBase {
    */
   public static $modules = ['node', 'rdf'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ResponsiveImageStyleTest.php b/core/modules/jsonapi/tests/src/Functional/ResponsiveImageStyleTest.php
index 298dc48d0099f8f89954817f12a348e46ad49032..d70d4b75ec5342a389bccdaf641e48627a353f48 100644
--- a/core/modules/jsonapi/tests/src/Functional/ResponsiveImageStyleTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ResponsiveImageStyleTest.php
@@ -17,6 +17,11 @@ class ResponsiveImageStyleTest extends ResourceTestBase {
    */
   public static $modules = ['responsive_image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/RestExportJsonApiUnsupported.php b/core/modules/jsonapi/tests/src/Functional/RestExportJsonApiUnsupported.php
index 7efe1aa2e189f4cd32ea1330f0a9e6e69c328e84..eb38ccd01165407323ee4eee98b0ce91a9b645bf 100644
--- a/core/modules/jsonapi/tests/src/Functional/RestExportJsonApiUnsupported.php
+++ b/core/modules/jsonapi/tests/src/Functional/RestExportJsonApiUnsupported.php
@@ -24,6 +24,11 @@ class RestExportJsonApiUnsupported extends ViewTestBase {
    */
   public static $modules = ['jsonapi', 'rest_test_views', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/RestJsonApiUnsupported.php b/core/modules/jsonapi/tests/src/Functional/RestJsonApiUnsupported.php
index 8577caca29f4a62fdc4d4bcbba5cd02f3a7311f3..27cc2b221929f62e0af0b2b1369ee82aef790859 100644
--- a/core/modules/jsonapi/tests/src/Functional/RestJsonApiUnsupported.php
+++ b/core/modules/jsonapi/tests/src/Functional/RestJsonApiUnsupported.php
@@ -24,6 +24,11 @@ class RestJsonApiUnsupported extends ResourceTestBase {
    */
   public static $modules = ['jsonapi', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/RestResourceConfigTest.php b/core/modules/jsonapi/tests/src/Functional/RestResourceConfigTest.php
index f44ebd0decf48462891ebb5c651bbf2fa0358a6c..b1de33b048f7d99516657ca41565d9331d4d3bfc 100644
--- a/core/modules/jsonapi/tests/src/Functional/RestResourceConfigTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/RestResourceConfigTest.php
@@ -17,6 +17,11 @@ class RestResourceConfigTest extends ResourceTestBase {
    */
   public static $modules = ['rest', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/RoleTest.php b/core/modules/jsonapi/tests/src/Functional/RoleTest.php
index 4f8d609a220baba2723c2d4bb9fac0dd812a8fb3..c3ad6e4608debc4473e8a1804ff51ea355faecf9 100644
--- a/core/modules/jsonapi/tests/src/Functional/RoleTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/RoleTest.php
@@ -18,6 +18,11 @@ class RoleTest extends ResourceTestBase {
    */
   public static $modules = ['user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/SearchPageTest.php b/core/modules/jsonapi/tests/src/Functional/SearchPageTest.php
index 4f741d6335a14d0a48d82f5bbe6a204e2160f4bd..ebf9275f0b7c32ba9d6d140ec2db831f7b8c8c65 100644
--- a/core/modules/jsonapi/tests/src/Functional/SearchPageTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/SearchPageTest.php
@@ -17,6 +17,11 @@ class SearchPageTest extends ResourceTestBase {
    */
   public static $modules = ['node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ShortcutSetTest.php b/core/modules/jsonapi/tests/src/Functional/ShortcutSetTest.php
index 0ab41a38b05fff2eed33a0d590aa3e0421bd7550..a6bcce4ece2bb4abd98f9d47e022d6075c6f57dd 100644
--- a/core/modules/jsonapi/tests/src/Functional/ShortcutSetTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ShortcutSetTest.php
@@ -17,6 +17,11 @@ class ShortcutSetTest extends ResourceTestBase {
    */
   public static $modules = ['shortcut'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ShortcutTest.php b/core/modules/jsonapi/tests/src/Functional/ShortcutTest.php
index 1cbb9caeddf8b1ddf7729a6f5ccf0062922b9429..925bef47382f8a3c53d090b482be4ac8451136d6 100644
--- a/core/modules/jsonapi/tests/src/Functional/ShortcutTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ShortcutTest.php
@@ -25,6 +25,11 @@ class ShortcutTest extends ResourceTestBase {
    */
   public static $modules = ['comment', 'shortcut'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/TermTest.php b/core/modules/jsonapi/tests/src/Functional/TermTest.php
index 2aecdb5e0c085ac3df74f5e5ed4287a23cd4d21a..f5f20aeec2500470477864b1053000d7c1f4f786 100644
--- a/core/modules/jsonapi/tests/src/Functional/TermTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/TermTest.php
@@ -26,6 +26,11 @@ class TermTest extends ResourceTestBase {
    */
   public static $modules = ['taxonomy', 'path'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/TestCoverageTest.php b/core/modules/jsonapi/tests/src/Functional/TestCoverageTest.php
index b3a2c6083b809daa89297c45e62bef7cbdd69540..92de8b451f705fb413516f1de6a7b2a02209e5f3 100644
--- a/core/modules/jsonapi/tests/src/Functional/TestCoverageTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/TestCoverageTest.php
@@ -19,6 +19,11 @@ class TestCoverageTest extends BrowserTestBase {
    */
   protected $definitions;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/TourTest.php b/core/modules/jsonapi/tests/src/Functional/TourTest.php
index e6d3488778e0b22818123c459260f233ca5b3025..80b1ea8c3cddf04f81b6894fd092df4893eba31d 100644
--- a/core/modules/jsonapi/tests/src/Functional/TourTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/TourTest.php
@@ -17,6 +17,11 @@ class TourTest extends ResourceTestBase {
    */
   public static $modules = ['tour'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/UserTest.php b/core/modules/jsonapi/tests/src/Functional/UserTest.php
index e9aa7b6bf319c6300f502ada5cb96114f944ed27..f4ce93f2aa912e3f682bad159cc824c33f5e34ec 100644
--- a/core/modules/jsonapi/tests/src/Functional/UserTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/UserTest.php
@@ -24,6 +24,11 @@ class UserTest extends ResourceTestBase {
    */
   public static $modules = ['user', 'jsonapi_test_user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/ViewTest.php b/core/modules/jsonapi/tests/src/Functional/ViewTest.php
index 236e8326ee369939ce9bcd81af72bbe6289b96f8..3817541f1fc65f7987fc7a991680505493a7fb57 100644
--- a/core/modules/jsonapi/tests/src/Functional/ViewTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/ViewTest.php
@@ -17,6 +17,11 @@ class ViewTest extends ResourceTestBase {
    */
   public static $modules = ['views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/VocabularyTest.php b/core/modules/jsonapi/tests/src/Functional/VocabularyTest.php
index 61ecdc811a6dd31e71794cfd9194ffcbc1569743..a3e2a066cf7c7f53b1b870fe238996e87fdc0d9d 100644
--- a/core/modules/jsonapi/tests/src/Functional/VocabularyTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/VocabularyTest.php
@@ -17,6 +17,11 @@ class VocabularyTest extends ResourceTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/jsonapi/tests/src/Functional/WorkflowTest.php b/core/modules/jsonapi/tests/src/Functional/WorkflowTest.php
index 6ad93d50f7721ea9670600dc4b16b36758bc43bf..50ffd46fb17a33c876c180cfca883b598113a54f 100644
--- a/core/modules/jsonapi/tests/src/Functional/WorkflowTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/WorkflowTest.php
@@ -17,6 +17,11 @@ class WorkflowTest extends ResourceTestBase {
    */
   public static $modules = ['workflows', 'workflow_type_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/AdminPathEntityConverterLanguageTest.php b/core/modules/language/tests/src/Functional/AdminPathEntityConverterLanguageTest.php
index f689a9233fee9e6b36c52e896fa8e6ade99d1d8a..a9ea8cc8ce7d46a7d1bb548dd94b6419b68c9eee 100644
--- a/core/modules/language/tests/src/Functional/AdminPathEntityConverterLanguageTest.php
+++ b/core/modules/language/tests/src/Functional/AdminPathEntityConverterLanguageTest.php
@@ -14,6 +14,11 @@ class AdminPathEntityConverterLanguageTest extends BrowserTestBase {
 
   public static $modules = ['language', 'language_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $permissions = [
diff --git a/core/modules/language/tests/src/Functional/ConfigurableLanguageManagerTest.php b/core/modules/language/tests/src/Functional/ConfigurableLanguageManagerTest.php
index f1732920c4f8f335e94bfb8d599ec4fa105b89a3..49d9c0823e100ed5f07472bd6a42e22d34158c7a 100644
--- a/core/modules/language/tests/src/Functional/ConfigurableLanguageManagerTest.php
+++ b/core/modules/language/tests/src/Functional/ConfigurableLanguageManagerTest.php
@@ -34,6 +34,11 @@ class ConfigurableLanguageManagerTest extends BrowserTestBase {
     'user',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/EntityTypeWithoutLanguageFormTest.php b/core/modules/language/tests/src/Functional/EntityTypeWithoutLanguageFormTest.php
index f7b6191484dba4753000f1226423fbc7369d3b0a..b5d85afd24fc4623cbf69f6d373e20b03fa50dd2 100644
--- a/core/modules/language/tests/src/Functional/EntityTypeWithoutLanguageFormTest.php
+++ b/core/modules/language/tests/src/Functional/EntityTypeWithoutLanguageFormTest.php
@@ -24,6 +24,11 @@ class EntityTypeWithoutLanguageFormTest extends BrowserTestBase {
     'language_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonAnonTest.php b/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonAnonTest.php
index c548c17241d53047d5c0d1e5234535d1f6af89dc..f2759d93f8fb680c3d2b51d4a83eb444a4135d27 100644
--- a/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonAnonTest.php
+++ b/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ConfigurableLanguageHalJsonAnonTest extends ConfigurableLanguageResourceTe
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonBasicAuthTest.php b/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonBasicAuthTest.php
index 4647acb82a08bbe473899b300847e7f3a16ff2d0..f0803aa55390f1d8fb7ec9d6eb50ff6b95a6e120 100644
--- a/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonBasicAuthTest.php
+++ b/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class ConfigurableLanguageHalJsonBasicAuthTest extends ConfigurableLanguageResou
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonCookieTest.php b/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonCookieTest.php
index 9ad756106743b54d952e86bedac30f7940a25bf1..68fe2bf4524d499bace8fa86d1e8e1de10f53751 100644
--- a/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonCookieTest.php
+++ b/core/modules/language/tests/src/Functional/Hal/ConfigurableLanguageHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ConfigurableLanguageHalJsonCookieTest extends ConfigurableLanguageResource
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonAnonTest.php b/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonAnonTest.php
index d5b7947ed47e4f15f82697b8c0e042573a605790..88bf96eb1d204de3f8995d4d49766243bc545290 100644
--- a/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonAnonTest.php
+++ b/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ContentLanguageSettingsHalJsonAnonTest extends ContentLanguageSettingsReso
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonBasicAuthTest.php b/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonBasicAuthTest.php
index fefd0db73a7ad75f96cc4a5bcfd944cf26d067ff..ec6f172a597f609489da3ef45ca1586a8309f5ed 100644
--- a/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonBasicAuthTest.php
+++ b/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class ContentLanguageSettingsHalJsonBasicAuthTest extends ContentLanguageSetting
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonCookieTest.php b/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonCookieTest.php
index 63584f6489773c4d57a94a9c9525ec2cb156ddbf..e9ed29cf3549243d15f0a71b0cbdb812af1418da 100644
--- a/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonCookieTest.php
+++ b/core/modules/language/tests/src/Functional/Hal/ContentLanguageSettingsHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ContentLanguageSettingsHalJsonCookieTest extends ContentLanguageSettingsRe
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageBlockSettingsVisibilityTest.php b/core/modules/language/tests/src/Functional/LanguageBlockSettingsVisibilityTest.php
index 003c5a63fa60b5eeedb040ed4845231e58033ff1..1511bf1f14915173f9f776316df5a37f63be7ed9 100644
--- a/core/modules/language/tests/src/Functional/LanguageBlockSettingsVisibilityTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageBlockSettingsVisibilityTest.php
@@ -13,6 +13,11 @@ class LanguageBlockSettingsVisibilityTest extends BrowserTestBase {
 
   public static $modules = ['block', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testUnnecessaryLanguageSettingsVisibility() {
     $admin_user = $this->drupalCreateUser(['administer languages', 'access administration pages', 'administer blocks']);
     $this->drupalLogin($admin_user);
diff --git a/core/modules/language/tests/src/Functional/LanguageBreadcrumbTest.php b/core/modules/language/tests/src/Functional/LanguageBreadcrumbTest.php
index e15fcf7a6d67d61029b9e7b03b76749649680c8a..964da0d04b4160eeecccd6cbf8795066ab6a1ed3 100644
--- a/core/modules/language/tests/src/Functional/LanguageBreadcrumbTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageBreadcrumbTest.php
@@ -19,6 +19,11 @@ class LanguageBreadcrumbTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'block', 'filter'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageBrowserDetectionAcceptLanguageTest.php b/core/modules/language/tests/src/Functional/LanguageBrowserDetectionAcceptLanguageTest.php
index 1d1ea9c59956ad398d059ad9b0f741685a339365..849d59f9743545bfc863eaf7d5573e0a0b828639 100644
--- a/core/modules/language/tests/src/Functional/LanguageBrowserDetectionAcceptLanguageTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageBrowserDetectionAcceptLanguageTest.php
@@ -19,6 +19,11 @@ class LanguageBrowserDetectionAcceptLanguageTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'locale', 'content_translation', 'system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageBrowserDetectionTest.php b/core/modules/language/tests/src/Functional/LanguageBrowserDetectionTest.php
index b0b383bdf8cf255077d731ed54c61342c4c0f2bb..6c76a021112e54befa268bc1145e0db76535657a 100644
--- a/core/modules/language/tests/src/Functional/LanguageBrowserDetectionTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageBrowserDetectionTest.php
@@ -14,6 +14,11 @@ class LanguageBrowserDetectionTest extends BrowserTestBase {
 
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests for adding, editing and deleting mappings between browser language
    * codes and Drupal language codes.
diff --git a/core/modules/language/tests/src/Functional/LanguageConfigOverrideImportTest.php b/core/modules/language/tests/src/Functional/LanguageConfigOverrideImportTest.php
index 2ddd4963ed3e10c109f5cde596bd4c334e27c40e..03f3df28b51870af14d8a36a5a7f93f73460961e 100644
--- a/core/modules/language/tests/src/Functional/LanguageConfigOverrideImportTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigOverrideImportTest.php
@@ -19,6 +19,11 @@ class LanguageConfigOverrideImportTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'config', 'locale', 'config_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that language can be enabled and overrides are created during a sync.
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageConfigSchemaTest.php b/core/modules/language/tests/src/Functional/LanguageConfigSchemaTest.php
index e19fe53da32e5d6b0e60118bf93cd39670e03803..b2e384161b62c7ade834d29687f35dc9d9eedf19 100644
--- a/core/modules/language/tests/src/Functional/LanguageConfigSchemaTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigSchemaTest.php
@@ -21,6 +21,11 @@ class LanguageConfigSchemaTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'menu_link_content'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administrative permissions.
    *
diff --git a/core/modules/language/tests/src/Functional/LanguageConfigurationElementTest.php b/core/modules/language/tests/src/Functional/LanguageConfigurationElementTest.php
index 7d400cab4cbaf344287ff8512c7d069393c8fd61..5c5640abb4899a3a296ca7f38ff51d8c22613ad5 100644
--- a/core/modules/language/tests/src/Functional/LanguageConfigurationElementTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigurationElementTest.php
@@ -22,6 +22,11 @@ class LanguageConfigurationElementTest extends BrowserTestBase {
    */
   public static $modules = ['taxonomy', 'node', 'language', 'language_elements_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $user = $this->drupalCreateUser(['access administration pages', 'administer languages', 'administer content types']);
diff --git a/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
index 777ff110e82438fb3ae0dc50b7d03133a014a575..06f4cee3ba7111314b43ce064bf2ac5e0fec3513 100644
--- a/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
@@ -22,6 +22,11 @@ class LanguageConfigurationTest extends BrowserTestBase {
    */
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Functional tests for adding, editing and deleting languages.
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageCustomLanguageConfigurationTest.php b/core/modules/language/tests/src/Functional/LanguageCustomLanguageConfigurationTest.php
index ab3148dac362e158496ea977f3dbfa2719bd0ef4..52bbde11725ca10f793e9e40058ed40dc8cec7a2 100644
--- a/core/modules/language/tests/src/Functional/LanguageCustomLanguageConfigurationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageCustomLanguageConfigurationTest.php
@@ -21,6 +21,11 @@ class LanguageCustomLanguageConfigurationTest extends BrowserTestBase {
    */
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Functional tests for adding, editing and deleting languages.
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageEntityFieldAccessHookTest.php b/core/modules/language/tests/src/Functional/LanguageEntityFieldAccessHookTest.php
index 19b3217759bb21214eec7bfa519acdb8eb9f7edc..fac20719d11825035e2e0924a8512aff3e340dc2 100644
--- a/core/modules/language/tests/src/Functional/LanguageEntityFieldAccessHookTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageEntityFieldAccessHookTest.php
@@ -25,6 +25,11 @@ class LanguageEntityFieldAccessHookTest extends BrowserTestBase {
     'language_entity_field_access_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests compatibility with hook_entity_field_access().
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageListModuleInstallTest.php b/core/modules/language/tests/src/Functional/LanguageListModuleInstallTest.php
index 013d00d8dbe57d90deebdda20bf296e5535447dd..e63c31726c393b9c9a2943838e6fadd8387ee98d 100644
--- a/core/modules/language/tests/src/Functional/LanguageListModuleInstallTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageListModuleInstallTest.php
@@ -19,6 +19,11 @@ class LanguageListModuleInstallTest extends BrowserTestBase {
    */
   public static $modules = ['language_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests enabling Language.
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageListTest.php b/core/modules/language/tests/src/Functional/LanguageListTest.php
index 565ae586b343424a96e1cd3b99cd648f37cd4f7a..45ec251ba2461728d6499dfbe8da2bf7d816a27b 100644
--- a/core/modules/language/tests/src/Functional/LanguageListTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageListTest.php
@@ -22,6 +22,11 @@ class LanguageListTest extends BrowserTestBase {
    */
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Functional tests for adding, editing and deleting languages.
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageLocaleListTest.php b/core/modules/language/tests/src/Functional/LanguageLocaleListTest.php
index 844a8af13b5aafcea9a1e3b44b63f111198c9e58..2809d329862ea4b485cd96be522965288324533a 100644
--- a/core/modules/language/tests/src/Functional/LanguageLocaleListTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageLocaleListTest.php
@@ -19,6 +19,11 @@ class LanguageLocaleListTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php b/core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php
index b158078e7a0262f6033146cb1cdc02fba86b295e..66ea59ac1eeec929537fd1d15230cb1345bb41d2 100644
--- a/core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php
@@ -27,6 +27,11 @@ class LanguageNegotiationContentEntityTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'language_test', 'entity_test', 'system'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The entity being used for testing.
    *
diff --git a/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
index 374f748e1e3ee0136ecaf16314418498982c1756..bab82fd8fd6b7800a940243f262f0f8b96267f6b 100644
--- a/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
@@ -21,6 +21,11 @@ class LanguageNegotiationInfoTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageNegotiationUrlTest.php b/core/modules/language/tests/src/Functional/LanguageNegotiationUrlTest.php
index 07ae85d4338fb32e3e0129671f0fe190a026e132..673d08aeb4e595e20e8662582a8a6c17d90601d3 100644
--- a/core/modules/language/tests/src/Functional/LanguageNegotiationUrlTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageNegotiationUrlTest.php
@@ -22,6 +22,11 @@ class LanguageNegotiationUrlTest extends BrowserTestBase {
     'path',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @var \Drupal\user\Entity\User
    */
diff --git a/core/modules/language/tests/src/Functional/LanguagePathMonolingualTest.php b/core/modules/language/tests/src/Functional/LanguagePathMonolingualTest.php
index 17ff3f936df785d47882c1175c444ba1676a5112..5c4bcfa016078e46e5a0bc89b32ab5eaa45a2a72 100644
--- a/core/modules/language/tests/src/Functional/LanguagePathMonolingualTest.php
+++ b/core/modules/language/tests/src/Functional/LanguagePathMonolingualTest.php
@@ -18,6 +18,11 @@ class LanguagePathMonolingualTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'language', 'path'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/language/tests/src/Functional/LanguageSelectorTranslatableTest.php b/core/modules/language/tests/src/Functional/LanguageSelectorTranslatableTest.php
index 9526d226fdd7803fd4f75fe618353dd47e729df7..67695108517d2e4cf3856754a7cea1d710c00c44 100644
--- a/core/modules/language/tests/src/Functional/LanguageSelectorTranslatableTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageSelectorTranslatableTest.php
@@ -26,6 +26,11 @@ class LanguageSelectorTranslatableTest extends BrowserTestBase {
     'locale',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The user with administrator privileges.
    *
diff --git a/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php b/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
index 1303082c154d1aabeb17ddab740dbda3dc9e9d4f..6605a0c7de436282cf0104ddc90c05e2305e2231 100644
--- a/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
@@ -22,6 +22,11 @@ class LanguageSwitchingTest extends BrowserTestBase {
    */
   public static $modules = ['locale', 'locale_test', 'language', 'block', 'language_test', 'menu_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/language/tests/src/Functional/LanguageTourTest.php b/core/modules/language/tests/src/Functional/LanguageTourTest.php
index 13b29f2ef56fcd03ae2b985e56c9536840d3c4c9..9bae57720a6cb75a27e8fb53ab85ae9161312116 100644
--- a/core/modules/language/tests/src/Functional/LanguageTourTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageTourTest.php
@@ -25,6 +25,11 @@ class LanguageTourTest extends TourTestBase {
    */
   public static $modules = ['block', 'language', 'tour'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php b/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
index 57a6ab66ba268d6c61fb881ea398bcfabea65c26..ebf6366a577ae61e2e27b7d56aec022f84ae033c 100644
--- a/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
@@ -60,6 +60,11 @@ class LanguageUILanguageNegotiationTest extends BrowserTestBase {
    */
   public static $modules = ['locale', 'language_test', 'block', 'user', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php b/core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php
index 94f6fc6b90e398bed6a045a1fecac05e446c3ad7..49007619dfc1a87c30b1f421a72b3711b5f4dec2 100644
--- a/core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php
@@ -23,6 +23,11 @@ class LanguageUrlRewritingTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'language_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An user with permissions to administer languages.
    *
diff --git a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonAnonTest.php b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonAnonTest.php
index 7533e31c0e849280d30128cf7ac53a1765b3f066..572f2a9512cf06e2892d30d47637d14a7b415208 100644
--- a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonAnonTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonAnonTest.php
@@ -21,4 +21,9 @@ class ConfigurableLanguageJsonAnonTest extends ConfigurableLanguageResourceTestB
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonBasicAuthTest.php b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonBasicAuthTest.php
index 5352c9a951198a68630b786b2309da2e7952b946..e61892a299bffce3f31b9c4a32f533c1f3739225 100644
--- a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonBasicAuthTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ConfigurableLanguageJsonBasicAuthTest extends ConfigurableLanguageResource
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonCookieTest.php b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonCookieTest.php
index cd3d9ce73c34f40fdbd2b5226818e79573e9af46..a1b348b4413abd61b11d5b3b50729cbe7331636d 100644
--- a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonCookieTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageJsonCookieTest.php
@@ -26,4 +26,9 @@ class ConfigurableLanguageJsonCookieTest extends ConfigurableLanguageResourceTes
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlAnonTest.php b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlAnonTest.php
index 882b7bf458f577f2f57e319a3818becc6f7feac5..c787cd343c7bb7565794e9fd6970d74aa6ee58c6 100644
--- a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlAnonTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlAnonTest.php
@@ -23,4 +23,9 @@ class ConfigurableLanguageXmlAnonTest extends ConfigurableLanguageResourceTestBa
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlBasicAuthTest.php b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlBasicAuthTest.php
index afc017f7a019d39664db2fe1f6f9478bb8f17b77..7aff2d00fbb3e238800172e51e34cad6523a2339 100644
--- a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlBasicAuthTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ConfigurableLanguageXmlBasicAuthTest extends ConfigurableLanguageResourceT
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlCookieTest.php b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlCookieTest.php
index 7755d76e919b8d2a0d71001dd56d03851bc6379c..0d874619359fe3eb573c4ac386adc48b32d45b34 100644
--- a/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlCookieTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ConfigurableLanguageXmlCookieTest.php
@@ -28,4 +28,9 @@ class ConfigurableLanguageXmlCookieTest extends ConfigurableLanguageResourceTest
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonAnonTest.php b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonAnonTest.php
index 1bece31007cd8a70d19413e268d0644c86a98070..74de3ea30d118967a7518f1738d13b43399b1650 100644
--- a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonAnonTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonAnonTest.php
@@ -21,4 +21,9 @@ class ContentLanguageSettingsJsonAnonTest extends ContentLanguageSettingsResourc
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonBasicAuthTest.php b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonBasicAuthTest.php
index f1063a3dc11fb57dba1362d34a8159936e99e3e4..d68559fcd009a205f604a15604b199a61deeeedc 100644
--- a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonBasicAuthTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ContentLanguageSettingsJsonBasicAuthTest extends ContentLanguageSettingsRe
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonCookieTest.php b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonCookieTest.php
index 84da80849c4a6d0eba5c9554a352b3c1b0745332..9d38614cacf8008925b0fd7b8483141171d95d20 100644
--- a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonCookieTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsJsonCookieTest.php
@@ -26,4 +26,9 @@ class ContentLanguageSettingsJsonCookieTest extends ContentLanguageSettingsResou
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlAnonTest.php b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlAnonTest.php
index fd6519387e8bf14c893b7011c1a2a187a8447e99..102e85df52c300d5705e3fad2f6922a3f6cd45a3 100644
--- a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlAnonTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlAnonTest.php
@@ -23,4 +23,9 @@ class ContentLanguageSettingsXmlAnonTest extends ContentLanguageSettingsResource
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlBasicAuthTest.php b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlBasicAuthTest.php
index dee7ad27d4c92eb2fffcc46ec8a69f0427dbdf4d..1d1fad462c91741075e41655577e932de5802410 100644
--- a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlBasicAuthTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ContentLanguageSettingsXmlBasicAuthTest extends ContentLanguageSettingsRes
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlCookieTest.php b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlCookieTest.php
index a5b49684f7d6b62dd4be0b85df9959c12e0e9a6d..1c7ede1bf9f5b09b67f6766dce95e9cd236ee424 100644
--- a/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlCookieTest.php
+++ b/core/modules/language/tests/src/Functional/Rest/ContentLanguageSettingsXmlCookieTest.php
@@ -28,4 +28,9 @@ class ContentLanguageSettingsXmlCookieTest extends ContentLanguageSettingsResour
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonAnonTest.php b/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonAnonTest.php
index 1740380108daf9e8f8c778805d2249983ec02173..73da4c9b11f010e742b0bd24126a4de708a68d29 100644
--- a/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonAnonTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonAnonTest.php
@@ -28,4 +28,9 @@ class LayoutBuilderEntityViewDisplayHalJsonAnonTest extends LayoutBuilderEntityV
    */
   protected static $mimeType = 'application/hal+json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonCookieTest.php b/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonCookieTest.php
index bbc17736b7e748aa3d8b6552d19b602b182a9dab..ad272d297e6aa831255cfd3933360fd4e98b6fe5 100644
--- a/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonCookieTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Hal/LayoutBuilderEntityViewDisplayHalJsonCookieTest.php
@@ -17,4 +17,9 @@ class LayoutBuilderEntityViewDisplayHalJsonCookieTest extends LayoutBuilderEntit
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/layout_builder/tests/src/Functional/Jsonapi/LayoutBuilderEntityViewDisplayTest.php b/core/modules/layout_builder/tests/src/Functional/Jsonapi/LayoutBuilderEntityViewDisplayTest.php
index f6b76376eb1814c02f531171b5ee812ddc225ad4..628a014483fb9ccce7a4df22882ae9f768de93b3 100644
--- a/core/modules/layout_builder/tests/src/Functional/Jsonapi/LayoutBuilderEntityViewDisplayTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Jsonapi/LayoutBuilderEntityViewDisplayTest.php
@@ -18,6 +18,11 @@ class LayoutBuilderEntityViewDisplayTest extends EntityViewDisplayTest {
    */
   public static $modules = ['layout_builder'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderAccessTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderAccessTest.php
index af503f4ca155609175ace1c8a0bd67e268020779..55c69ac176ebf939b00575eceb94f238ab70de6f 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderAccessTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderAccessTest.php
@@ -22,6 +22,11 @@ class LayoutBuilderAccessTest extends BrowserTestBase {
     'user',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderFieldBlockThemeSuggestionsTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderFieldBlockThemeSuggestionsTest.php
index 4d47586dff63448c32510c911d9f155c419cbab0..9e465fc0c4c4e04acdebe360871f415cc3148d14 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderFieldBlockThemeSuggestionsTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderFieldBlockThemeSuggestionsTest.php
@@ -20,6 +20,11 @@ class LayoutBuilderFieldBlockThemeSuggestionsTest extends BrowserTestBase {
     'layout_builder_field_block_theme_suggestions_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderQuickEditTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderQuickEditTest.php
index e58f2c613fc6c9ec80f747ea03f9d791d6edff3a..6d786d2b14e387abcf30dfdc000fddc585aae172 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderQuickEditTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderQuickEditTest.php
@@ -20,6 +20,11 @@ class LayoutBuilderQuickEditTest extends BrowserTestBase {
     'quickedit',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderSectionStorageTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderSectionStorageTest.php
index 917322893918cbfca2dbc6a0ec9c606b6893cf3c..828bde2c1e33850f43aed07722bdcbb473e1b7c7 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderSectionStorageTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderSectionStorageTest.php
@@ -20,6 +20,11 @@ class LayoutBuilderSectionStorageTest extends BrowserTestBase {
     'layout_builder_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php
index c5efc3110df3c0c9c10c73046ecd3340334fcc0a..daf54a4f789c60d0e7074067593b54a108c3e3bc 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php
@@ -29,6 +29,11 @@ class LayoutBuilderTest extends BrowserTestBase {
     'layout_builder_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTranslationTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTranslationTest.php
index a86388277e333ec66ec7fdfd316781ae48bffe2f..0a0d5bedcd89e5ff1a1bd2897b8e076ac9dd6f37 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTranslationTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutBuilderTranslationTest.php
@@ -24,6 +24,11 @@ class LayoutBuilderTranslationTest extends ContentTranslationTestBase {
     'block',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The entity used for testing.
    *
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutDisplayTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutDisplayTest.php
index d1c4ba0ff6ac4f1d6fdcf36e99d4f38ae07f963f..a697b61e1d39327ab041897b81a0aa778e76988a 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutDisplayTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutDisplayTest.php
@@ -16,6 +16,11 @@ class LayoutDisplayTest extends BrowserTestBase {
    */
   protected static $modules = ['field_ui', 'layout_builder', 'block', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/LayoutSectionTest.php b/core/modules/layout_builder/tests/src/Functional/LayoutSectionTest.php
index 86ae521b1044fad48264cf7ce787ce289aa7fd93..dc7956238d533b4ca0f25bc85732543cd5056923 100644
--- a/core/modules/layout_builder/tests/src/Functional/LayoutSectionTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/LayoutSectionTest.php
@@ -20,6 +20,11 @@ class LayoutSectionTest extends BrowserTestBase {
    */
   public static $modules = ['field_ui', 'layout_builder', 'node', 'block_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonAnonTest.php b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonAnonTest.php
index 61fa91eff913ad3b6f70d469d5ec8cf74d3396e5..316c1f89161598b2e45df64125f5867e6755a04b 100644
--- a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonAnonTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonAnonTest.php
@@ -22,4 +22,9 @@ class LayoutBuilderEntityViewDisplayJsonAnonTest extends LayoutBuilderEntityView
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonBasicAuthTest.php b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonBasicAuthTest.php
index d92138f984639651f2700fad8f989b5d0f8e4e91..74fba46e5b210cccd63cf0acdeccd887e3a176b7 100644
--- a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonBasicAuthTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class LayoutBuilderEntityViewDisplayJsonBasicAuthTest extends LayoutBuilderEntit
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonCookieTest.php b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonCookieTest.php
index c96e7641b27eba001cc3b163b338931cfd7c8335..de311a73257e3f2b494cca84c391018589c65c60 100644
--- a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonCookieTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayJsonCookieTest.php
@@ -27,4 +27,9 @@ class LayoutBuilderEntityViewDisplayJsonCookieTest extends LayoutBuilderEntityVi
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlAnonTest.php b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlAnonTest.php
index 8c337c6552d5ec3a9bd7709fdbc37c47b7d8575c..63d3ba06634d5f35649bab01e38f8da6e3517ee7 100644
--- a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlAnonTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlAnonTest.php
@@ -24,4 +24,9 @@ class LayoutBuilderEntityViewDisplayXmlAnonTest extends LayoutBuilderEntityViewD
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlBasicAuthTest.php b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlBasicAuthTest.php
index 6ec5880699fe13f4c6ceaa5e3b164006eaa62834..6b9b9e35d798fa5b35ef7ce208d34772392e4278 100644
--- a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlBasicAuthTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlBasicAuthTest.php
@@ -19,6 +19,11 @@ class LayoutBuilderEntityViewDisplayXmlBasicAuthTest extends LayoutBuilderEntity
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlCookieTest.php b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlCookieTest.php
index 92925eca90ea8b394e4ff320c9389f2a7faa50c5..fef266ca49a2d8e6eecc37a04bde134c5a6a6a25 100644
--- a/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlCookieTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Rest/LayoutBuilderEntityViewDisplayXmlCookieTest.php
@@ -29,4 +29,9 @@ class LayoutBuilderEntityViewDisplayXmlCookieTest extends LayoutBuilderEntityVie
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/layout_builder/tests/src/Functional/Rest/OverrideSectionsTest.php b/core/modules/layout_builder/tests/src/Functional/Rest/OverrideSectionsTest.php
index 6d01a6803ce89c9d1a3b142dc3172a49aa19d29a..8549cfcbe09a877aa26d2889e69d92e555dc1163 100644
--- a/core/modules/layout_builder/tests/src/Functional/Rest/OverrideSectionsTest.php
+++ b/core/modules/layout_builder/tests/src/Functional/Rest/OverrideSectionsTest.php
@@ -20,6 +20,11 @@ class OverrideSectionsTest extends LayoutRestTestBase {
    */
   protected static $resourceConfigId = 'entity.node';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/AjaxBlockTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/AjaxBlockTest.php
index 9cedac930e5f1c19f27e104b1efd525aa161351a..99580cdef72b5eaeb5bb013f3df02c3c00fc5ea4 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/AjaxBlockTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/AjaxBlockTest.php
@@ -23,6 +23,11 @@ class AjaxBlockTest extends WebDriverTestBase {
     'layout_builder_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFilterTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFilterTest.php
index 86912bf58e9f92075fc673a11f628d360fd4b361..14e521cc99b729f65183ed08ec3ceafe9c8f5d16 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFilterTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFilterTest.php
@@ -23,6 +23,11 @@ class BlockFilterTest extends WebDriverTestBase {
     'user',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFormMessagesTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFormMessagesTest.php
index 8a86fa3ecc7eefe9c1036d37ed170363a7cf7584..39c366ed811a648782078c16d2d646c5e724ae07 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFormMessagesTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/BlockFormMessagesTest.php
@@ -26,6 +26,11 @@ class BlockFormMessagesTest extends WebDriverTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/ContentPreviewToggleTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/ContentPreviewToggleTest.php
index ecf96abfc1237d88444dc45bc1b1fd4c29aad64f..ee5dfb1f059d6693019b47efd73a5a6df2fb0ac9 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/ContentPreviewToggleTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/ContentPreviewToggleTest.php
@@ -26,6 +26,11 @@ class ContentPreviewToggleTest extends WebDriverTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/ContextualLinksTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/ContextualLinksTest.php
index ea0d170085c7a37ebdf429debbdafef3b1a8271a..630b9968ce8c86bf19c2a5b2a2ba114fa758d8a9 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/ContextualLinksTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/ContextualLinksTest.php
@@ -28,6 +28,11 @@ class ContextualLinksTest extends WebDriverTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldBlockTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldBlockTest.php
index b0b371fd45d3035cb519480bddbe9fef43225a07..bfde4f09fcdd315ff2d5fc39c36adeaa357d7f94 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldBlockTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/FieldBlockTest.php
@@ -25,6 +25,11 @@ class FieldBlockTest extends WebDriverTestBase {
     'layout_builder_fieldblock_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockPrivateFilesTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockPrivateFilesTest.php
index a0c14e19a4bad56ac5c9917ed3ac3f7610cb8d5f..67f86e4e36902077d7f138bd1a1242b8c78ab0e8 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockPrivateFilesTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockPrivateFilesTest.php
@@ -26,6 +26,11 @@ class InlineBlockPrivateFilesTest extends InlineBlockTestBase {
     'file',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The file system service.
    *
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockTest.php
index a256b253990420ed7853549f0fbe61006ed31de5..a9356bacbaca304ea8c20ee84d3c52cf34d29055 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockTest.php
@@ -12,6 +12,11 @@
  */
 class InlineBlockTest extends InlineBlockTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests adding and editing of inline blocks.
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/ItemLayoutFieldBlockTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/ItemLayoutFieldBlockTest.php
index 5acc2034b3a7b8c96ae09736bde7091bfe219e04..73cb6ca990a9a34fada48a4a183ed614fb7dd15e 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/ItemLayoutFieldBlockTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/ItemLayoutFieldBlockTest.php
@@ -19,6 +19,11 @@ class ItemLayoutFieldBlockTest extends WebDriverTestBase {
     'layout_builder',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php
index 8dcd507c8dac0349fb7f69dfa8775f1dfdf90e41..4445b3ac9531f4bac26683354a80190835e07eae 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderDisableInteractionsTest.php
@@ -32,6 +32,11 @@ class LayoutBuilderDisableInteractionsTest extends WebDriverTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderOptInTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderOptInTest.php
index 03f69a770ed12901efe2e28bc78c26c7b1832079..be8f70d80d16178363e8c486f7358b7431d43a9c 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderOptInTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderOptInTest.php
@@ -20,6 +20,11 @@ class LayoutBuilderOptInTest extends WebDriverTestBase {
     'block',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderQuickEditTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderQuickEditTest.php
index 0f85fcc5b4897a2d718e00ed8c9a8bdd8ea3efd1..3c5fd56ffacb949fd246d4af04cc20a61818faf9 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderQuickEditTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderQuickEditTest.php
@@ -28,6 +28,11 @@ class LayoutBuilderQuickEditTest extends QuickEditJavascriptTestBase {
     'layout_builder',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The article node under test.
    *
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderTest.php
index fa274bc119a541837b2561bd9b45099f2fb2a5b8..f92195c9dc947ad5169b2f7661a88586dc67816a 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderTest.php
@@ -29,6 +29,11 @@ class LayoutBuilderTest extends WebDriverTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The node to customize with Layout Builder.
    *
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderToolbarTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderToolbarTest.php
index f1f61596a2d0274cea74e8d7ce18cb272eeb5464..de54949efc211349116d92e57e29e16b7dceff8a 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderToolbarTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderToolbarTest.php
@@ -22,6 +22,11 @@ class LayoutBuilderToolbarTest extends WebDriverTestBase {
     'toolbar',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderUiTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderUiTest.php
index 5ec449b28a9a80e9a85b562f5f5bcaa9ab6db5b2..85cb669f4214971d7e2e6ee680c7f26462d7aaba 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderUiTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderUiTest.php
@@ -31,6 +31,11 @@ class LayoutBuilderUiTest extends WebDriverTestBase {
     'views',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/MoveBlockFormTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/MoveBlockFormTest.php
index e8cf15f4074b0bdbcbb63f6cc27fcd02aba8871c..7ceb0af8da783611616d29c669778448dfb79cbe 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/MoveBlockFormTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/MoveBlockFormTest.php
@@ -31,6 +31,11 @@ class MoveBlockFormTest extends WebDriverTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/layout_builder/tests/src/FunctionalJavascript/TestMultiWidthLayoutsTest.php b/core/modules/layout_builder/tests/src/FunctionalJavascript/TestMultiWidthLayoutsTest.php
index 86edc44efdfb8d3e93b6b8e4f3edf5587a0d1a94..0049edc1e07443429f1201ebec91ef04468dec46 100644
--- a/core/modules/layout_builder/tests/src/FunctionalJavascript/TestMultiWidthLayoutsTest.php
+++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/TestMultiWidthLayoutsTest.php
@@ -24,6 +24,11 @@ class TestMultiWidthLayoutsTest extends WebDriverTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/link/tests/src/Functional/LinkFieldTest.php b/core/modules/link/tests/src/Functional/LinkFieldTest.php
index fb3680af66fc24ff1ecb2510812f3b7a4ee1e395..fda83fd5646ea991b73cde7223cfae87fe657936 100644
--- a/core/modules/link/tests/src/Functional/LinkFieldTest.php
+++ b/core/modules/link/tests/src/Functional/LinkFieldTest.php
@@ -36,6 +36,11 @@ class LinkFieldTest extends BrowserTestBase {
     'link_test_base_field',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A field to use in this test class.
    *
diff --git a/core/modules/link/tests/src/Functional/LinkFieldUITest.php b/core/modules/link/tests/src/Functional/LinkFieldUITest.php
index 2768770665221722370d375e10ee1a4eac2d0cd5..65e4125dc38e9dc442871424337bf2804fb62e6f 100644
--- a/core/modules/link/tests/src/Functional/LinkFieldUITest.php
+++ b/core/modules/link/tests/src/Functional/LinkFieldUITest.php
@@ -27,6 +27,11 @@ class LinkFieldUITest extends BrowserTestBase {
    */
   public static $modules = ['node', 'link', 'field_ui', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user that can edit content types.
    *
diff --git a/core/modules/link/tests/src/Functional/Views/LinkViewsTokensTest.php b/core/modules/link/tests/src/Functional/Views/LinkViewsTokensTest.php
index b1cce75d0e3abf190a64c6a5707f40667e2751e6..4b9f0e932a9bde452580fa64b09ee1bcb8d6834b 100644
--- a/core/modules/link/tests/src/Functional/Views/LinkViewsTokensTest.php
+++ b/core/modules/link/tests/src/Functional/Views/LinkViewsTokensTest.php
@@ -21,6 +21,11 @@ class LinkViewsTokensTest extends ViewTestBase {
    */
   public static $modules = ['link_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/locale/tests/src/Functional/LocaleConfigTranslationImportTest.php b/core/modules/locale/tests/src/Functional/LocaleConfigTranslationImportTest.php
index 058d9ddf8e77eb495a68b2421e2c150611bd4acc..64dcb705d8a653717392d56287ee6fcb5c24ebec 100644
--- a/core/modules/locale/tests/src/Functional/LocaleConfigTranslationImportTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleConfigTranslationImportTest.php
@@ -20,6 +20,11 @@ class LocaleConfigTranslationImportTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'locale_test_translate'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleConfigTranslationTest.php b/core/modules/locale/tests/src/Functional/LocaleConfigTranslationTest.php
index f3217691d62a553c8737b75ef0bb9ebbacb35221..bc1d914c1c6de5d762b8e261b7b0cad368b769f2 100644
--- a/core/modules/locale/tests/src/Functional/LocaleConfigTranslationTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleConfigTranslationTest.php
@@ -26,6 +26,11 @@ class LocaleConfigTranslationTest extends BrowserTestBase {
    */
   public static $modules = ['locale', 'contact', 'contact_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleContentTest.php b/core/modules/locale/tests/src/Functional/LocaleContentTest.php
index e7955503a437a9a87934f574c8caf1fc06a1139d..9ac40754f80763f03946456166dc19761ba95997 100644
--- a/core/modules/locale/tests/src/Functional/LocaleContentTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleContentTest.php
@@ -21,6 +21,11 @@ class LocaleContentTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Verifies that machine name fields are always LTR.
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleExportTest.php b/core/modules/locale/tests/src/Functional/LocaleExportTest.php
index 1b0d67e88af869efb3ed5f8fab24ce6a84b1c83d..9869fb70a2226dcc1e1589491fad2ac6c7e2af1a 100644
--- a/core/modules/locale/tests/src/Functional/LocaleExportTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleExportTest.php
@@ -19,6 +19,11 @@ class LocaleExportTest extends BrowserTestBase {
    */
   public static $modules = ['locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user able to create languages and export translations.
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleFileSystemFormTest.php b/core/modules/locale/tests/src/Functional/LocaleFileSystemFormTest.php
index c38da43d77fcf5a5ac01c04c7918b71c786d4015..6a866af5115ad7b6d22fbfa1e990741db43c5776 100644
--- a/core/modules/locale/tests/src/Functional/LocaleFileSystemFormTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleFileSystemFormTest.php
@@ -18,6 +18,11 @@ class LocaleFileSystemFormTest extends BrowserTestBase {
    */
   public static $modules = ['system'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleImportFunctionalTest.php b/core/modules/locale/tests/src/Functional/LocaleImportFunctionalTest.php
index 1005c5c2342cb690ebc270af2a4cf86565ccc4f5..11906f3893f17ba8873fee7953b8fac39b4406be 100644
--- a/core/modules/locale/tests/src/Functional/LocaleImportFunctionalTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleImportFunctionalTest.php
@@ -23,6 +23,11 @@ class LocaleImportFunctionalTest extends BrowserTestBase {
    */
   public static $modules = ['locale', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user able to create languages and import translations.
    *
diff --git a/core/modules/locale/tests/src/Functional/LocaleJavascriptTranslationTest.php b/core/modules/locale/tests/src/Functional/LocaleJavascriptTranslationTest.php
index 2219fa46640af901cc5a9095423b90203a3d7496..62036cd8bbdcf69e47aa8286f837a914b8dfb351 100644
--- a/core/modules/locale/tests/src/Functional/LocaleJavascriptTranslationTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleJavascriptTranslationTest.php
@@ -21,6 +21,11 @@ class LocaleJavascriptTranslationTest extends BrowserTestBase {
    */
   public static $modules = ['locale', 'locale_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testFileParsing() {
 
     // This test is for ensuring that the regular expression in
diff --git a/core/modules/locale/tests/src/Functional/LocaleLocaleLookupTest.php b/core/modules/locale/tests/src/Functional/LocaleLocaleLookupTest.php
index 3dd4eadb58da03562e60bc15a8f0c047087cd96d..02edcb7676e0c27afc6e0ef6efb646c291a58f5c 100644
--- a/core/modules/locale/tests/src/Functional/LocaleLocaleLookupTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleLocaleLookupTest.php
@@ -20,6 +20,11 @@ class LocaleLocaleLookupTest extends BrowserTestBase {
    */
   public static $modules = ['locale', 'locale_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleNonInteractiveDevInstallTest.php b/core/modules/locale/tests/src/Functional/LocaleNonInteractiveDevInstallTest.php
index 080616af91ca4515ccf02d0308c4c1297b7cc191..6798f5a9aa19a6e0f336a201b20fe30aa48c6bcd 100644
--- a/core/modules/locale/tests/src/Functional/LocaleNonInteractiveDevInstallTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleNonInteractiveDevInstallTest.php
@@ -9,6 +9,11 @@
  */
 class LocaleNonInteractiveDevInstallTest extends LocaleNonInteractiveInstallTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleNonInteractiveInstallTest.php b/core/modules/locale/tests/src/Functional/LocaleNonInteractiveInstallTest.php
index ee12a6713ae3b000eae65906379012df0c04d025..ea3c1b5aba1f0263079de7db1287a5b824995bfb 100644
--- a/core/modules/locale/tests/src/Functional/LocaleNonInteractiveInstallTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleNonInteractiveInstallTest.php
@@ -11,6 +11,11 @@
  */
 class LocaleNonInteractiveInstallTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Gets the version string to use in the translation file.
    *
diff --git a/core/modules/locale/tests/src/Functional/LocalePathTest.php b/core/modules/locale/tests/src/Functional/LocalePathTest.php
index 588488eb0b2ee65d4b831c62ccc959fbb23224a9..9b1584e44682c71ddb9daf8485d0b118f9af7906 100644
--- a/core/modules/locale/tests/src/Functional/LocalePathTest.php
+++ b/core/modules/locale/tests/src/Functional/LocalePathTest.php
@@ -24,6 +24,11 @@ class LocalePathTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'locale', 'path', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocalePluralFormatTest.php b/core/modules/locale/tests/src/Functional/LocalePluralFormatTest.php
index 0b2a88caed25d1de9e23020fd017c77f222c7a3b..b85e737a06bb1a30f1ffade5235f8572cd3538b6 100644
--- a/core/modules/locale/tests/src/Functional/LocalePluralFormatTest.php
+++ b/core/modules/locale/tests/src/Functional/LocalePluralFormatTest.php
@@ -28,6 +28,11 @@ class LocalePluralFormatTest extends BrowserTestBase {
    */
   public static $modules = ['locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleTranslateStringTourTest.php b/core/modules/locale/tests/src/Functional/LocaleTranslateStringTourTest.php
index ffd5bc7b02f240ff3746e1bffb5adbb1be393216..19db1b38ed2bf92ff6c52a7d784d3f75401f5245 100644
--- a/core/modules/locale/tests/src/Functional/LocaleTranslateStringTourTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleTranslateStringTourTest.php
@@ -25,6 +25,11 @@ class LocaleTranslateStringTourTest extends TourTestBase {
    */
   public static $modules = ['locale', 'tour'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleTranslatedSchemaDefinitionTest.php b/core/modules/locale/tests/src/Functional/LocaleTranslatedSchemaDefinitionTest.php
index 6f292693f82876faf123c5ef9193593ca09ec9f1..71186fa0c3e9899a2cc618c37edb3f8ea53490ee 100644
--- a/core/modules/locale/tests/src/Functional/LocaleTranslatedSchemaDefinitionTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleTranslatedSchemaDefinitionTest.php
@@ -22,6 +22,11 @@ class LocaleTranslatedSchemaDefinitionTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'locale', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleTranslationDownloadTest.php b/core/modules/locale/tests/src/Functional/LocaleTranslationDownloadTest.php
index f97a8d607cfd8f7e14ed3e34d8ce8025d82c3ab4..7b727518a84a15f6e0ebaec257217e4548772ab5 100644
--- a/core/modules/locale/tests/src/Functional/LocaleTranslationDownloadTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleTranslationDownloadTest.php
@@ -20,6 +20,11 @@ class LocaleTranslationDownloadTest extends LocaleUpdateBase {
    */
   protected $translationsStream;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleTranslationUiTest.php b/core/modules/locale/tests/src/Functional/LocaleTranslationUiTest.php
index d9aa561d6b37097a69463fb45b03c3c14a5d045d..f8fe9c6db1c33efc9bca964285025e42aca69958 100644
--- a/core/modules/locale/tests/src/Functional/LocaleTranslationUiTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleTranslationUiTest.php
@@ -24,6 +24,11 @@ class LocaleTranslationUiTest extends BrowserTestBase {
    */
   public static $modules = ['locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Enable interface translation to English.
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleUpdateCronTest.php b/core/modules/locale/tests/src/Functional/LocaleUpdateCronTest.php
index dd167439fa40ba3ecda9d76a89c7e66a733b2250..34ee9dc36a8af98766037ca9759bd458f34bcd15 100644
--- a/core/modules/locale/tests/src/Functional/LocaleUpdateCronTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleUpdateCronTest.php
@@ -16,6 +16,11 @@ class LocaleUpdateCronTest extends LocaleUpdateBase {
 
   protected $batchOutput = [];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleUpdateDevelopmentReleaseTest.php b/core/modules/locale/tests/src/Functional/LocaleUpdateDevelopmentReleaseTest.php
index 5c972d1ef377a699001f688763aa0785223d6591..59211984079397d900f50faa955ba35d3d34f12d 100644
--- a/core/modules/locale/tests/src/Functional/LocaleUpdateDevelopmentReleaseTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleUpdateDevelopmentReleaseTest.php
@@ -13,6 +13,11 @@ class LocaleUpdateDevelopmentReleaseTest extends BrowserTestBase {
 
   public static $modules = ['locale', 'locale_test_development_release'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     module_load_include('compare.inc', 'locale');
diff --git a/core/modules/locale/tests/src/Functional/LocaleUpdateInterfaceTest.php b/core/modules/locale/tests/src/Functional/LocaleUpdateInterfaceTest.php
index dcf1ba08c44c73c5bede33fbdc915fb98c68f277..5c7d698f4240d374529b49b523b0c0f054b46195 100644
--- a/core/modules/locale/tests/src/Functional/LocaleUpdateInterfaceTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleUpdateInterfaceTest.php
@@ -19,6 +19,11 @@ class LocaleUpdateInterfaceTest extends LocaleUpdateBase {
    */
   public static $modules = ['locale_test_translate'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/locale/tests/src/Functional/LocaleUpdateTest.php b/core/modules/locale/tests/src/Functional/LocaleUpdateTest.php
index e7210dc6eed2a2742430a849d3662f984845965f..2c25228d10efca36a68cf4cbc2e3ad450b6dbab5 100644
--- a/core/modules/locale/tests/src/Functional/LocaleUpdateTest.php
+++ b/core/modules/locale/tests/src/Functional/LocaleUpdateTest.php
@@ -12,6 +12,11 @@
  */
 class LocaleUpdateTest extends LocaleUpdateBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/FieldFormatter/OEmbedFormatterTest.php b/core/modules/media/tests/src/Functional/FieldFormatter/OEmbedFormatterTest.php
index 2a0a0959586d1f1bcde997496f6a230f42299714..b4e5767614965e5212624ea1f773d907fd027d25 100644
--- a/core/modules/media/tests/src/Functional/FieldFormatter/OEmbedFormatterTest.php
+++ b/core/modules/media/tests/src/Functional/FieldFormatter/OEmbedFormatterTest.php
@@ -27,6 +27,11 @@ class OEmbedFormatterTest extends MediaFunctionalTestBase {
     'media_test_oembed',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Hal/MediaHalJsonAnonTest.php b/core/modules/media/tests/src/Functional/Hal/MediaHalJsonAnonTest.php
index 2b92c73be2ffae62d99e1a9940f7d9671ac0adb6..6f990b6641d1e4a61127fcc514477b9c784f3621 100644
--- a/core/modules/media/tests/src/Functional/Hal/MediaHalJsonAnonTest.php
+++ b/core/modules/media/tests/src/Functional/Hal/MediaHalJsonAnonTest.php
@@ -22,6 +22,11 @@ class MediaHalJsonAnonTest extends MediaResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Hal/MediaHalJsonBasicAuthTest.php b/core/modules/media/tests/src/Functional/Hal/MediaHalJsonBasicAuthTest.php
index 73d37b377e00b6ead4d682c01a2dece3463967fc..92019bf75f5aed0061f14ec566c07e855a353ebd 100644
--- a/core/modules/media/tests/src/Functional/Hal/MediaHalJsonBasicAuthTest.php
+++ b/core/modules/media/tests/src/Functional/Hal/MediaHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class MediaHalJsonBasicAuthTest extends MediaHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Hal/MediaHalJsonCookieTest.php b/core/modules/media/tests/src/Functional/Hal/MediaHalJsonCookieTest.php
index 798cf39a21c6d44b703900c44f91b6e919a9de55..16a76ec71b2eabd99245fdb190a3d72d33bb4c83 100644
--- a/core/modules/media/tests/src/Functional/Hal/MediaHalJsonCookieTest.php
+++ b/core/modules/media/tests/src/Functional/Hal/MediaHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class MediaHalJsonCookieTest extends MediaHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonAnonTest.php b/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonAnonTest.php
index 6a5611f9c781d2748d35bf2d364a2f0f1268fc33..4618e492c0af325c9e46e82cdf8a99df7e4340df 100644
--- a/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonAnonTest.php
+++ b/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class MediaTypeHalJsonAnonTest extends MediaTypeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonBasicAuthTest.php b/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonBasicAuthTest.php
index 0ef13e995243726c2a96ac02cf2b154acb28008a..3fc0aaba13378067c6465a2f833c57fc738834b4 100644
--- a/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonBasicAuthTest.php
+++ b/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class MediaTypeHalJsonBasicAuthTest extends MediaTypeResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonCookieTest.php b/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonCookieTest.php
index c66b499ef5b3404347324b313421c6537b9662e1..62de7a48b143840d224db320c5cfefa5aa560703 100644
--- a/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonCookieTest.php
+++ b/core/modules/media/tests/src/Functional/Hal/MediaTypeHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class MediaTypeHalJsonCookieTest extends MediaTypeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/MediaAccessTest.php b/core/modules/media/tests/src/Functional/MediaAccessTest.php
index 050c567da84a18acdf11ad2d3b4060dfcf323263..c50f573300f5a6924d081a24f2c976037c442d39 100644
--- a/core/modules/media/tests/src/Functional/MediaAccessTest.php
+++ b/core/modules/media/tests/src/Functional/MediaAccessTest.php
@@ -26,6 +26,11 @@ class MediaAccessTest extends MediaFunctionalTestBase {
     'media_test_source',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/MediaBulkFormTest.php b/core/modules/media/tests/src/Functional/MediaBulkFormTest.php
index fb9caf1fdd799d06f2bc436e78b5741b674fe9a1..5bb70a2a82a06f110d9b20f17cd81d281b2c7f10 100644
--- a/core/modules/media/tests/src/Functional/MediaBulkFormTest.php
+++ b/core/modules/media/tests/src/Functional/MediaBulkFormTest.php
@@ -19,6 +19,11 @@ class MediaBulkFormTest extends MediaFunctionalTestBase {
    */
   public static $modules = ['media_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The test media type.
    *
diff --git a/core/modules/media/tests/src/Functional/MediaCacheTagsTest.php b/core/modules/media/tests/src/Functional/MediaCacheTagsTest.php
index a2c3530abcc183bf19eb842723119c22c9be6541..eb3402fc88cd5113f856330fdade5ae625c050af 100644
--- a/core/modules/media/tests/src/Functional/MediaCacheTagsTest.php
+++ b/core/modules/media/tests/src/Functional/MediaCacheTagsTest.php
@@ -24,6 +24,11 @@ class MediaCacheTagsTest extends EntityWithUriCacheTagsTestBase {
     'media_test_source',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/MediaContextualLinksTest.php b/core/modules/media/tests/src/Functional/MediaContextualLinksTest.php
index 5eeaa95ce8c6d4fd2e87bfff0faa158aae3bfaf3..35c1224c7ed27fa738372d289f609f1ec7404522 100644
--- a/core/modules/media/tests/src/Functional/MediaContextualLinksTest.php
+++ b/core/modules/media/tests/src/Functional/MediaContextualLinksTest.php
@@ -18,6 +18,11 @@ class MediaContextualLinksTest extends MediaFunctionalTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests contextual links.
    */
diff --git a/core/modules/media/tests/src/Functional/MediaInstallTest.php b/core/modules/media/tests/src/Functional/MediaInstallTest.php
index 010f07698a941e9ca64f50b6679b979a316cd389..0811322fb9df620be7b2f50868af8dfedb88327d 100644
--- a/core/modules/media/tests/src/Functional/MediaInstallTest.php
+++ b/core/modules/media/tests/src/Functional/MediaInstallTest.php
@@ -16,6 +16,11 @@ class MediaInstallTest extends BrowserTestBase {
    */
   public static $modules = ['media'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/MediaOverviewPageTest.php b/core/modules/media/tests/src/Functional/MediaOverviewPageTest.php
index f1d574a17ac8789271d33c622c97ce4aac0d3fe8..d4f82eaea0235f23edf399117a501d4d4205ca2d 100644
--- a/core/modules/media/tests/src/Functional/MediaOverviewPageTest.php
+++ b/core/modules/media/tests/src/Functional/MediaOverviewPageTest.php
@@ -13,6 +13,11 @@
  */
 class MediaOverviewPageTest extends MediaFunctionalTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/MediaRevisionTest.php b/core/modules/media/tests/src/Functional/MediaRevisionTest.php
index 75638aeec0a69c2ad88870bc6604386de73ae44b..6ec57bea2cb9f7464ee41c073d8b95abea19ed39 100644
--- a/core/modules/media/tests/src/Functional/MediaRevisionTest.php
+++ b/core/modules/media/tests/src/Functional/MediaRevisionTest.php
@@ -15,6 +15,11 @@
  */
 class MediaRevisionTest extends MediaFunctionalTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Checks media revision operations.
    */
diff --git a/core/modules/media/tests/src/Functional/MediaSettingsTest.php b/core/modules/media/tests/src/Functional/MediaSettingsTest.php
index ba25392f5c6b9da92a1f53773ac5a7d08255c550..0a5a00b2f436cc8e1c5b0ba370407877b52f98f5 100644
--- a/core/modules/media/tests/src/Functional/MediaSettingsTest.php
+++ b/core/modules/media/tests/src/Functional/MediaSettingsTest.php
@@ -9,6 +9,11 @@
  */
 class MediaSettingsTest extends MediaFunctionalTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/MediaSourceFileTest.php b/core/modules/media/tests/src/Functional/MediaSourceFileTest.php
index fad13dc81f043f91f9f1effb5601aab52b546424..55fb9276f321a3dc20c2b0c13b24a952d4bdc87f 100644
--- a/core/modules/media/tests/src/Functional/MediaSourceFileTest.php
+++ b/core/modules/media/tests/src/Functional/MediaSourceFileTest.php
@@ -11,6 +11,11 @@
  */
 class MediaSourceFileTest extends MediaFunctionalTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test that it's possible to change the allowed file extensions.
    */
diff --git a/core/modules/media/tests/src/Functional/MediaTemplateSuggestionsTest.php b/core/modules/media/tests/src/Functional/MediaTemplateSuggestionsTest.php
index 916eb7cfc207ca875bc354e57d817278ea7f0673..eef7ae34cd63fb20954c97ed14712aee2cdcecd3 100644
--- a/core/modules/media/tests/src/Functional/MediaTemplateSuggestionsTest.php
+++ b/core/modules/media/tests/src/Functional/MediaTemplateSuggestionsTest.php
@@ -18,6 +18,11 @@ class MediaTemplateSuggestionsTest extends MediaFunctionalTestBase {
    */
   public static $modules = ['media'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests template suggestions from media_theme_suggestions_media().
    */
diff --git a/core/modules/media/tests/src/Functional/MediaTranslationUITest.php b/core/modules/media/tests/src/Functional/MediaTranslationUITest.php
index 167d76a30ba1e5b839a0a63d28cec341622f99b4..9ac587a5d045090ff55fad28ebcbf8f868e74aac 100644
--- a/core/modules/media/tests/src/Functional/MediaTranslationUITest.php
+++ b/core/modules/media/tests/src/Functional/MediaTranslationUITest.php
@@ -14,6 +14,11 @@ class MediaTranslationUITest extends ContentTranslationUITestBase {
 
   use MediaTypeCreationTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/MediaTypeCreationTest.php b/core/modules/media/tests/src/Functional/MediaTypeCreationTest.php
index 7de1cd8276d9e3e9bd40fdfc2e9b161a372e8b9c..2ced87cf459f39b37f9738234d5d1a603aa83b5f 100644
--- a/core/modules/media/tests/src/Functional/MediaTypeCreationTest.php
+++ b/core/modules/media/tests/src/Functional/MediaTypeCreationTest.php
@@ -18,6 +18,11 @@ class MediaTypeCreationTest extends MediaFunctionalTestBase {
     'media_test_source',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the media type creation form with only the mandatory options.
    */
diff --git a/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php b/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
index 130baa41626cdeed445cf773e26f792043b7a696..dacd9e9fe8d51d19c24e6a0f6adeff6f880f9d9c 100644
--- a/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
+++ b/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
@@ -25,6 +25,11 @@ class MediaUiFunctionalTest extends MediaFunctionalTestBase {
     'media_test_source',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/ProviderRepositoryTest.php b/core/modules/media/tests/src/Functional/ProviderRepositoryTest.php
index d04d46f91c69dff5e5d343018ee14c0059061410..8c583e4ba5a6ea1261a93ac0335db42bd740d9b8 100644
--- a/core/modules/media/tests/src/Functional/ProviderRepositoryTest.php
+++ b/core/modules/media/tests/src/Functional/ProviderRepositoryTest.php
@@ -13,6 +13,11 @@
  */
 class ProviderRepositoryTest extends MediaFunctionalTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that provider discovery fails if the provider database is empty.
    *
diff --git a/core/modules/media/tests/src/Functional/ResourceFetcherTest.php b/core/modules/media/tests/src/Functional/ResourceFetcherTest.php
index e10ef2e209399c8eb521df1c56afb52043ff397c..7aed9b062d34e5f9ca8a8b31a6b55315ed8da5ec 100644
--- a/core/modules/media/tests/src/Functional/ResourceFetcherTest.php
+++ b/core/modules/media/tests/src/Functional/ResourceFetcherTest.php
@@ -16,6 +16,11 @@ class ResourceFetcherTest extends MediaFunctionalTestBase {
 
   use OEmbedTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaJsonAnonTest.php b/core/modules/media/tests/src/Functional/Rest/MediaJsonAnonTest.php
index 0aae16a00d7ec9111ee57cb7ad30b5d437930d27..2576c5551d5747acecbfd75e7df530217df928fb 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaJsonAnonTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaJsonAnonTest.php
@@ -21,4 +21,9 @@ class MediaJsonAnonTest extends MediaResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaJsonBasicAuthTest.php b/core/modules/media/tests/src/Functional/Rest/MediaJsonBasicAuthTest.php
index b124487d427799e2ccdc85520165142cd61266a7..c65a3b2fd6f376a7e63195da5a1ee27fa316a090 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaJsonBasicAuthTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class MediaJsonBasicAuthTest extends MediaResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaJsonCookieTest.php b/core/modules/media/tests/src/Functional/Rest/MediaJsonCookieTest.php
index 9c6786f1340a3d44eb42cb56e68c6a96a0129902..09dd245027b41f8dfede52dc9f29f10da2bd25c6 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaJsonCookieTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaJsonCookieTest.php
@@ -26,4 +26,9 @@ class MediaJsonCookieTest extends MediaResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonAnonTest.php b/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonAnonTest.php
index 6ee494de5296e50756d4e09f6e7a5d6a96e7ff58..0f5066898143d525fee6fa3b425b940328f1c718 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonAnonTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonAnonTest.php
@@ -21,4 +21,9 @@ class MediaTypeJsonAnonTest extends MediaTypeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonBasicAuthTest.php b/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonBasicAuthTest.php
index 84b1a01c87ad1e95cbfa6ecffbd336ee2885aa98..640ad42ef00da04c026f3edc01d6af91562ceafa 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonBasicAuthTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class MediaTypeJsonBasicAuthTest extends MediaTypeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonCookieTest.php b/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonCookieTest.php
index 90c27b2d519e88a7a0299823b532bf49ac5d96c5..9a3d459dec27d92a32cd016351e3ef6a550fc1d0 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonCookieTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaTypeJsonCookieTest.php
@@ -26,4 +26,9 @@ class MediaTypeJsonCookieTest extends MediaTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlAnonTest.php b/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlAnonTest.php
index 083d80a1c1e19b7ac9cf2caf5d827d803b26705c..cd6bc82c45beab14ab7a618be4eb5126eb42e66a 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlAnonTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlAnonTest.php
@@ -23,4 +23,9 @@ class MediaTypeXmlAnonTest extends MediaTypeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlBasicAuthTest.php b/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlBasicAuthTest.php
index 95de21197dc861faaf62b31532b646090af9fb6f..6bd780977235562a6be757b631d846bde590a3bd 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlBasicAuthTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class MediaTypeXmlBasicAuthTest extends MediaTypeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlCookieTest.php b/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlCookieTest.php
index 3b6a53d96ff070d556787edbd909b85cd808ff0c..c28c72311a527aeef70421e08a8c8120cb37f4ec 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlCookieTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaTypeXmlCookieTest.php
@@ -28,4 +28,9 @@ class MediaTypeXmlCookieTest extends MediaTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaXmlAnonTest.php b/core/modules/media/tests/src/Functional/Rest/MediaXmlAnonTest.php
index 787794996ace09df5419b9ef698660b9422ad514..baafbcb3d26280b687a2d9e67d309b8d9f4c5ee2 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaXmlAnonTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaXmlAnonTest.php
@@ -23,4 +23,9 @@ class MediaXmlAnonTest extends MediaResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaXmlBasicAuthTest.php b/core/modules/media/tests/src/Functional/Rest/MediaXmlBasicAuthTest.php
index 971e75f42cadf62456bddb8c363c62f9395e3e1e..9d41af515f928dec38ff5f9c6c2e77728eb32c7f 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaXmlBasicAuthTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class MediaXmlBasicAuthTest extends MediaResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/Functional/Rest/MediaXmlCookieTest.php b/core/modules/media/tests/src/Functional/Rest/MediaXmlCookieTest.php
index f67f7b4f8c0149449be48e6a910eb4d3360cda83..16a36458a9426703e4e33d13763e7c052a17263d 100644
--- a/core/modules/media/tests/src/Functional/Rest/MediaXmlCookieTest.php
+++ b/core/modules/media/tests/src/Functional/Rest/MediaXmlCookieTest.php
@@ -28,4 +28,9 @@ class MediaXmlCookieTest extends MediaResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/media/tests/src/Functional/UrlResolverTest.php b/core/modules/media/tests/src/Functional/UrlResolverTest.php
index 5e4dfc35143bb45b9b8b38f92422b28afa652f19..5073625811c9e744261e17f60ce7d1857a6dba6a 100644
--- a/core/modules/media/tests/src/Functional/UrlResolverTest.php
+++ b/core/modules/media/tests/src/Functional/UrlResolverTest.php
@@ -15,6 +15,11 @@ class UrlResolverTest extends MediaFunctionalTestBase {
 
   use OEmbedTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php b/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
index 40e169cc6981709d5865cdd2b6e4adb13db389de..1a0e7201d4cda2f850a6201ddf639db322ac2d93 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
@@ -75,6 +75,11 @@ class CKEditorIntegrationTest extends WebDriverTestBase {
     'media_test_ckeditor',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaDisplayTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaDisplayTest.php
index 9a150ceaea2b18b14c99e5760659de2eb30eaf31..9c0856670571af3f42fae0101eeeae54657a335a 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaDisplayTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaDisplayTest.php
@@ -17,6 +17,11 @@
  */
 class MediaDisplayTest extends MediaJavascriptTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaEmbedFilterConfigurationUiTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaEmbedFilterConfigurationUiTest.php
index e3eff54025fba2fa880f4ed7f913e6100668bbf6..46d9568848d68b894a182a0660f544171ea96a09 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaEmbedFilterConfigurationUiTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaEmbedFilterConfigurationUiTest.php
@@ -10,6 +10,11 @@
  */
 class MediaEmbedFilterConfigurationUiTest extends MediaJavascriptTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaReferenceFieldHelpTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaReferenceFieldHelpTest.php
index 7c109c1db8a10db075d01e2f893f0713028e307f..c817c790b0ad5601b1cf870cc4ce4e4d8d95f0b6 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaReferenceFieldHelpTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaReferenceFieldHelpTest.php
@@ -11,6 +11,11 @@
  */
 class MediaReferenceFieldHelpTest extends MediaJavascriptTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test our custom help texts when creating a field.
    *
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceAudioVideoTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceAudioVideoTest.php
index 2195f74b3443bb9a94ec3d6099f443ddf9ec1750..a3223c7484d44d22f26c6eae442f79f4cbda329d 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceAudioVideoTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceAudioVideoTest.php
@@ -14,6 +14,11 @@
  */
 class MediaSourceAudioVideoTest extends MediaSourceTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Check the Audio source functionality.
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceFileTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceFileTest.php
index e77c5203cd9c464e99e990366179b836a73aca62..6d9c1f44bd31371fa9dc50f8608fe7b4e8a08423 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceFileTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceFileTest.php
@@ -12,6 +12,11 @@
  */
 class MediaSourceFileTest extends MediaSourceTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests the file media source.
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceImageTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceImageTest.php
index 3b485757e27f1362568e8632825531771fde387c..19233736cced4285fbc997bcc952694e70afc9dd 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceImageTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceImageTest.php
@@ -18,6 +18,11 @@
  */
 class MediaSourceImageTest extends MediaSourceTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests the image media source.
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceOEmbedVideoTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceOEmbedVideoTest.php
index 91f47ca74dc4ab0b668c264390219b3a723026a7..423727136629d450dcc7319becfd2add963748d1 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaSourceOEmbedVideoTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaSourceOEmbedVideoTest.php
@@ -21,6 +21,11 @@ class MediaSourceOEmbedVideoTest extends MediaSourceTestBase {
    */
   public static $modules = ['media_test_oembed'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   use OEmbedTestTrait;
 
   /**
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaStandardProfileTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaStandardProfileTest.php
index b7ddb9ed7e47165758fda7f43bde0a6c06e4f0e7..0453460ba5178c1118507eb198ac99d767433c0a 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaStandardProfileTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaStandardProfileTest.php
@@ -28,6 +28,11 @@ class MediaStandardProfileTest extends MediaJavascriptTestBase {
    */
   public static $modules = ['media_test_oembed'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php
index 42e3511f315b9d1b8a94f43e89663ecd4d932540..a36d263a78b0703db8983bfd3a819ab01074d9dd 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php
@@ -11,6 +11,11 @@
  */
 class MediaTypeCreationTest extends MediaJavascriptTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the source field behavior on the add media type form.
    */
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaUiJavascriptTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaUiJavascriptTest.php
index a00a3c20100c03142cca6b3bb653e216c5847f69..0bf76924205cd90c55ec0a362c446a01088c3139 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaUiJavascriptTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaUiJavascriptTest.php
@@ -24,6 +24,11 @@ class MediaUiJavascriptTest extends MediaJavascriptTestBase {
     'media_test_source',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The test media type.
    *
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaViewsWizardTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaViewsWizardTest.php
index b602137e7d9461bcc930a3c063c485ab2490028c..aafa2884e4bb81f99569ddd0d8852353c3421f2a 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaViewsWizardTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaViewsWizardTest.php
@@ -14,6 +14,11 @@
  */
 class MediaViewsWizardTest extends MediaJavascriptTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests adding a view of media.
    */
diff --git a/core/modules/media_library/tests/src/Functional/MediaLibraryDisplayModeTest.php b/core/modules/media_library/tests/src/Functional/MediaLibraryDisplayModeTest.php
index 705a1d0aef97cc0dfd43999614518560473c2630..7ebc2bb1b1a77c1e0f65ed6c81d1d286ec91f54b 100644
--- a/core/modules/media_library/tests/src/Functional/MediaLibraryDisplayModeTest.php
+++ b/core/modules/media_library/tests/src/Functional/MediaLibraryDisplayModeTest.php
@@ -29,6 +29,11 @@ class MediaLibraryDisplayModeTest extends BrowserTestBase {
     'system',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media_library/tests/src/Functional/SettingsFormTest.php b/core/modules/media_library/tests/src/Functional/SettingsFormTest.php
index 35166eade66f02b8f1db933c1e676969a1b8391d..28cc3e0c153c64c733e216b0e00e2389fa19555f 100644
--- a/core/modules/media_library/tests/src/Functional/SettingsFormTest.php
+++ b/core/modules/media_library/tests/src/Functional/SettingsFormTest.php
@@ -20,6 +20,11 @@ class SettingsFormTest extends BrowserTestBase {
    */
   protected static $modules = ['media_library'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the Media Library settings form.
    */
diff --git a/core/modules/media_library/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php b/core/modules/media_library/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
index 7c43a4eb89c14cc07e60820907f4e98c03d09bb4..57a556fde645de471fd661c481d2f276053e24a5 100644
--- a/core/modules/media_library/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
+++ b/core/modules/media_library/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
@@ -24,6 +24,11 @@ class CKEditorIntegrationTest extends WebDriverTestBase {
   use MediaTypeCreationTrait;
   use TestFileCreationTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The user to use during testing.
    *
diff --git a/core/modules/media_library/tests/src/FunctionalJavascript/ContentModerationTest.php b/core/modules/media_library/tests/src/FunctionalJavascript/ContentModerationTest.php
index dbedfcd620e2e54f29b7c4fd6f018f046ed53a0d..f785235184dc48e9e93e9b72a7fed34c37d6681e 100644
--- a/core/modules/media_library/tests/src/FunctionalJavascript/ContentModerationTest.php
+++ b/core/modules/media_library/tests/src/FunctionalJavascript/ContentModerationTest.php
@@ -35,6 +35,11 @@ class ContentModerationTest extends WebDriverTestBase {
     'views',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * User with the 'administer media' permission.
    *
diff --git a/core/modules/media_library/tests/src/FunctionalJavascript/EmbeddedFormWidgetTest.php b/core/modules/media_library/tests/src/FunctionalJavascript/EmbeddedFormWidgetTest.php
index 9ac5d0e3c80b9b8b0082cf96ec1dc5e6c4c2c5fe..3eacc698ff230599b3770bbfe1fec1bb7ef64b29 100644
--- a/core/modules/media_library/tests/src/FunctionalJavascript/EmbeddedFormWidgetTest.php
+++ b/core/modules/media_library/tests/src/FunctionalJavascript/EmbeddedFormWidgetTest.php
@@ -25,6 +25,11 @@ class EmbeddedFormWidgetTest extends WebDriverTestBase {
     'media_library_test_widget',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media_library/tests/src/FunctionalJavascript/MediaLibraryTest.php b/core/modules/media_library/tests/src/FunctionalJavascript/MediaLibraryTest.php
index 5604fa22d20cb6456d66da43ab0a0cce7cb217ab..87b593f99c3e6dc56de5794ab4e5ca79345f098f 100644
--- a/core/modules/media_library/tests/src/FunctionalJavascript/MediaLibraryTest.php
+++ b/core/modules/media_library/tests/src/FunctionalJavascript/MediaLibraryTest.php
@@ -36,6 +36,11 @@ class MediaLibraryTest extends WebDriverTestBase {
     'media_test_oembed',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/media_library/tests/src/FunctionalJavascript/TranslationsTest.php b/core/modules/media_library/tests/src/FunctionalJavascript/TranslationsTest.php
index ff38ef2a35506c66f225f73eef35b484e1968bb8..0a659b5d8d315e57381cbc47f30371e26252ed42 100644
--- a/core/modules/media_library/tests/src/FunctionalJavascript/TranslationsTest.php
+++ b/core/modules/media_library/tests/src/FunctionalJavascript/TranslationsTest.php
@@ -34,6 +34,11 @@ class TranslationsTest extends WebDriverTestBase {
     'views',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonAnonTest.php b/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonAnonTest.php
index d374d2b5a1f98a7435fe30c6c8f694beb50c14ac..1438c0cba2144fc933bd208d50b64e91ef1be0a7 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonAnonTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class MenuLinkContentHalJsonAnonTest extends MenuLinkContentResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonBasicAuthTest.php b/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonBasicAuthTest.php
index 40e93a0c7b56148e599a693b96fc32abd3142741..d94f3e98a53f35a2af6cd64a28cab664df19e1de 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonBasicAuthTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class MenuLinkContentHalJsonBasicAuthTest extends MenuLinkContentHalJsonAnonTest
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonCookieTest.php b/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonCookieTest.php
index 32cba4ac8cd57cfdfca696ec22b4505ac5f12106..aeb7d858e8a35c796eb6f50ccb2fe9d5b00be8db 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonCookieTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Hal/MenuLinkContentHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class MenuLinkContentHalJsonCookieTest extends MenuLinkContentHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentDeleteFormTest.php b/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentDeleteFormTest.php
index ff829659e3f369a8232c38244036f04a367cc167..942703ae533dfa6b6ed88db541138d70eda1fb73 100644
--- a/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentDeleteFormTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentDeleteFormTest.php
@@ -20,6 +20,11 @@ class MenuLinkContentDeleteFormTest extends BrowserTestBase {
    */
   public static $modules = ['menu_link_content'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentFormTest.php b/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentFormTest.php
index b857667793c819c783c1d1b23ac0627aa20554a0..f205ed794f7615caf7b79f8525059e9b909e97b6 100644
--- a/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentFormTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentFormTest.php
@@ -21,6 +21,11 @@ class MenuLinkContentFormTest extends BrowserTestBase {
     'menu_link_content',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * User with 'administer menu' and 'link to any page' permission.
    *
diff --git a/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentTranslationUITest.php b/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentTranslationUITest.php
index 06d9deb050fd23102afea8f5beeef688b80e8766..badeb9cc002f00df5345e6c88c5225750906ab97 100644
--- a/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentTranslationUITest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/MenuLinkContentTranslationUITest.php
@@ -29,6 +29,11 @@ class MenuLinkContentTranslationUITest extends ContentTranslationUITestBase {
     'menu_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonAnonTest.php b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonAnonTest.php
index fefd6b1d513c79742b832c5cb30ef09c44c85f3d..27ee2909cf710ab815293ac5b4772ae3c20b4a71 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonAnonTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonAnonTest.php
@@ -21,4 +21,9 @@ class MenuLinkContentJsonAnonTest extends MenuLinkContentResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonBasicAuthTest.php b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonBasicAuthTest.php
index 269e94991e1404e0f1b3e87b1d114e7508396669..620da15da24126a26656e19ff4d5389d0fc41974 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonBasicAuthTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class MenuLinkContentJsonBasicAuthTest extends MenuLinkContentResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonCookieTest.php b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonCookieTest.php
index 05679525e781dc6727483a6dcde24d773f47f50b..85deeeb6aeec211d531932fad52012e7cd9bf0c9 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonCookieTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentJsonCookieTest.php
@@ -26,4 +26,9 @@ class MenuLinkContentJsonCookieTest extends MenuLinkContentResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlAnonTest.php b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlAnonTest.php
index 7c39dae81dbd03ab0e5334579c238d4bd1ec8611..a1c1ed25a1e868f6988f932b59d8db62b89b553b 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlAnonTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlAnonTest.php
@@ -23,4 +23,9 @@ class MenuLinkContentXmlAnonTest extends MenuLinkContentResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlBasicAuthTest.php b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlBasicAuthTest.php
index 7bbf966170a1f8227f4e2ff33f12a71157fe2a29..1e4999e6dea5db5279bbd0c7f9a8df8745de1330 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlBasicAuthTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class MenuLinkContentXmlBasicAuthTest extends MenuLinkContentResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlCookieTest.php b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlCookieTest.php
index 8b56dde815c33a68496b5bb93c72339283b6e6ec..310e27c18b033ff368ec74d63bba8dd3fa47a1b0 100644
--- a/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlCookieTest.php
+++ b/core/modules/menu_link_content/tests/src/Functional/Rest/MenuLinkContentXmlCookieTest.php
@@ -28,4 +28,9 @@ class MenuLinkContentXmlCookieTest extends MenuLinkContentResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/menu_ui/tests/src/Functional/MenuCacheTagsTest.php b/core/modules/menu_ui/tests/src/Functional/MenuCacheTagsTest.php
index c0d36690bcab545d6994f3de5201f1eb82cf311d..4adf2a2e306030ea0d845287f872a1bdf8f6027b 100644
--- a/core/modules/menu_ui/tests/src/Functional/MenuCacheTagsTest.php
+++ b/core/modules/menu_ui/tests/src/Functional/MenuCacheTagsTest.php
@@ -19,6 +19,11 @@ class MenuCacheTagsTest extends PageCacheTagsTestBase {
    */
   public static $modules = ['menu_ui', 'block', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests cache tags presence and invalidation of the Menu entity.
    *
diff --git a/core/modules/menu_ui/tests/src/Functional/MenuLinkReorderTest.php b/core/modules/menu_ui/tests/src/Functional/MenuLinkReorderTest.php
index 4d2bba60d055d82620e6494d92243636d7f81a1d..88e515857f15732fab412ef4fa33c19c92c7a926 100644
--- a/core/modules/menu_ui/tests/src/Functional/MenuLinkReorderTest.php
+++ b/core/modules/menu_ui/tests/src/Functional/MenuLinkReorderTest.php
@@ -25,6 +25,11 @@ class MenuLinkReorderTest extends BrowserTestBase {
    */
   public static $modules = ['menu_ui', 'test_page_test', 'node', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test creating, editing, deleting menu links via node form widget.
    */
diff --git a/core/modules/menu_ui/tests/src/Functional/MenuUiContentModerationTest.php b/core/modules/menu_ui/tests/src/Functional/MenuUiContentModerationTest.php
index cc86eeff80f9112978ea667d6a5637e4b1210bd6..6aadd290809fa21ce4f7340b4b9a5dcc4dc99e9e 100644
--- a/core/modules/menu_ui/tests/src/Functional/MenuUiContentModerationTest.php
+++ b/core/modules/menu_ui/tests/src/Functional/MenuUiContentModerationTest.php
@@ -21,6 +21,11 @@ class MenuUiContentModerationTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'content_moderation', 'node', 'menu_ui', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/menu_ui/tests/src/Functional/MenuUiLanguageTest.php b/core/modules/menu_ui/tests/src/Functional/MenuUiLanguageTest.php
index 63ebb40215a8807ea8550b7900f229fc6efebca6..dcdb3277b61110648855d8beac4069293111e17e 100644
--- a/core/modules/menu_ui/tests/src/Functional/MenuUiLanguageTest.php
+++ b/core/modules/menu_ui/tests/src/Functional/MenuUiLanguageTest.php
@@ -30,6 +30,11 @@ class MenuUiLanguageTest extends BrowserTestBase {
     'menu_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/menu_ui/tests/src/Functional/MenuUiNodeTest.php b/core/modules/menu_ui/tests/src/Functional/MenuUiNodeTest.php
index 57a100a5e18bd2f03e2a677b3f64345cb04aaca6..df6a47951dfc884eb9cc3ea8c3337757c5de0dee 100644
--- a/core/modules/menu_ui/tests/src/Functional/MenuUiNodeTest.php
+++ b/core/modules/menu_ui/tests/src/Functional/MenuUiNodeTest.php
@@ -28,6 +28,11 @@ class MenuUiNodeTest extends BrowserTestBase {
    */
   public static $modules = ['menu_ui', 'test_page_test', 'node', 'block', 'locale', 'language', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/menu_ui/tests/src/Functional/MenuUiTest.php b/core/modules/menu_ui/tests/src/Functional/MenuUiTest.php
index 862f1ccb483159b53f61bc7220bbed8ade5d8e20..69114430f2934249dfa250cd66f3a092a0b7a389 100644
--- a/core/modules/menu_ui/tests/src/Functional/MenuUiTest.php
+++ b/core/modules/menu_ui/tests/src/Functional/MenuUiTest.php
@@ -39,6 +39,11 @@ class MenuUiTest extends BrowserTestBase {
     'test_page_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with administration rights.
    *
diff --git a/core/modules/menu_ui/tests/src/Functional/MenuUninstallTest.php b/core/modules/menu_ui/tests/src/Functional/MenuUninstallTest.php
index b2d64cece5c801316726037f67cf3eb0f6d6879a..0415ac9a5043d968958147c736c8cd06ad415475 100644
--- a/core/modules/menu_ui/tests/src/Functional/MenuUninstallTest.php
+++ b/core/modules/menu_ui/tests/src/Functional/MenuUninstallTest.php
@@ -19,6 +19,11 @@ class MenuUninstallTest extends BrowserTestBase {
    */
   public static $modules = ['menu_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests Menu uninstall.
    */
diff --git a/core/modules/menu_ui/tests/src/FunctionalJavascript/MenuUiJavascriptTest.php b/core/modules/menu_ui/tests/src/FunctionalJavascript/MenuUiJavascriptTest.php
index 22959326dca9ca31cfc52fad2caf428b3bf7e5d2..fea04e60bddf0503d80adeef22d955ccf9e1abe5 100644
--- a/core/modules/menu_ui/tests/src/FunctionalJavascript/MenuUiJavascriptTest.php
+++ b/core/modules/menu_ui/tests/src/FunctionalJavascript/MenuUiJavascriptTest.php
@@ -28,6 +28,11 @@ class MenuUiJavascriptTest extends WebDriverTestBase {
     'test_page_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the contextual links on a menu block.
    */
diff --git a/core/modules/migrate/tests/src/Functional/process/DownloadFunctionalTest.php b/core/modules/migrate/tests/src/Functional/process/DownloadFunctionalTest.php
index 28824fb094cdbfec080c6d85bdb1f51084f09003..bf6da018c3a5a69a4fd36e2bebf517d2f51abc32 100644
--- a/core/modules/migrate/tests/src/Functional/process/DownloadFunctionalTest.php
+++ b/core/modules/migrate/tests/src/Functional/process/DownloadFunctionalTest.php
@@ -19,6 +19,11 @@ class DownloadFunctionalTest extends BrowserTestBase {
    */
   public static $modules = ['migrate', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that an exception is thrown bu migration continues with the next row.
    */
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateAccessTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateAccessTest.php
index 3c475e20688fa7d98efe277ed5291bc9c708b9f8..5a568aec0f56e06a27e368d8ce2c62bbd6a809fb 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateAccessTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateAccessTest.php
@@ -18,6 +18,11 @@ class MigrateAccessTest extends BrowserTestBase {
    */
   public static $modules = ['migrate_drupal_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that only user 1 can access the migrate UI.
    */
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeFormStepsTest.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeFormStepsTest.php
index caa60c3438393c103036e9f90ffbf59bbeadc908..4ef2738351fbaeed970ca094bbb572ead882c21e 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeFormStepsTest.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeFormStepsTest.php
@@ -22,6 +22,11 @@ class MigrateUpgradeFormStepsTest extends BrowserTestBase {
    */
   public static $modules = ['migrate_drupal_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Hal/NodeHalJsonAnonTest.php b/core/modules/node/tests/src/Functional/Hal/NodeHalJsonAnonTest.php
index f474c54f7cd1941cdcbc0ec17767222d1eed0f86..10f101eb3ffa1e233354764bae650e3bb3684056 100644
--- a/core/modules/node/tests/src/Functional/Hal/NodeHalJsonAnonTest.php
+++ b/core/modules/node/tests/src/Functional/Hal/NodeHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class NodeHalJsonAnonTest extends NodeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Hal/NodeHalJsonBasicAuthTest.php b/core/modules/node/tests/src/Functional/Hal/NodeHalJsonBasicAuthTest.php
index 0c973a168ef0fee1e39545dc4e48a10c9376ab10..fd238757c888f7c2957d2ddd811af7f3c3af0ece 100644
--- a/core/modules/node/tests/src/Functional/Hal/NodeHalJsonBasicAuthTest.php
+++ b/core/modules/node/tests/src/Functional/Hal/NodeHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class NodeHalJsonBasicAuthTest extends NodeHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Hal/NodeHalJsonCookieTest.php b/core/modules/node/tests/src/Functional/Hal/NodeHalJsonCookieTest.php
index e29a58786f750ca8c0c801c3908dc5f76bf63076..1c49e78c7d4ff6d37caf2e269d735600d34ecde4 100644
--- a/core/modules/node/tests/src/Functional/Hal/NodeHalJsonCookieTest.php
+++ b/core/modules/node/tests/src/Functional/Hal/NodeHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class NodeHalJsonCookieTest extends NodeHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonAnonTest.php b/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonAnonTest.php
index 68f531c89e754d6eb766f6ecb51cf4dff1e0ac0d..8a7e8d9b6ba5416dd50d07e5eafa45b37872888f 100644
--- a/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonAnonTest.php
+++ b/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class NodeTypeHalJsonAnonTest extends NodeTypeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonBasicAuthTest.php b/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonBasicAuthTest.php
index fb7098bdc440d54fa44b29fb6039d6309315e39d..2c8760ba71a806d0d7a69c54ccb53ded3cda2f41 100644
--- a/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonBasicAuthTest.php
+++ b/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class NodeTypeHalJsonBasicAuthTest extends NodeTypeResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonCookieTest.php b/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonCookieTest.php
index 9d7f5a9a32e10b8d0075594a046194ea339eef54..96c7046d0f2ebc971715cdf2236af939009c3dfd 100644
--- a/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonCookieTest.php
+++ b/core/modules/node/tests/src/Functional/Hal/NodeTypeHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class NodeTypeHalJsonCookieTest extends NodeTypeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/MultiStepNodeFormBasicOptionsTest.php b/core/modules/node/tests/src/Functional/MultiStepNodeFormBasicOptionsTest.php
index 7bc1775f4ae341b6fa3a7c82163ca0e468e6ae0c..837d96ce31b4d05d9a3256975af9df6e7b077195 100644
--- a/core/modules/node/tests/src/Functional/MultiStepNodeFormBasicOptionsTest.php
+++ b/core/modules/node/tests/src/Functional/MultiStepNodeFormBasicOptionsTest.php
@@ -12,6 +12,11 @@
  */
 class MultiStepNodeFormBasicOptionsTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The field name to create.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeAccessBaseTableTest.php b/core/modules/node/tests/src/Functional/NodeAccessBaseTableTest.php
index f53465051852945cb01869a6b485f5bcf7087d16..4434b0dfe285c1364a5bd7aab8cc45fbf0e479f6 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessBaseTableTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessBaseTableTest.php
@@ -19,6 +19,11 @@ class NodeAccessBaseTableTest extends NodeTestBase {
    */
   public static $modules = ['node_access_test', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The installation profile to use with this test.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeAccessCacheabilityTest.php b/core/modules/node/tests/src/Functional/NodeAccessCacheabilityTest.php
index 84af1ff18a66ce320a4abba12d32c66a7962d99d..abaee259a1d1cad26e717448467b2efa3d6f0a20 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessCacheabilityTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessCacheabilityTest.php
@@ -23,6 +23,11 @@ class NodeAccessCacheabilityTest extends NodeTestBase {
    */
   public static $modules = ['node_access_test', 'node_access_test_auto_bubbling'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/NodeAccessFieldTest.php b/core/modules/node/tests/src/Functional/NodeAccessFieldTest.php
index f466886f284c5e8b4823a8d20b0e926b6299350b..d92b5ef8a814fb311f884e5e91cbf2e41738c93a 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessFieldTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessFieldTest.php
@@ -19,6 +19,11 @@ class NodeAccessFieldTest extends NodeTestBase {
    */
   public static $modules = ['node_access_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to bypass access content.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeAccessGrantsCacheContextTest.php b/core/modules/node/tests/src/Functional/NodeAccessGrantsCacheContextTest.php
index e0a466e21dc8ad2ad6821a23dce5edb8659ada26..ba9f2bb1547a0c1652694aeb8f93aac4ce4ed46d 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessGrantsCacheContextTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessGrantsCacheContextTest.php
@@ -19,6 +19,11 @@ class NodeAccessGrantsCacheContextTest extends NodeTestBase {
    */
   public static $modules = ['node_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * User with permission to view content.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeAccessLanguageFallbackTest.php b/core/modules/node/tests/src/Functional/NodeAccessLanguageFallbackTest.php
index 4beacc34235aea041b7735a6baa93d0f12b53755..b53e36666d2fadf8c4d222ee0397646c2bfb47b4 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessLanguageFallbackTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessLanguageFallbackTest.php
@@ -18,6 +18,11 @@ class NodeAccessLanguageFallbackTest extends NodeTestBase {
    */
   public static $modules = ['language', 'node_access_test', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/NodeAccessMenuLinkTest.php b/core/modules/node/tests/src/Functional/NodeAccessMenuLinkTest.php
index 5d987b36a17d7a957b239d0bf4999bb5cb015a82..54c912345dc1872cef2e78a8371ff9af5b59a35b 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessMenuLinkTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessMenuLinkTest.php
@@ -18,6 +18,11 @@ class NodeAccessMenuLinkTest extends NodeTestBase {
    */
   public static $modules = ['menu_ui', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to manage menu links and create nodes.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeAccessPagerTest.php b/core/modules/node/tests/src/Functional/NodeAccessPagerTest.php
index 6e7e0f216a4d6279fa174895859c5b298ba66c81..ba993d46ef205a45dd43d16c49a9cc301e87bdd4 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessPagerTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessPagerTest.php
@@ -23,6 +23,11 @@ class NodeAccessPagerTest extends BrowserTestBase {
    */
   public static $modules = ['node_access_test', 'comment', 'forum'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodeAccessRebuildNodeGrantsTest.php b/core/modules/node/tests/src/Functional/NodeAccessRebuildNodeGrantsTest.php
index 7ed8413fc7984c37cc4fbec7cf81dfda42471fc1..0e2c6e33dfb8a46c68a2d0bca25798294d765245 100644
--- a/core/modules/node/tests/src/Functional/NodeAccessRebuildNodeGrantsTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAccessRebuildNodeGrantsTest.php
@@ -12,6 +12,11 @@
  */
 class NodeAccessRebuildNodeGrantsTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user to create nodes that only it has access to.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeActionsConfigurationTest.php b/core/modules/node/tests/src/Functional/NodeActionsConfigurationTest.php
index d026902f570f021454e2cbe9280435e50a776817..a93ffb065942fc24f2f81fa57c23dc33726abc54 100644
--- a/core/modules/node/tests/src/Functional/NodeActionsConfigurationTest.php
+++ b/core/modules/node/tests/src/Functional/NodeActionsConfigurationTest.php
@@ -19,6 +19,11 @@ class NodeActionsConfigurationTest extends BrowserTestBase {
    */
   public static $modules = ['action', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests configuration of the node_assign_owner_action action.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeAdminTest.php b/core/modules/node/tests/src/Functional/NodeAdminTest.php
index 24c62dda68b89e71eff03679a28ac63374b79492..9cbb42d9d1fc154affa4500a5cbc6d4c65cf0423 100644
--- a/core/modules/node/tests/src/Functional/NodeAdminTest.php
+++ b/core/modules/node/tests/src/Functional/NodeAdminTest.php
@@ -11,6 +11,12 @@
  * @group node
  */
 class NodeAdminTest extends NodeTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with permission to bypass access content.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeBlockFunctionalTest.php b/core/modules/node/tests/src/Functional/NodeBlockFunctionalTest.php
index cc8e5703bb76e5767fd5f0ea007599a034f8b82a..dc0dfb2ab5f6e66b3e37ba5574f242a919518fd2 100644
--- a/core/modules/node/tests/src/Functional/NodeBlockFunctionalTest.php
+++ b/core/modules/node/tests/src/Functional/NodeBlockFunctionalTest.php
@@ -17,6 +17,11 @@ class NodeBlockFunctionalTest extends NodeTestBase {
 
   use AssertPageCacheContextsAndTagsTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An administrative user for testing.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeCacheTagsTest.php b/core/modules/node/tests/src/Functional/NodeCacheTagsTest.php
index cae058bd5b4ca831db0aa640219b78871984749b..14c02669da13fa6169acb96a4e22b2a906800a21 100644
--- a/core/modules/node/tests/src/Functional/NodeCacheTagsTest.php
+++ b/core/modules/node/tests/src/Functional/NodeCacheTagsTest.php
@@ -19,6 +19,11 @@ class NodeCacheTagsTest extends EntityWithUriCacheTagsTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/NodeContextualLinksTest.php b/core/modules/node/tests/src/Functional/NodeContextualLinksTest.php
index 0d4aabe6a089077be0103b5681be1b44d4d106e7..a27bdc0dec63e79127f49016760de139a3ee5e2e 100644
--- a/core/modules/node/tests/src/Functional/NodeContextualLinksTest.php
+++ b/core/modules/node/tests/src/Functional/NodeContextualLinksTest.php
@@ -18,6 +18,11 @@ class NodeContextualLinksTest extends NodeTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests contextual links.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeCreationTest.php b/core/modules/node/tests/src/Functional/NodeCreationTest.php
index b574e58925fb191a3f9f45e19c1b08194e5d9fd9..fd1e2cbd676803acb7e4c95837159473a1cfe5dc 100644
--- a/core/modules/node/tests/src/Functional/NodeCreationTest.php
+++ b/core/modules/node/tests/src/Functional/NodeCreationTest.php
@@ -23,6 +23,11 @@ class NodeCreationTest extends NodeTestBase {
    */
   public static $modules = ['node_test_exception', 'dblog', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodeDisplayConfigurableTest.php b/core/modules/node/tests/src/Functional/NodeDisplayConfigurableTest.php
index 5bac9abfa953eee18ffd569b4bdd0ce1bd4fe977..9193b6efc95568c03f77d7b4edda350790305856 100644
--- a/core/modules/node/tests/src/Functional/NodeDisplayConfigurableTest.php
+++ b/core/modules/node/tests/src/Functional/NodeDisplayConfigurableTest.php
@@ -18,6 +18,11 @@ class NodeDisplayConfigurableTest extends NodeTestBase {
    */
   public static $modules = ['quickedit', 'rdf'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Sets base fields to configurable display and check settings are respected.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeEditFormTest.php b/core/modules/node/tests/src/Functional/NodeEditFormTest.php
index 014f981363617486c72d213e91e2fa45897a73d1..b4dcc31ba8e7fb3ffd590b9ed52dfe804e3b1e73 100644
--- a/core/modules/node/tests/src/Functional/NodeEditFormTest.php
+++ b/core/modules/node/tests/src/Functional/NodeEditFormTest.php
@@ -12,6 +12,11 @@
  */
 class NodeEditFormTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A normal logged in user.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeEntityViewModeAlterTest.php b/core/modules/node/tests/src/Functional/NodeEntityViewModeAlterTest.php
index be0f1c062305b567a32aff69653a4a37b8c70506..c51af5d42c2bb0a93e2250ae3f56e6566faa5377 100644
--- a/core/modules/node/tests/src/Functional/NodeEntityViewModeAlterTest.php
+++ b/core/modules/node/tests/src/Functional/NodeEntityViewModeAlterTest.php
@@ -19,6 +19,11 @@ class NodeEntityViewModeAlterTest extends NodeTestBase {
    */
   public static $modules = ['node_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Create a "Basic page" node and verify its consistency in the database.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeFieldMultilingualTest.php b/core/modules/node/tests/src/Functional/NodeFieldMultilingualTest.php
index 771426d025a50b6a4bb44ea7a666dbc91cc82ee4..7b77d5c6277f6ef49bf0d63bf2ccd05c03d20c5e 100644
--- a/core/modules/node/tests/src/Functional/NodeFieldMultilingualTest.php
+++ b/core/modules/node/tests/src/Functional/NodeFieldMultilingualTest.php
@@ -22,6 +22,11 @@ class NodeFieldMultilingualTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodeFormSaveChangedTimeTest.php b/core/modules/node/tests/src/Functional/NodeFormSaveChangedTimeTest.php
index 607e68cf0d25b4eeda63e7c49785e19b7a291019..6dfd5a73c28487dcb7353916330f1bb05cdcc0bc 100644
--- a/core/modules/node/tests/src/Functional/NodeFormSaveChangedTimeTest.php
+++ b/core/modules/node/tests/src/Functional/NodeFormSaveChangedTimeTest.php
@@ -20,6 +20,11 @@ class NodeFormSaveChangedTimeTest extends BrowserTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An user with permissions to create and edit articles.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeHelpTest.php b/core/modules/node/tests/src/Functional/NodeHelpTest.php
index 4dad41618536db37b89c91e7a1842ee05d25dd73..971030078220ecf16adcae188ab80aa058485b21 100644
--- a/core/modules/node/tests/src/Functional/NodeHelpTest.php
+++ b/core/modules/node/tests/src/Functional/NodeHelpTest.php
@@ -18,6 +18,11 @@ class NodeHelpTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'node', 'help'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the test node type to create.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeLinksTest.php b/core/modules/node/tests/src/Functional/NodeLinksTest.php
index 730ba47729a0e982b2087945019a6fa4a75108c4..31b222d5aabfe0b470e6cc1a4ac5841bb62651fb 100644
--- a/core/modules/node/tests/src/Functional/NodeLinksTest.php
+++ b/core/modules/node/tests/src/Functional/NodeLinksTest.php
@@ -18,6 +18,11 @@ class NodeLinksTest extends NodeTestBase {
    */
   public static $modules = ['views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that the links can be hidden in the view display settings.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeLoadMultipleTest.php b/core/modules/node/tests/src/Functional/NodeLoadMultipleTest.php
index f19d705448848948c5bae540f718c765c6c8ed6b..fa2b3deceb8c4b8faaccb4449c5b4ab88ba6972d 100644
--- a/core/modules/node/tests/src/Functional/NodeLoadMultipleTest.php
+++ b/core/modules/node/tests/src/Functional/NodeLoadMultipleTest.php
@@ -19,6 +19,11 @@ class NodeLoadMultipleTest extends NodeTestBase {
    */
   public static $modules = ['views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $web_user = $this->drupalCreateUser(['create article content', 'create page content']);
diff --git a/core/modules/node/tests/src/Functional/NodePostSettingsTest.php b/core/modules/node/tests/src/Functional/NodePostSettingsTest.php
index 4716b30067ff9ed8b33af72cd1fff38708daabbb..c46558ef7fbb44583d72d1f8ad64f743ad0bef9e 100644
--- a/core/modules/node/tests/src/Functional/NodePostSettingsTest.php
+++ b/core/modules/node/tests/src/Functional/NodePostSettingsTest.php
@@ -10,6 +10,11 @@
  */
 class NodePostSettingsTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodePreviewAnonymousTest.php b/core/modules/node/tests/src/Functional/NodePreviewAnonymousTest.php
index f10d8b7389d66d1b2008376a2f38186d2d1aeb8d..ff86d237d9a35e47dfc361542e0fe2f5c4611dad 100644
--- a/core/modules/node/tests/src/Functional/NodePreviewAnonymousTest.php
+++ b/core/modules/node/tests/src/Functional/NodePreviewAnonymousTest.php
@@ -20,6 +20,11 @@ class NodePreviewAnonymousTest extends BrowserTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/NodeQueryAlterTest.php b/core/modules/node/tests/src/Functional/NodeQueryAlterTest.php
index 787def2767d86d85a309c1b11123ab29df038823..d7a0054edc0033ec9e7303de626a817db9daa7e0 100644
--- a/core/modules/node/tests/src/Functional/NodeQueryAlterTest.php
+++ b/core/modules/node/tests/src/Functional/NodeQueryAlterTest.php
@@ -18,6 +18,11 @@ class NodeQueryAlterTest extends NodeTestBase {
    */
   public static $modules = ['node_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * User with permission to view content.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeRSSContentTest.php b/core/modules/node/tests/src/Functional/NodeRSSContentTest.php
index 0efa336adecb8d71cf4b74986cc4e920b58efc4a..6dd1592228a943892436c80d9938e98946c414ea 100644
--- a/core/modules/node/tests/src/Functional/NodeRSSContentTest.php
+++ b/core/modules/node/tests/src/Functional/NodeRSSContentTest.php
@@ -22,6 +22,11 @@ class NodeRSSContentTest extends NodeTestBase {
    */
   public static $modules = ['node_test', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodeRevisionPermissionsTest.php b/core/modules/node/tests/src/Functional/NodeRevisionPermissionsTest.php
index 2257b8cfc3f8c465aa85f7d0e3fa265d1ef920ad..3418bcb269eeeda5a19838b19d4d3bf107eb6340 100644
--- a/core/modules/node/tests/src/Functional/NodeRevisionPermissionsTest.php
+++ b/core/modules/node/tests/src/Functional/NodeRevisionPermissionsTest.php
@@ -13,6 +13,11 @@ class NodeRevisionPermissionsTest extends NodeTestBase {
 
   use GeneratePermutationsTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The node revisions.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeRevisionsAllTest.php b/core/modules/node/tests/src/Functional/NodeRevisionsAllTest.php
index ba95a5eb3a210548a6842b38996e2aefc3cab0b8..85440bbfcd41e9e40dc2a98e89b1d3f3a0f052a8 100644
--- a/core/modules/node/tests/src/Functional/NodeRevisionsAllTest.php
+++ b/core/modules/node/tests/src/Functional/NodeRevisionsAllTest.php
@@ -13,6 +13,11 @@
  */
 class NodeRevisionsAllTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A list of nodes created to be used as starting point of different tests.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeRevisionsTest.php b/core/modules/node/tests/src/Functional/NodeRevisionsTest.php
index 9571f79fa64cfc6d051921c3448fe821d624ec33..55d6f86721c4c14e8086d4de382af0348e4f5a4c 100644
--- a/core/modules/node/tests/src/Functional/NodeRevisionsTest.php
+++ b/core/modules/node/tests/src/Functional/NodeRevisionsTest.php
@@ -19,6 +19,11 @@
  */
 class NodeRevisionsTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An array of node revisions.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeRevisionsUiBypassAccessTest.php b/core/modules/node/tests/src/Functional/NodeRevisionsUiBypassAccessTest.php
index 7d58b339277d317f05e9cfe214ac91ff072ac033..d63bb7dca39cba3e7e58bbd27a90c904e1592f5f 100644
--- a/core/modules/node/tests/src/Functional/NodeRevisionsUiBypassAccessTest.php
+++ b/core/modules/node/tests/src/Functional/NodeRevisionsUiBypassAccessTest.php
@@ -15,6 +15,11 @@
  */
 class NodeRevisionsUiBypassAccessTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * User with bypass node access permission.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeRevisionsUiTest.php b/core/modules/node/tests/src/Functional/NodeRevisionsUiTest.php
index 8d52571b95b869e6e98d553d70a4a6b152466877..861833a45dc3e8f99c4a0385d3b0a0d2a25c1a19 100644
--- a/core/modules/node/tests/src/Functional/NodeRevisionsUiTest.php
+++ b/core/modules/node/tests/src/Functional/NodeRevisionsUiTest.php
@@ -14,6 +14,11 @@
  */
 class NodeRevisionsUiTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @var \Drupal\user\Entity\User
    */
diff --git a/core/modules/node/tests/src/Functional/NodeSaveTest.php b/core/modules/node/tests/src/Functional/NodeSaveTest.php
index 64b38610d60c91891c85be4150f8983b71e738c9..d0583b9a4be12047457b779f0717ad252fa4a938 100644
--- a/core/modules/node/tests/src/Functional/NodeSaveTest.php
+++ b/core/modules/node/tests/src/Functional/NodeSaveTest.php
@@ -25,6 +25,11 @@ class NodeSaveTest extends NodeTestBase {
    */
   public static $modules = ['node_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodeSyndicateBlockTest.php b/core/modules/node/tests/src/Functional/NodeSyndicateBlockTest.php
index c1daef94c91b70c12cf10d887c80df4bff38bd42..f39bb7845579427417b7acee22aabcee15537866 100644
--- a/core/modules/node/tests/src/Functional/NodeSyndicateBlockTest.php
+++ b/core/modules/node/tests/src/Functional/NodeSyndicateBlockTest.php
@@ -16,6 +16,11 @@ class NodeSyndicateBlockTest extends NodeTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodeTemplateSuggestionsTest.php b/core/modules/node/tests/src/Functional/NodeTemplateSuggestionsTest.php
index 371cf1c32d6d631164ceca359437d220971374cc..1e73f7a9e789b917e362c0e3d580279e02c74b49 100644
--- a/core/modules/node/tests/src/Functional/NodeTemplateSuggestionsTest.php
+++ b/core/modules/node/tests/src/Functional/NodeTemplateSuggestionsTest.php
@@ -9,6 +9,11 @@
  */
 class NodeTemplateSuggestionsTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if template_preprocess_node() generates the correct suggestions.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeTitleTest.php b/core/modules/node/tests/src/Functional/NodeTitleTest.php
index 7985f65ea5e41c60e225f29b17eca1d159f80d1b..0e490320e5fbcaa0afe22b31a8c432c760e0d9a7 100644
--- a/core/modules/node/tests/src/Functional/NodeTitleTest.php
+++ b/core/modules/node/tests/src/Functional/NodeTitleTest.php
@@ -21,6 +21,11 @@ class NodeTitleTest extends NodeTestBase {
    */
   public static $modules = ['comment', 'views', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with permission to bypass access content.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeTitleXSSTest.php b/core/modules/node/tests/src/Functional/NodeTitleXSSTest.php
index 4b750875a2c688878faaf76750e591df0286f88d..a5302e7042ce2237860630e4c2e807609d9d33ed 100644
--- a/core/modules/node/tests/src/Functional/NodeTitleXSSTest.php
+++ b/core/modules/node/tests/src/Functional/NodeTitleXSSTest.php
@@ -12,6 +12,11 @@
  */
 class NodeTitleXSSTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests XSS functionality with a node entity.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeTranslationUITest.php b/core/modules/node/tests/src/Functional/NodeTranslationUITest.php
index 42ca891322232a558fb2c531a46e3743ed759601..2201d727d8d3d94a41654f79bfd64c2ea99ba624 100644
--- a/core/modules/node/tests/src/Functional/NodeTranslationUITest.php
+++ b/core/modules/node/tests/src/Functional/NodeTranslationUITest.php
@@ -18,6 +18,11 @@
  */
 class NodeTranslationUITest extends ContentTranslationUITestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/NodeTypeInitialLanguageTest.php b/core/modules/node/tests/src/Functional/NodeTypeInitialLanguageTest.php
index 9c442fd5dadebf4aba200b87ea91bda68a133e52..70141772ebdee74d21e3e6e3677387e602756085 100644
--- a/core/modules/node/tests/src/Functional/NodeTypeInitialLanguageTest.php
+++ b/core/modules/node/tests/src/Functional/NodeTypeInitialLanguageTest.php
@@ -18,6 +18,11 @@ class NodeTypeInitialLanguageTest extends NodeTestBase {
    */
   public static $modules = ['language', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/node/tests/src/Functional/NodeTypeTest.php b/core/modules/node/tests/src/Functional/NodeTypeTest.php
index 41f15c0becb37e08f9baa97c6ff8ba9ad568b647..2977c5970f1b117e9b64a8fdee22de1c01a9cd82 100644
--- a/core/modules/node/tests/src/Functional/NodeTypeTest.php
+++ b/core/modules/node/tests/src/Functional/NodeTypeTest.php
@@ -25,6 +25,11 @@ class NodeTypeTest extends NodeTestBase {
    */
   public static $modules = ['field_ui', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Ensures that node type functions (node_type_get_*) work correctly.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeTypeTranslationTest.php b/core/modules/node/tests/src/Functional/NodeTypeTranslationTest.php
index 973955c5dd97e131df10b32cf5c736766234ba7f..925a5f5fcfc72a2118ff940f0a3db2c1de6b94cb 100644
--- a/core/modules/node/tests/src/Functional/NodeTypeTranslationTest.php
+++ b/core/modules/node/tests/src/Functional/NodeTypeTranslationTest.php
@@ -28,6 +28,11 @@ class NodeTypeTranslationTest extends BrowserTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The default language code to use in this test.
    *
diff --git a/core/modules/node/tests/src/Functional/NodeViewLanguageTest.php b/core/modules/node/tests/src/Functional/NodeViewLanguageTest.php
index e6d466b175e322a48e82454137814490f6030e53..5876175a76690a7adfb9a278354410e8a721fcc1 100644
--- a/core/modules/node/tests/src/Functional/NodeViewLanguageTest.php
+++ b/core/modules/node/tests/src/Functional/NodeViewLanguageTest.php
@@ -18,6 +18,11 @@ class NodeViewLanguageTest extends NodeTestBase {
    */
   public static $modules = ['node', 'datetime', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the language extra field display.
    */
diff --git a/core/modules/node/tests/src/Functional/NodeViewTest.php b/core/modules/node/tests/src/Functional/NodeViewTest.php
index 8704d71570ad433aeea18561a47fa12509403b06..708adb59d64ca0b224a48e22a461a8f6c75d5b54 100644
--- a/core/modules/node/tests/src/Functional/NodeViewTest.php
+++ b/core/modules/node/tests/src/Functional/NodeViewTest.php
@@ -12,6 +12,11 @@
  */
 class NodeViewTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests the html head links.
    */
diff --git a/core/modules/node/tests/src/Functional/PagePreviewTest.php b/core/modules/node/tests/src/Functional/PagePreviewTest.php
index 26fc64b17e47b58111579d940ccc605561647352..428ae121aa0e2718313e34dd45b1070808c63e7e 100644
--- a/core/modules/node/tests/src/Functional/PagePreviewTest.php
+++ b/core/modules/node/tests/src/Functional/PagePreviewTest.php
@@ -34,6 +34,11 @@ class PagePreviewTest extends NodeTestBase {
    */
   public static $modules = ['node', 'taxonomy', 'comment', 'image', 'file', 'text', 'node_test', 'menu_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The name of the created field.
    *
diff --git a/core/modules/node/tests/src/Functional/PageViewTest.php b/core/modules/node/tests/src/Functional/PageViewTest.php
index 1f796d83c7cf0a9fcb9d5478a5cd3a8d256415a6..30a8dbdfc0b203d8239e346bb0639a74cc5a27e9 100644
--- a/core/modules/node/tests/src/Functional/PageViewTest.php
+++ b/core/modules/node/tests/src/Functional/PageViewTest.php
@@ -11,6 +11,11 @@
  */
 class PageViewTest extends NodeTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests an anonymous and unpermissioned user attempting to edit the node.
    */
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeJsonAnonTest.php b/core/modules/node/tests/src/Functional/Rest/NodeJsonAnonTest.php
index fa44d1386fcde23c98f4ca9521737577f95dc357..f434b3b87cf003c8e0230e808c9950967aba5015 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeJsonAnonTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeJsonAnonTest.php
@@ -21,4 +21,9 @@ class NodeJsonAnonTest extends NodeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeJsonBasicAuthTest.php b/core/modules/node/tests/src/Functional/Rest/NodeJsonBasicAuthTest.php
index d4ce479c2166e1d3a01898138e310e57656502c2..a0bbdfef053e14f8aacde00e58c60b4bd78dc246 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeJsonBasicAuthTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class NodeJsonBasicAuthTest extends NodeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeJsonCookieTest.php b/core/modules/node/tests/src/Functional/Rest/NodeJsonCookieTest.php
index 0e070bc4d1cd5025c4fa331bc3908d0d509f2462..3cb12de77652a71eddb6395fbf611fd1198d902e 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeJsonCookieTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeJsonCookieTest.php
@@ -26,4 +26,9 @@ class NodeJsonCookieTest extends NodeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonAnonTest.php b/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonAnonTest.php
index ab30b17fe5c59ee9113946c454128d7b0e44b710..1b8970820ec3e9e5b6dfb9407fb7527c4cc75260 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonAnonTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonAnonTest.php
@@ -21,4 +21,9 @@ class NodeTypeJsonAnonTest extends NodeTypeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonBasicAuthTest.php b/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonBasicAuthTest.php
index e1874e4cc638187ef2a39622480de6f64f2085e9..870f0d0be261defe9ff0268edfab8720bdd0ffa6 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonBasicAuthTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class NodeTypeJsonBasicAuthTest extends NodeTypeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonCookieTest.php b/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonCookieTest.php
index 26608fc7046a81d0a7d832bc0359e44e4455fe3d..a280615a5850f2de75959d502f143e642adff704 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonCookieTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeTypeJsonCookieTest.php
@@ -26,4 +26,9 @@ class NodeTypeJsonCookieTest extends NodeTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlAnonTest.php b/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlAnonTest.php
index c21a9d458bc6d94d904dede60724c2da7b303db0..24b2f66e9933e8315f5f9107219def75d2b69b39 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlAnonTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlAnonTest.php
@@ -23,4 +23,9 @@ class NodeTypeXmlAnonTest extends NodeTypeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlBasicAuthTest.php b/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlBasicAuthTest.php
index 29413dc9c2e9f9441db264e8041a4f1646ef55a7..05fb962d7d474b5dd2ef036b41b6e3c9373d1fa1 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlBasicAuthTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class NodeTypeXmlBasicAuthTest extends NodeTypeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlCookieTest.php b/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlCookieTest.php
index 1326f291ffff58eb65f4972367e246d95826c38e..61b21bb98707c4aea0ea5526ea905f469b71f1c5 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlCookieTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeTypeXmlCookieTest.php
@@ -28,4 +28,9 @@ class NodeTypeXmlCookieTest extends NodeTypeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeXmlAnonTest.php b/core/modules/node/tests/src/Functional/Rest/NodeXmlAnonTest.php
index 83e98a1712755acb72fc1907678786e65af5c8a8..5e7716436b9fec3a40eb359ff59020f7e0710a3b 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeXmlAnonTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeXmlAnonTest.php
@@ -23,6 +23,11 @@ class NodeXmlAnonTest extends NodeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeXmlBasicAuthTest.php b/core/modules/node/tests/src/Functional/Rest/NodeXmlBasicAuthTest.php
index ce809747aa73960b294efa67cfcea55645b9bec7..9c738ee6be9cb524bceb609a233131bb7f0669bc 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeXmlBasicAuthTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class NodeXmlBasicAuthTest extends NodeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Rest/NodeXmlCookieTest.php b/core/modules/node/tests/src/Functional/Rest/NodeXmlCookieTest.php
index 288d5a143c3629c66420391cae72a2d048d0b4d3..dc479c932d1153a194d49e130ec70739a3adb982 100644
--- a/core/modules/node/tests/src/Functional/Rest/NodeXmlCookieTest.php
+++ b/core/modules/node/tests/src/Functional/Rest/NodeXmlCookieTest.php
@@ -28,6 +28,11 @@ class NodeXmlCookieTest extends NodeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Views/BulkFormAccessTest.php b/core/modules/node/tests/src/Functional/Views/BulkFormAccessTest.php
index a51fe21b7477675c2e9ce9ba78889724f02932cb..1b440cf2f20dff1e9b07f6aae54b995b74696a45 100644
--- a/core/modules/node/tests/src/Functional/Views/BulkFormAccessTest.php
+++ b/core/modules/node/tests/src/Functional/Views/BulkFormAccessTest.php
@@ -24,6 +24,11 @@ class BulkFormAccessTest extends NodeTestBase {
    */
   public static $modules = ['node_test_views', 'node_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/BulkFormTest.php b/core/modules/node/tests/src/Functional/Views/BulkFormTest.php
index 823093b9064972d375d55655a81d1ad76ceef1c5..1ff8c65f8282207e5ff7d3ec7c781a4e0aed85cc 100644
--- a/core/modules/node/tests/src/Functional/Views/BulkFormTest.php
+++ b/core/modules/node/tests/src/Functional/Views/BulkFormTest.php
@@ -21,6 +21,11 @@ class BulkFormTest extends NodeTestBase {
    */
   public static $modules = ['node_test_views', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/FilterNodeAccessTest.php b/core/modules/node/tests/src/Functional/Views/FilterNodeAccessTest.php
index f51959062467cc13cbde95b35556a6ce4c7c1465..e5597d07baa86f40c7e67b3307a56dd3a8cb014d 100644
--- a/core/modules/node/tests/src/Functional/Views/FilterNodeAccessTest.php
+++ b/core/modules/node/tests/src/Functional/Views/FilterNodeAccessTest.php
@@ -24,6 +24,11 @@ class FilterNodeAccessTest extends NodeTestBase {
    */
   public static $modules = ['node_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/FrontPageTest.php b/core/modules/node/tests/src/Functional/Views/FrontPageTest.php
index 062bbe010fd11e75e81eb872edaaeb6ff2c63057..b7eed1408518f1a95bc10501f3d02df4ac3b3189 100644
--- a/core/modules/node/tests/src/Functional/Views/FrontPageTest.php
+++ b/core/modules/node/tests/src/Functional/Views/FrontPageTest.php
@@ -21,6 +21,11 @@ class FrontPageTest extends ViewTestBase {
 
   use AssertViewsCacheTagsTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/Functional/Views/NodeContextualLinksTest.php b/core/modules/node/tests/src/Functional/Views/NodeContextualLinksTest.php
index 73ccfef7582afc4d5176dcb686a1ab0a25e99a9d..9dad4459c64b915035d44c7c8327b976c0ef0907 100644
--- a/core/modules/node/tests/src/Functional/Views/NodeContextualLinksTest.php
+++ b/core/modules/node/tests/src/Functional/Views/NodeContextualLinksTest.php
@@ -18,6 +18,11 @@ class NodeContextualLinksTest extends NodeTestBase {
    */
   public static $modules = ['contextual'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if the node page works if Contextual Links is disabled.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/NodeFieldFilterTest.php b/core/modules/node/tests/src/Functional/Views/NodeFieldFilterTest.php
index 154985deaace5185fd5e73aedd69797d13c8a0f8..43cf14e2257ecff19e9ef6862d136420675632cc 100644
--- a/core/modules/node/tests/src/Functional/Views/NodeFieldFilterTest.php
+++ b/core/modules/node/tests/src/Functional/Views/NodeFieldFilterTest.php
@@ -16,6 +16,11 @@ class NodeFieldFilterTest extends NodeTestBase {
    */
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/NodeFieldTokensTest.php b/core/modules/node/tests/src/Functional/Views/NodeFieldTokensTest.php
index fc547ed370b0e36bcd434c54ca1ab3c585119f70..4e32b723ab97cb8f0cf79a39d17a47e333917cc7 100644
--- a/core/modules/node/tests/src/Functional/Views/NodeFieldTokensTest.php
+++ b/core/modules/node/tests/src/Functional/Views/NodeFieldTokensTest.php
@@ -20,6 +20,11 @@ class NodeFieldTokensTest extends NodeTestBase {
    */
   public static $testViews = ['test_node_tokens'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests token replacement for Views tokens supplied by the Node module.
    */
diff --git a/core/modules/node/tests/src/Functional/Views/NodeIntegrationTest.php b/core/modules/node/tests/src/Functional/Views/NodeIntegrationTest.php
index 0f855d728b8268f88221d6a3d71076ce9b7893f9..965e2b3b92b4132a7738ce25252cd5b88cd0995b 100644
--- a/core/modules/node/tests/src/Functional/Views/NodeIntegrationTest.php
+++ b/core/modules/node/tests/src/Functional/Views/NodeIntegrationTest.php
@@ -16,6 +16,11 @@ class NodeIntegrationTest extends NodeTestBase {
    */
   public static $testViews = ['test_node_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests basic node view with a node type argument.
    */
diff --git a/core/modules/node/tests/src/Functional/Views/NodeLanguageTest.php b/core/modules/node/tests/src/Functional/Views/NodeLanguageTest.php
index 31e085213ceae054796ac1c6c1f41be4beff9507..012f6dd57cb3dee30c8da8bceec5e7d8e39582fd 100644
--- a/core/modules/node/tests/src/Functional/Views/NodeLanguageTest.php
+++ b/core/modules/node/tests/src/Functional/Views/NodeLanguageTest.php
@@ -21,6 +21,11 @@ class NodeLanguageTest extends NodeTestBase {
    */
   public static $modules = ['language', 'node_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/NodeRevisionWizardTest.php b/core/modules/node/tests/src/Functional/Views/NodeRevisionWizardTest.php
index 2dc97b00c33cb5c6ad5eec6b72f857cfbb35ea39..ba2a0c60a8f0926459cc66fe500ec250763ffd3c 100644
--- a/core/modules/node/tests/src/Functional/Views/NodeRevisionWizardTest.php
+++ b/core/modules/node/tests/src/Functional/Views/NodeRevisionWizardTest.php
@@ -13,6 +13,11 @@
  */
 class NodeRevisionWizardTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests creating a node revision view.
    */
diff --git a/core/modules/node/tests/src/Functional/Views/PathPluginTest.php b/core/modules/node/tests/src/Functional/Views/PathPluginTest.php
index b1da9fa4b56c2514669cc3352832da868945e715..ee9b2acf671e8a04f737c5aa03b6e8c4f434a7e1 100644
--- a/core/modules/node/tests/src/Functional/Views/PathPluginTest.php
+++ b/core/modules/node/tests/src/Functional/Views/PathPluginTest.php
@@ -18,6 +18,11 @@ class PathPluginTest extends NodeTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/RevisionLinkTest.php b/core/modules/node/tests/src/Functional/Views/RevisionLinkTest.php
index b5a4829b09fdc163835079fc60b18389a7da02d6..34f1f7f7fa044d35f143a13d8d23f629251262f1 100644
--- a/core/modules/node/tests/src/Functional/Views/RevisionLinkTest.php
+++ b/core/modules/node/tests/src/Functional/Views/RevisionLinkTest.php
@@ -20,6 +20,11 @@ class RevisionLinkTest extends NodeTestBase {
    */
   public static $testViews = ['test_node_revision_links'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests revision links.
    */
diff --git a/core/modules/node/tests/src/Functional/Views/RowPluginTest.php b/core/modules/node/tests/src/Functional/Views/RowPluginTest.php
index fdd4d45ad2097f6b41aaf92b72102a4e3a521f5e..a8627524d11649d9413cd777f431b73dada15b48 100644
--- a/core/modules/node/tests/src/Functional/Views/RowPluginTest.php
+++ b/core/modules/node/tests/src/Functional/Views/RowPluginTest.php
@@ -19,6 +19,11 @@ class RowPluginTest extends NodeTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/Functional/Views/StatusExtraTest.php b/core/modules/node/tests/src/Functional/Views/StatusExtraTest.php
index bce9046d6482d7d87997e90b9eb2821791fa831d..0347038d36fd5221603287b70ef78951632d1602 100644
--- a/core/modules/node/tests/src/Functional/Views/StatusExtraTest.php
+++ b/core/modules/node/tests/src/Functional/Views/StatusExtraTest.php
@@ -17,6 +17,11 @@ class StatusExtraTest extends NodeTestBase {
    */
   public static $modules = ['node_test_views', 'content_moderation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/node/tests/src/FunctionalJavascript/ContextualLinksTest.php b/core/modules/node/tests/src/FunctionalJavascript/ContextualLinksTest.php
index 7e9dae071b8e85e0144bae8853bc788e350f0dda..bf45eb6e1407c1005db614081df381f65e066c73 100644
--- a/core/modules/node/tests/src/FunctionalJavascript/ContextualLinksTest.php
+++ b/core/modules/node/tests/src/FunctionalJavascript/ContextualLinksTest.php
@@ -28,6 +28,11 @@ class ContextualLinksTest extends WebDriverTestBase {
    */
   protected static $modules = ['node', 'contextual'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/FunctionalJavascript/NodePreviewLinkTest.php b/core/modules/node/tests/src/FunctionalJavascript/NodePreviewLinkTest.php
index e1c185000f9539d2e72e2f461c3d7f605eade53a..ca2f81fe9599c231aa171efb2512907dd0271de8 100644
--- a/core/modules/node/tests/src/FunctionalJavascript/NodePreviewLinkTest.php
+++ b/core/modules/node/tests/src/FunctionalJavascript/NodePreviewLinkTest.php
@@ -17,6 +17,11 @@ class NodePreviewLinkTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'filter'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/node/tests/src/FunctionalJavascript/TestSettingSummariesContentType.php b/core/modules/node/tests/src/FunctionalJavascript/TestSettingSummariesContentType.php
index aef0c1e27d344bc94bf0b9b4e4cbc6c82a411e53..9aa6b8dc40479c6380b3e8b992a94970a1ee3966 100644
--- a/core/modules/node/tests/src/FunctionalJavascript/TestSettingSummariesContentType.php
+++ b/core/modules/node/tests/src/FunctionalJavascript/TestSettingSummariesContentType.php
@@ -11,6 +11,11 @@
  */
 class TestSettingSummariesContentType extends WebDriverTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/options/tests/src/Functional/OptionsDynamicValuesApiTest.php b/core/modules/options/tests/src/Functional/OptionsDynamicValuesApiTest.php
index 4f047f97f3b0e6d9b75260db33effb52a51bb0e6..a47bc1251fd9427cb505730b5e32814cbd09e453 100644
--- a/core/modules/options/tests/src/Functional/OptionsDynamicValuesApiTest.php
+++ b/core/modules/options/tests/src/Functional/OptionsDynamicValuesApiTest.php
@@ -9,6 +9,11 @@
 */
 class OptionsDynamicValuesApiTest extends OptionsDynamicValuesTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests options_allowed_values().
    *
diff --git a/core/modules/options/tests/src/Functional/OptionsDynamicValuesValidationTest.php b/core/modules/options/tests/src/Functional/OptionsDynamicValuesValidationTest.php
index 7ef535c96c165ea13e03290f5dda80583bd21d53..d44ec394115963b9a2019759b4fc670d9558baf8 100644
--- a/core/modules/options/tests/src/Functional/OptionsDynamicValuesValidationTest.php
+++ b/core/modules/options/tests/src/Functional/OptionsDynamicValuesValidationTest.php
@@ -9,6 +9,11 @@
  */
 class OptionsDynamicValuesValidationTest extends OptionsDynamicValuesTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test that allowed values function gets the entity.
    */
diff --git a/core/modules/options/tests/src/Functional/OptionsFieldUITest.php b/core/modules/options/tests/src/Functional/OptionsFieldUITest.php
index 7f42998767a0bbbfbc8990e9cca8085ac24d6c62..97e150407f8a2f3340d5df6b04e5b3c8c94ed0f1 100644
--- a/core/modules/options/tests/src/Functional/OptionsFieldUITest.php
+++ b/core/modules/options/tests/src/Functional/OptionsFieldUITest.php
@@ -21,6 +21,11 @@ class OptionsFieldUITest extends FieldTestBase {
    */
   public static $modules = ['node', 'options', 'field_test', 'taxonomy', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the created content type.
    *
diff --git a/core/modules/options/tests/src/Functional/OptionsFloatFieldImportTest.php b/core/modules/options/tests/src/Functional/OptionsFloatFieldImportTest.php
index d4d6afff9537688b7a9b565b55948468ee481929..556bc9ba2f32aac84ac07120dc31ed5870dea810 100644
--- a/core/modules/options/tests/src/Functional/OptionsFloatFieldImportTest.php
+++ b/core/modules/options/tests/src/Functional/OptionsFloatFieldImportTest.php
@@ -20,6 +20,11 @@ class OptionsFloatFieldImportTest extends FieldTestBase {
    */
   public static $modules = ['node', 'options', 'field_ui', 'config', 'options_config_install_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/options/tests/src/Functional/OptionsSelectDynamicValuesTest.php b/core/modules/options/tests/src/Functional/OptionsSelectDynamicValuesTest.php
index 0fb357be04b7d2d1ed1d7031c5e755d9199df6e0..02082cb1d680602f632d6e4abf284d382391d776 100644
--- a/core/modules/options/tests/src/Functional/OptionsSelectDynamicValuesTest.php
+++ b/core/modules/options/tests/src/Functional/OptionsSelectDynamicValuesTest.php
@@ -9,6 +9,11 @@
  */
 class OptionsSelectDynamicValuesTest extends OptionsDynamicValuesTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the 'options_select' widget (single select).
    */
diff --git a/core/modules/options/tests/src/Functional/OptionsWidgetsTest.php b/core/modules/options/tests/src/Functional/OptionsWidgetsTest.php
index b75aacaa7293808c9875d41160cde76407662267..ff48c684c2ed0c04b23a4c015bc25b40586854dd 100644
--- a/core/modules/options/tests/src/Functional/OptionsWidgetsTest.php
+++ b/core/modules/options/tests/src/Functional/OptionsWidgetsTest.php
@@ -21,6 +21,11 @@ class OptionsWidgetsTest extends FieldTestBase {
    */
   public static $modules = ['node', 'options', 'entity_test', 'options_test', 'taxonomy', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A field storage with cardinality 1 to use in this test class.
    *
diff --git a/core/modules/page_cache/tests/src/Functional/PageCacheTest.php b/core/modules/page_cache/tests/src/Functional/PageCacheTest.php
index 88c5311fddf3530ccc8be30f71d6bbcba3313450..553864e7b9c2edac26f97dea6fd3c315f934931b 100644
--- a/core/modules/page_cache/tests/src/Functional/PageCacheTest.php
+++ b/core/modules/page_cache/tests/src/Functional/PageCacheTest.php
@@ -29,6 +29,11 @@ class PageCacheTest extends BrowserTestBase {
    */
   public static $modules = ['test_page_test', 'system_test', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path/tests/src/Functional/PathAdminTest.php b/core/modules/path/tests/src/Functional/PathAdminTest.php
index 02a9762ffd02910afbe46f6d93654a734ba7c1e6..2ac11efa6a3dcf970a0c7011c797213867d7c77f 100644
--- a/core/modules/path/tests/src/Functional/PathAdminTest.php
+++ b/core/modules/path/tests/src/Functional/PathAdminTest.php
@@ -16,6 +16,11 @@ class PathAdminTest extends PathTestBase {
    */
   public static $modules = ['path'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/path/tests/src/Functional/PathAliasTest.php b/core/modules/path/tests/src/Functional/PathAliasTest.php
index 295430480cd5df67328c28cabcba63c0372b8af0..4cf25f6d625adbe3dd72a8a3a32b340e00d8885e 100644
--- a/core/modules/path/tests/src/Functional/PathAliasTest.php
+++ b/core/modules/path/tests/src/Functional/PathAliasTest.php
@@ -21,6 +21,11 @@ class PathAliasTest extends PathTestBase {
    */
   public static $modules = ['path'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/path/tests/src/Functional/PathContentModerationTest.php b/core/modules/path/tests/src/Functional/PathContentModerationTest.php
index b69a5dbe5b5dd95a32efb9e58356c08274ba8214..cae1928bb825ba5241d54cdc7c30dbcc5701de41 100644
--- a/core/modules/path/tests/src/Functional/PathContentModerationTest.php
+++ b/core/modules/path/tests/src/Functional/PathContentModerationTest.php
@@ -28,6 +28,11 @@ class PathContentModerationTest extends BrowserTestBase {
     'content_translation',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path/tests/src/Functional/PathLanguageTest.php b/core/modules/path/tests/src/Functional/PathLanguageTest.php
index ddb512fd799be22df55291e8e10ad0c5683874ae..18a51749e441a594477daee99f590bcc8a910f5a 100644
--- a/core/modules/path/tests/src/Functional/PathLanguageTest.php
+++ b/core/modules/path/tests/src/Functional/PathLanguageTest.php
@@ -16,6 +16,11 @@ class PathLanguageTest extends PathTestBase {
    */
   public static $modules = ['path', 'locale', 'locale_test', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An user with permissions to administer content types.
    *
diff --git a/core/modules/path/tests/src/Functional/PathLanguageUiTest.php b/core/modules/path/tests/src/Functional/PathLanguageUiTest.php
index b2dc2b0759c9e8497468ea8b4c541415bca5a774..6ab6e2c22ca64214111e141f5ddd2cda0ef059f0 100644
--- a/core/modules/path/tests/src/Functional/PathLanguageUiTest.php
+++ b/core/modules/path/tests/src/Functional/PathLanguageUiTest.php
@@ -18,6 +18,11 @@ class PathLanguageUiTest extends PathTestBase {
    */
   public static $modules = ['path', 'locale', 'locale_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/path/tests/src/Functional/PathMediaFormTest.php b/core/modules/path/tests/src/Functional/PathMediaFormTest.php
index 7fd3a745bef9f1029f2d242fd8da83feacf650ac..9f34cd85a71149a932c5e4af431ceff74fe6fff8 100644
--- a/core/modules/path/tests/src/Functional/PathMediaFormTest.php
+++ b/core/modules/path/tests/src/Functional/PathMediaFormTest.php
@@ -16,6 +16,11 @@ class PathMediaFormTest extends PathTestBase {
    */
   public static $modules = ['media', 'media_test_source'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path/tests/src/Functional/PathNodeFormTest.php b/core/modules/path/tests/src/Functional/PathNodeFormTest.php
index 9070cc75309846da67b6fb86593effe083682388..66c6198cc925175a1f6b2e14ae6e0ba09b140ae6 100644
--- a/core/modules/path/tests/src/Functional/PathNodeFormTest.php
+++ b/core/modules/path/tests/src/Functional/PathNodeFormTest.php
@@ -16,6 +16,11 @@ class PathNodeFormTest extends PathTestBase {
    */
   public static $modules = ['node', 'path'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/path/tests/src/Functional/PathTaxonomyTermTest.php b/core/modules/path/tests/src/Functional/PathTaxonomyTermTest.php
index ebf3205ae7ae85ca5a60a231d0e89d6d1b56bdcb..1db6bb1885d782e0d16c20551eea0c419dd9433a 100644
--- a/core/modules/path/tests/src/Functional/PathTaxonomyTermTest.php
+++ b/core/modules/path/tests/src/Functional/PathTaxonomyTermTest.php
@@ -19,6 +19,11 @@ class PathTaxonomyTermTest extends PathTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonAnonTest.php b/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonAnonTest.php
index 22e3f441af254dfce37ddd7c92ad6358e2e0c15c..60917af353cfd8db85a9686b4eba9dfa46012582 100644
--- a/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonAnonTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class PathAliasHalJsonAnonTest extends PathAliasHalJsonTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonBasicAuthTest.php b/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonBasicAuthTest.php
index 634c78970bf010ae9335da3ae22b6c66c6cb66a3..3007a157e0deda91fe1a7f2edb29d333a0e107e5 100644
--- a/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonBasicAuthTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class PathAliasHalJsonBasicAuthTest extends PathAliasHalJsonTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonCookieTest.php b/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonCookieTest.php
index 746daaeb4b40c0b966cadb0d2caaa251bd7bafa5..62f39885a364f2772bb6bc748395f83c3cdd760c 100644
--- a/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonCookieTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Hal/PathAliasHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class PathAliasHalJsonCookieTest extends PathAliasHalJsonTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonAnonTest.php b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonAnonTest.php
index 8a5c3a79f91aabd6850a8a2dd91f881710a3045a..1e1b4aa214011b58f13f5501b9b1ee1de9d5dbcc 100644
--- a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonAnonTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonAnonTest.php
@@ -23,4 +23,9 @@ class PathAliasJsonAnonTest extends PathAliasResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonBasicAuthTest.php b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonBasicAuthTest.php
index b00359e0cd8f0b2070d7c47828c2f206460412b4..17cd95e8961f1ad09404e091e71b9c5a4c106c4a 100644
--- a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonBasicAuthTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonBasicAuthTest.php
@@ -18,6 +18,11 @@ class PathAliasJsonBasicAuthTest extends PathAliasResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonCookieTest.php b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonCookieTest.php
index a93723d72f30845b1d97539bcb8d9d0a71ef3093..f620781ed0ad0fc2789534ca4198f3130e82c632 100644
--- a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonCookieTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasJsonCookieTest.php
@@ -28,4 +28,9 @@ class PathAliasJsonCookieTest extends PathAliasResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlAnonTest.php b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlAnonTest.php
index 0ab6712f1d651f5f11001a44325ce7c7b6ca0a7e..a987e0dba61d8e35809d5802017447e5f4f24efe 100644
--- a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlAnonTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlAnonTest.php
@@ -25,4 +25,9 @@ class PathAliasXmlAnonTest extends PathAliasResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlBasicAuthTest.php b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlBasicAuthTest.php
index 677b5f4d2541692916c999d110acf6535c84e5a5..eda55d9f03292da15773fdceed440099bbaf6e7b 100644
--- a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlBasicAuthTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlBasicAuthTest.php
@@ -20,6 +20,11 @@ class PathAliasXmlBasicAuthTest extends PathAliasResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlCookieTest.php b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlCookieTest.php
index c5fea144785e2d0aaecbed50edaa6036f1a254e1..e3695cef3221d938b567ac438e507943018e126b 100644
--- a/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlCookieTest.php
+++ b/core/modules/path_alias/tests/src/Functional/Rest/PathAliasXmlCookieTest.php
@@ -30,4 +30,9 @@ class PathAliasXmlCookieTest extends PathAliasResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php b/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php
index 58d7079987aedf216f3b4f5523a3a9aed77c8307..800c8e86c980d4d85a49dfba93a2f967739def1a 100644
--- a/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php
+++ b/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php
@@ -25,6 +25,11 @@ class UrlAlterFunctionalTest extends BrowserTestBase {
    */
   public static $modules = ['path', 'forum', 'url_alter_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test that URL altering works and that it occurs in the correct order.
    */
diff --git a/core/modules/quickedit/tests/src/Functional/QuickEditCustomPipelineTest.php b/core/modules/quickedit/tests/src/Functional/QuickEditCustomPipelineTest.php
index 8921a9cf6590c3dfcb8cf200dbe5af800bb6f6e6..bde1252427fe6556c6133b3d7577bcbd5bd5bdff 100644
--- a/core/modules/quickedit/tests/src/Functional/QuickEditCustomPipelineTest.php
+++ b/core/modules/quickedit/tests/src/Functional/QuickEditCustomPipelineTest.php
@@ -22,6 +22,11 @@ class QuickEditCustomPipelineTest extends BrowserTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that Quick Edit works with custom render pipelines.
    */
diff --git a/core/modules/quickedit/tests/src/Functional/QuickEditEndPointAccessTest.php b/core/modules/quickedit/tests/src/Functional/QuickEditEndPointAccessTest.php
index 8d30a9c94dd0320d269590b9a8641ef021826e5d..461b0a7a1af14236f72c1512fd8376d48eee63aa 100644
--- a/core/modules/quickedit/tests/src/Functional/QuickEditEndPointAccessTest.php
+++ b/core/modules/quickedit/tests/src/Functional/QuickEditEndPointAccessTest.php
@@ -22,6 +22,11 @@ class QuickEditEndPointAccessTest extends BrowserTestBase {
     'node',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/quickedit/tests/src/Functional/QuickEditMinimalTest.php b/core/modules/quickedit/tests/src/Functional/QuickEditMinimalTest.php
index b61dc5ab78cad07f6bbb1692ffb30a6e3e069ba0..2242e97a2611243d07384f8800b9ee7290d41bc5 100644
--- a/core/modules/quickedit/tests/src/Functional/QuickEditMinimalTest.php
+++ b/core/modules/quickedit/tests/src/Functional/QuickEditMinimalTest.php
@@ -24,6 +24,11 @@ class QuickEditMinimalTest extends BrowserTestBase {
     'quickedit_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that Quick Edit works with no admin theme.
    *
diff --git a/core/modules/quickedit/tests/src/FunctionalJavascript/FieldTest.php b/core/modules/quickedit/tests/src/FunctionalJavascript/FieldTest.php
index 56d303d659de53a697443709b33c234b3b85cf1a..0b6505bd40db6ae94cf8e54e1af4d21469b7f9ce 100644
--- a/core/modules/quickedit/tests/src/FunctionalJavascript/FieldTest.php
+++ b/core/modules/quickedit/tests/src/FunctionalJavascript/FieldTest.php
@@ -28,6 +28,11 @@ class FieldTest extends WebDriverTestBase {
     'quickedit',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditAutocompleteTermTest.php b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditAutocompleteTermTest.php
index d58f0e7bb5d98a6d3fbd4254e6f05856663f064e..f08ea2d46b1fd10e3f84fe6e75049f57c567136d 100644
--- a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditAutocompleteTermTest.php
+++ b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditAutocompleteTermTest.php
@@ -31,6 +31,11 @@ class QuickEditAutocompleteTermTest extends WebDriverTestBase {
     'ckeditor',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Stores the node used for the tests.
    *
diff --git a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditFileTest.php b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditFileTest.php
index a1de95c01bf78f626941296b4ea5760589101f09..f21ba6d7ab5471f432428ed2b748901cae4b05dc 100644
--- a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditFileTest.php
+++ b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditFileTest.php
@@ -23,6 +23,11 @@ class QuickEditFileTest extends QuickEditJavascriptTestBase {
     'file',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php
index 52d645f0f8c1f77bfdd86f3a28f33cba070ea325..24f36d440ecae5c8dc5bdf4454edbeef3a581113 100644
--- a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php
+++ b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php
@@ -31,6 +31,11 @@ class QuickEditIntegrationTest extends QuickEditJavascriptTestBase {
     'hold_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with permissions to edit Articles and use Quick Edit.
    *
diff --git a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditLoadingTest.php b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditLoadingTest.php
index 2424374570bd6468553b2ccc6879dbf5fcfeba4d..4f52c00efa41ce7ececd452ed986fc3b6acf2d6f 100644
--- a/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditLoadingTest.php
+++ b/core/modules/quickedit/tests/src/FunctionalJavascript/QuickEditLoadingTest.php
@@ -41,6 +41,11 @@ class QuickEditLoadingTest extends WebDriverTestBase {
     'image',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * An user with permissions to create and edit articles.
    *
diff --git a/core/modules/rdf/tests/src/Functional/CommentAttributesTest.php b/core/modules/rdf/tests/src/Functional/CommentAttributesTest.php
index 6daec72fdc9af70ce8ac8f28aa974ac9216475d7..2be1e85cc226c00ac62c4ced53bd42da2a5d5a6b 100644
--- a/core/modules/rdf/tests/src/Functional/CommentAttributesTest.php
+++ b/core/modules/rdf/tests/src/Functional/CommentAttributesTest.php
@@ -23,6 +23,11 @@ class CommentAttributesTest extends CommentTestBase {
    */
   public static $modules = ['views', 'node', 'comment', 'rdf'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * URI of the front page of the Drupal site.
    *
diff --git a/core/modules/rdf/tests/src/Functional/EntityReferenceFieldAttributesTest.php b/core/modules/rdf/tests/src/Functional/EntityReferenceFieldAttributesTest.php
index 23468c4fcc632bbc96d72640a0365ad815c5b4d0..8c577c1e12bfcbce494af3661cc5e0551b2b2448 100644
--- a/core/modules/rdf/tests/src/Functional/EntityReferenceFieldAttributesTest.php
+++ b/core/modules/rdf/tests/src/Functional/EntityReferenceFieldAttributesTest.php
@@ -20,6 +20,11 @@ class EntityReferenceFieldAttributesTest extends TaxonomyTestBase {
    */
   public static $modules = ['rdf', 'field_test', 'file', 'image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the taxonomy term reference field used in the test.
    *
diff --git a/core/modules/rdf/tests/src/Functional/FileFieldAttributesTest.php b/core/modules/rdf/tests/src/Functional/FileFieldAttributesTest.php
index f756c9e28db0e2335089a833b7ce9d3ec58869c8..fb8eb96c7e09ee58049b7cf61e11f1c120d151e0 100644
--- a/core/modules/rdf/tests/src/Functional/FileFieldAttributesTest.php
+++ b/core/modules/rdf/tests/src/Functional/FileFieldAttributesTest.php
@@ -20,6 +20,11 @@ class FileFieldAttributesTest extends FileFieldTestBase {
    */
   public static $modules = ['rdf', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the file field used in the test.
    *
diff --git a/core/modules/rdf/tests/src/Functional/GetRdfNamespacesTest.php b/core/modules/rdf/tests/src/Functional/GetRdfNamespacesTest.php
index 0b162a4a905556f5b485e4c12af43f0624635960..aade6bc622a687ecb635b90b9878239823e949cb 100644
--- a/core/modules/rdf/tests/src/Functional/GetRdfNamespacesTest.php
+++ b/core/modules/rdf/tests/src/Functional/GetRdfNamespacesTest.php
@@ -18,6 +18,11 @@ class GetRdfNamespacesTest extends BrowserTestBase {
    */
   public static $modules = ['rdf', 'rdf_test_namespaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests getting RDF namespaces.
    */
diff --git a/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonAnonTest.php b/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonAnonTest.php
index 2d241e99677a33d48f33a16f679c86b4fee96988..17917981a2702633e1af37ad41ecc01fb8666d52 100644
--- a/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonAnonTest.php
+++ b/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class RdfMappingHalJsonAnonTest extends RdfMappingResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonBasicAuthTest.php b/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonBasicAuthTest.php
index 346ad229e0266091cc7f108e685b2b6bae6e5f7b..3c9969900a86e568b7b5ad2667be152eed2487e6 100644
--- a/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonBasicAuthTest.php
+++ b/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class RdfMappingHalJsonBasicAuthTest extends RdfMappingResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonCookieTest.php b/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonCookieTest.php
index ff90d902a1dfb07832f44b75f23d3314112a07fa..8c5c47c0fd038e97ab668b0fc1a4f7c5fe2ce3e1 100644
--- a/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonCookieTest.php
+++ b/core/modules/rdf/tests/src/Functional/Hal/RdfMappingHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class RdfMappingHalJsonCookieTest extends RdfMappingResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rdf/tests/src/Functional/ImageFieldAttributesTest.php b/core/modules/rdf/tests/src/Functional/ImageFieldAttributesTest.php
index 9c66230e8009864d4ccd61f5bf5da040e0f29415..bd7eab7d7e37b5773a80b421987802e8f2949eee 100644
--- a/core/modules/rdf/tests/src/Functional/ImageFieldAttributesTest.php
+++ b/core/modules/rdf/tests/src/Functional/ImageFieldAttributesTest.php
@@ -27,6 +27,11 @@ class ImageFieldAttributesTest extends ImageFieldTestBase {
    */
   public static $modules = ['rdf', 'image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The name of the image field used in the test.
    *
diff --git a/core/modules/rdf/tests/src/Functional/NodeAttributesTest.php b/core/modules/rdf/tests/src/Functional/NodeAttributesTest.php
index 7811b976b0901771a9a4f47ede4a249b97016063..00a4a405c4855b92381f110ae4af4786e5ade996 100644
--- a/core/modules/rdf/tests/src/Functional/NodeAttributesTest.php
+++ b/core/modules/rdf/tests/src/Functional/NodeAttributesTest.php
@@ -19,6 +19,11 @@ class NodeAttributesTest extends NodeTestBase {
    */
   public static $modules = ['rdf'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonAnonTest.php b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonAnonTest.php
index bb53cc7622590f44c2c6c6b21082f6eae8ad068e..faed795066f14db6669ac87d37e0d415f8c0502f 100644
--- a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonAnonTest.php
+++ b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonAnonTest.php
@@ -21,4 +21,9 @@ class RdfMappingJsonAnonTest extends RdfMappingResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonBasicAuthTest.php b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonBasicAuthTest.php
index 9537336780fd2be0f17d616349a3b35067dfa185..7727fedfaf25d17625a2be3d3ec7f747e1f68d90 100644
--- a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonBasicAuthTest.php
+++ b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class RdfMappingJsonBasicAuthTest extends RdfMappingResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonCookieTest.php b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonCookieTest.php
index 392d45e9b1aef1a83feb8072a5102e00057f72ef..768aab6b9dfa335f7142edfb8a64038cd9a80868 100644
--- a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonCookieTest.php
+++ b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingJsonCookieTest.php
@@ -26,4 +26,9 @@ class RdfMappingJsonCookieTest extends RdfMappingResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlAnonTest.php b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlAnonTest.php
index ab6922b8e7aa4a53a025cd7da96d0e2ba3eee978..a1970f6bd5f7197ac8f35271857a9f0404a26716 100644
--- a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlAnonTest.php
+++ b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlAnonTest.php
@@ -23,4 +23,9 @@ class RdfMappingXmlAnonTest extends RdfMappingResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlBasicAuthTest.php b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlBasicAuthTest.php
index 9cf6b97d51775591b1d7e4db787e13a3314a4e11..d7a8c1918dc1b3ea82a3663a7ce5d266adeb7fb0 100644
--- a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlBasicAuthTest.php
+++ b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class RdfMappingXmlBasicAuthTest extends RdfMappingResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlCookieTest.php b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlCookieTest.php
index 1519e5ac725b6851ebbb0875bca2e8c173c71f64..c84fdc0755556627545ec00dbaeb5f3692382462 100644
--- a/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlCookieTest.php
+++ b/core/modules/rdf/tests/src/Functional/Rest/RdfMappingXmlCookieTest.php
@@ -28,4 +28,9 @@ class RdfMappingXmlCookieTest extends RdfMappingResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rdf/tests/src/Functional/StandardProfileTest.php b/core/modules/rdf/tests/src/Functional/StandardProfileTest.php
index a137fb8a8acccd381fe06d2baad3a82f8bf04c5e..93d78a93a4bf4a0559870f3fced135e301f600dc 100644
--- a/core/modules/rdf/tests/src/Functional/StandardProfileTest.php
+++ b/core/modules/rdf/tests/src/Functional/StandardProfileTest.php
@@ -18,6 +18,11 @@
  */
 class StandardProfileTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The profile used during tests.
    *
@@ -105,10 +110,6 @@ class StandardProfileTest extends BrowserTestBase {
   protected function setUp() {
     parent::setUp();
 
-    // Use Classy theme for testing markup output.
-    \Drupal::service('theme_installer')->install(['classy']);
-    $this->config('system.theme')->set('default', 'classy')->save();
-
     $this->baseUri = Url::fromRoute('<front>', [], ['absolute' => TRUE])->toString();
 
     // Create two test users.
diff --git a/core/modules/rdf/tests/src/Functional/TaxonomyAttributesTest.php b/core/modules/rdf/tests/src/Functional/TaxonomyAttributesTest.php
index 7b0720dfad72a1e534a77d814a283e9b631c6ec8..529c99b35a3c22e85de8b51779d401930f32530f 100644
--- a/core/modules/rdf/tests/src/Functional/TaxonomyAttributesTest.php
+++ b/core/modules/rdf/tests/src/Functional/TaxonomyAttributesTest.php
@@ -19,6 +19,11 @@ class TaxonomyAttributesTest extends TaxonomyTestBase {
    */
   public static $modules = ['rdf', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Vocabulary created for testing purposes.
    *
diff --git a/core/modules/rdf/tests/src/Functional/UserAttributesTest.php b/core/modules/rdf/tests/src/Functional/UserAttributesTest.php
index 0373e1b49b07cbb20679592f79741eb1f67a6fa0..4a38c57f9d076dce2fa03ce06eae1da15e5967db 100644
--- a/core/modules/rdf/tests/src/Functional/UserAttributesTest.php
+++ b/core/modules/rdf/tests/src/Functional/UserAttributesTest.php
@@ -19,6 +19,11 @@ class UserAttributesTest extends BrowserTestBase {
    */
   public static $modules = ['rdf', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     rdf_get_mapping('user', 'user')
diff --git a/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonAnonTest.php b/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonAnonTest.php
index 50dc1970dfa920e543b5287cff6a8b27f6a8a2ef..cff45272e3840e944235a1f2ff3724314b432f22 100644
--- a/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonAnonTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ResponsiveImageStyleHalJsonAnonTest extends ResponsiveImageStyleResourceTe
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonBasicAuthTest.php b/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonBasicAuthTest.php
index 1f45a2d74367887a625775fd4df584ad632779a9..17e896ee20bcdd26bf4481dc14fad850405d7862 100644
--- a/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonBasicAuthTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonBasicAuthTest.php
@@ -22,6 +22,11 @@ class ResponsiveImageStyleHalJsonBasicAuthTest extends ResponsiveImageStyleResou
    */
   protected static $format = 'hal_json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonCookieTest.php b/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonCookieTest.php
index 85d95431f58d5efb31b63632dfb0de0431c0e1fe..3d32819dbc1531a039e0575b4deab32d8b9a9529 100644
--- a/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonCookieTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Hal/ResponsiveImageStyleHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ResponsiveImageStyleHalJsonCookieTest extends ResponsiveImageStyleResource
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/responsive_image/tests/src/Functional/ResponsiveImageAdminUITest.php b/core/modules/responsive_image/tests/src/Functional/ResponsiveImageAdminUITest.php
index 8dc5e24d3a4183f01fffd8309c05a5eec54d0cf4..72de87c886f5cd4f18474bba5e6a4bd450966635 100644
--- a/core/modules/responsive_image/tests/src/Functional/ResponsiveImageAdminUITest.php
+++ b/core/modules/responsive_image/tests/src/Functional/ResponsiveImageAdminUITest.php
@@ -19,6 +19,11 @@ class ResponsiveImageAdminUITest extends BrowserTestBase {
    */
   public static $modules = ['responsive_image', 'responsive_image_test_module'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Drupal\simpletest\WebTestBase\setUp().
    */
diff --git a/core/modules/responsive_image/tests/src/Functional/ResponsiveImageFieldDisplayTest.php b/core/modules/responsive_image/tests/src/Functional/ResponsiveImageFieldDisplayTest.php
index ae9f7be86dd890d0e160a161a752dcb0a4acf8b3..9b805d6e625f7124b2c41d36765d1faf7c07092f 100644
--- a/core/modules/responsive_image/tests/src/Functional/ResponsiveImageFieldDisplayTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/ResponsiveImageFieldDisplayTest.php
@@ -21,6 +21,11 @@ class ResponsiveImageFieldDisplayTest extends ImageFieldTestBase {
 
   use TestFileCreationTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $dumpHeaders = TRUE;
 
   /**
diff --git a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonAnonTest.php b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonAnonTest.php
index 42b3098dd5a621bc78c8ecba88d9238d71837e4b..2b35fd2b5704e11b05e30edac9e2916aaad04b0c 100644
--- a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonAnonTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonAnonTest.php
@@ -21,4 +21,9 @@ class ResponsiveImageStyleJsonAnonTest extends ResponsiveImageStyleResourceTestB
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonBasicAuthTest.php b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonBasicAuthTest.php
index b3c9127da412590ca0b3062856cd61ac694ba0de..76eadc341eec797c013c8c4eac8993a06cce24cd 100644
--- a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonBasicAuthTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ResponsiveImageStyleJsonBasicAuthTest extends ResponsiveImageStyleResource
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonCookieTest.php b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonCookieTest.php
index e89122eab66d4488d2770217edc2081de2d87cd4..4e78c8aa31f85530db35dc56084a7336d8b588ef 100644
--- a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonCookieTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleJsonCookieTest.php
@@ -26,4 +26,9 @@ class ResponsiveImageStyleJsonCookieTest extends ResponsiveImageStyleResourceTes
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlAnonTest.php b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlAnonTest.php
index 8493eddabee842df9742d87311f5f90bb6b3730d..b07b2b06b5d775e110d33c211ddee63d11b3aedc 100644
--- a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlAnonTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlAnonTest.php
@@ -23,4 +23,9 @@ class ResponsiveImageStyleXmlAnonTest extends ResponsiveImageStyleResourceTestBa
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlBasicAuthTest.php b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlBasicAuthTest.php
index e850e99d57bae7635fcb60b5bbbd4d0a96b0d520..75b6ead6be61d53beebfd558a8814c29a885e979 100644
--- a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlBasicAuthTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ResponsiveImageStyleXmlBasicAuthTest extends ResponsiveImageStyleResourceT
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlCookieTest.php b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlCookieTest.php
index f63f91cd5425a8e9e91b55d15f04f07cc4a6dc5e..f71632b757d130d507f32870cdb2a99b3acd0477 100644
--- a/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlCookieTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/Rest/ResponsiveImageStyleXmlCookieTest.php
@@ -28,4 +28,9 @@ class ResponsiveImageStyleXmlCookieTest extends ResponsiveImageStyleResourceTest
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/responsive_image/tests/src/Functional/ViewsIntegrationTest.php b/core/modules/responsive_image/tests/src/Functional/ViewsIntegrationTest.php
index 33f19a5be56412f0b05fea22fbd9c9926f7bc296..4a926dffdf6d73686bdf24cc0ea27e0d90ce3d0c 100644
--- a/core/modules/responsive_image/tests/src/Functional/ViewsIntegrationTest.php
+++ b/core/modules/responsive_image/tests/src/Functional/ViewsIntegrationTest.php
@@ -34,6 +34,11 @@ class ViewsIntegrationTest extends ViewTestBase {
     'responsive_image_test_module',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The test views to enable.
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceRestTestCoverageTest.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceRestTestCoverageTest.php
index 82d47b95a7f5d20241fdeb9b4f0c4fe565dbe1ab..8be771f31c265601a37508bbbd9f91917f767561 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceRestTestCoverageTest.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceRestTestCoverageTest.php
@@ -23,6 +23,11 @@ class EntityResourceRestTestCoverageTest extends BrowserTestBase {
    */
   protected $definitions;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonAnonTest.php b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonAnonTest.php
index f28788ac80183f80a8cbb6a17af4ba455ed9cebc..c5b18daa94b1cacee0b6258ef953b7c68bf4b8fe 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonAnonTest.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonAnonTest.php
@@ -21,4 +21,9 @@ class ModeratedNodeJsonAnonTest extends ModeratedNodeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonBasicAuthTest.php b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonBasicAuthTest.php
index b47a86f65ffb959b7f4ddf59c85c967400af38c2..e1051e94144bb6ad79d26c1f7dd6b2faffd56bee 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonBasicAuthTest.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ModeratedNodeJsonBasicAuthTest extends ModeratedNodeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonCookieTest.php b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonCookieTest.php
index 08fc4b5f4fb087427a297d08b04caebf6a4bef3e..ffcb5e0947673b4a65047d287f264a5f5d37c85e 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonCookieTest.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeJsonCookieTest.php
@@ -26,4 +26,9 @@ class ModeratedNodeJsonCookieTest extends ModeratedNodeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlAnonTest.php b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlAnonTest.php
index 4b91d766c6f4c977246650bdea498b708c396401..3cc3853df1be3535d82d0b032c25bb377d6d9be8 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlAnonTest.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlAnonTest.php
@@ -23,6 +23,11 @@ class ModeratedNodeXmlAnonTest extends ModeratedNodeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlBasicAuthTest.php b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlBasicAuthTest.php
index a321e03cb25f0227081f4fcc38c38897ac0869d0..9977177b7cd4744582592f97a8ae424b24a269d6 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlBasicAuthTest.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ModeratedNodeXmlBasicAuthTest extends ModeratedNodeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlCookieTest.php b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlCookieTest.php
index 2014a56ff43d407e00eaca5778a80db192304d5e..8a2193fb90dbdd3fd714a73c40b3578021c42940 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlCookieTest.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/ModeratedNode/ModeratedNodeXmlCookieTest.php
@@ -28,6 +28,11 @@ class ModeratedNodeXmlCookieTest extends ModeratedNodeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonAnonTest.php b/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonAnonTest.php
index 72ccd45e932a8f9f1d67d1abf8111a2709af5ea1..7731048a858c251322476eae7d91904ad424aea4 100644
--- a/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonAnonTest.php
+++ b/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class RestResourceConfigHalJsonAnonTest extends RestResourceConfigResourceTestBa
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonBasicAuthTest.php b/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonBasicAuthTest.php
index e5e9a7efbbff9a01793dabb52c7384c373080186..e220693e9f5c8253b8203ebaca17a213061092ea 100644
--- a/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonBasicAuthTest.php
+++ b/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class RestResourceConfigHalJsonBasicAuthTest extends RestResourceConfigResourceT
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonCookieTest.php b/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonCookieTest.php
index 606d3fd641327aaf8d75e7f6f592d5c950f8de23..d224369f6af8dc010a98c9406fcf65c8e961985c 100644
--- a/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonCookieTest.php
+++ b/core/modules/rest/tests/src/Functional/Hal/RestResourceConfigHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class RestResourceConfigHalJsonCookieTest extends RestResourceConfigResourceTest
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/ResourceTest.php b/core/modules/rest/tests/src/Functional/ResourceTest.php
index 5a569106910d1e0371323082a7143f741b22cb6d..57a6840bff315491f657dfa61f173fe199b7bee4 100644
--- a/core/modules/rest/tests/src/Functional/ResourceTest.php
+++ b/core/modules/rest/tests/src/Functional/ResourceTest.php
@@ -25,6 +25,11 @@ class ResourceTest extends BrowserTestBase {
    */
   public static $modules = ['hal', 'rest', 'entity_test', 'rest_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The entity.
    *
diff --git a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonAnonTest.php b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonAnonTest.php
index ce355909d11ef53afca525b428237ed63643752b..0caad8c819229bd4b3859e64d177526ab9a1a63e 100644
--- a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonAnonTest.php
+++ b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonAnonTest.php
@@ -21,4 +21,9 @@ class RestResourceConfigJsonAnonTest extends RestResourceConfigResourceTestBase
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonBasicAuthTest.php b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonBasicAuthTest.php
index 8ac84636ec3145918177148b8c7a9b5db913d179..7a1f9c0a5848a5d94c7656d788e499bf5771501d 100644
--- a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonBasicAuthTest.php
+++ b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class RestResourceConfigJsonBasicAuthTest extends RestResourceConfigResourceTest
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonCookieTest.php b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonCookieTest.php
index 4971f59a44eb817e63e870e4ca1793666ddbea17..0fee7a1c4f69a6449e16a264744275faa64a33a4 100644
--- a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonCookieTest.php
+++ b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigJsonCookieTest.php
@@ -26,4 +26,9 @@ class RestResourceConfigJsonCookieTest extends RestResourceConfigResourceTestBas
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlAnonTest.php b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlAnonTest.php
index a508b55409d7015ad943f5b82704764a6c1a3dd2..5c0c24e47a7d979255863f9ff9a21cfc903b7b9f 100644
--- a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlAnonTest.php
+++ b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlAnonTest.php
@@ -23,4 +23,9 @@ class RestResourceConfigXmlAnonTest extends RestResourceConfigResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlBasicAuthTest.php b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlBasicAuthTest.php
index c5034b4ee5cc04e708c00613a630bc40ff295868..df9e46e251ce255da64dd1665498897baa1ab18a 100644
--- a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlBasicAuthTest.php
+++ b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class RestResourceConfigXmlBasicAuthTest extends RestResourceConfigResourceTestB
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlCookieTest.php b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlCookieTest.php
index 377a4497e971068b9b9645edea4b65b2ffd96f93..796d5424f848abc2b8edc0ef5bbb583130e5cbcd 100644
--- a/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlCookieTest.php
+++ b/core/modules/rest/tests/src/Functional/Rest/RestResourceConfigXmlCookieTest.php
@@ -28,4 +28,9 @@ class RestResourceConfigXmlCookieTest extends RestResourceConfigResourceTestBase
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/rest/tests/src/Functional/Views/ExcludedFieldTokenTest.php b/core/modules/rest/tests/src/Functional/Views/ExcludedFieldTokenTest.php
index cf9913d85a43514c9048b1091bb8fd6766d36f79..22d583fde6b99e420bf97279666a784f0dea9f50 100644
--- a/core/modules/rest/tests/src/Functional/Views/ExcludedFieldTokenTest.php
+++ b/core/modules/rest/tests/src/Functional/Views/ExcludedFieldTokenTest.php
@@ -28,6 +28,11 @@ class ExcludedFieldTokenTest extends ViewTestBase {
    */
   public static $testViews = ['test_excluded_field_token_display'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The modules that need to be installed for this test.
    *
diff --git a/core/modules/rest/tests/src/Functional/Views/FieldCounterTest.php b/core/modules/rest/tests/src/Functional/Views/FieldCounterTest.php
index 8d3e4f755041cc992041ffd0b192e583e8a1ab6e..ef8d0a034b2c6f7ef64b3da5c75a3da34c6857ec 100644
--- a/core/modules/rest/tests/src/Functional/Views/FieldCounterTest.php
+++ b/core/modules/rest/tests/src/Functional/Views/FieldCounterTest.php
@@ -28,6 +28,11 @@ class FieldCounterTest extends ViewTestBase {
    */
   public static $testViews = ['test_field_counter_display'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The modules that need to be installed for this test.
    *
diff --git a/core/modules/rest/tests/src/Functional/Views/RestExportAuthTest.php b/core/modules/rest/tests/src/Functional/Views/RestExportAuthTest.php
index 24546089cd5442a870cf021dd6d40708201a5ad6..4b692260114c6d38aef61d27b68d23bf43a40cf0 100644
--- a/core/modules/rest/tests/src/Functional/Views/RestExportAuthTest.php
+++ b/core/modules/rest/tests/src/Functional/Views/RestExportAuthTest.php
@@ -17,6 +17,11 @@ class RestExportAuthTest extends ViewTestBase {
    */
   public static $modules = ['rest', 'views_ui', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/rest/tests/src/Functional/Views/StyleSerializerTest.php b/core/modules/rest/tests/src/Functional/Views/StyleSerializerTest.php
index e307c77bc48f5235593f32c92d99c798bfb54716..c0de5c8578da66c3d2a8f3f35e27fcceaa8ba87a 100644
--- a/core/modules/rest/tests/src/Functional/Views/StyleSerializerTest.php
+++ b/core/modules/rest/tests/src/Functional/Views/StyleSerializerTest.php
@@ -38,6 +38,11 @@ class StyleSerializerTest extends ViewTestBase {
    */
   public static $modules = ['views_ui', 'entity_test', 'hal', 'rest_test_views', 'node', 'text', 'field', 'language', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonAnonTest.php b/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonAnonTest.php
index cd0079803ce7b09fedbc618e4256f3a3d405cda3..833c59beed1bf5c743cc3b417c034af64fe1cc0c 100644
--- a/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonAnonTest.php
+++ b/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class SearchPageHalJsonAnonTest extends SearchPageResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonBasicAuthTest.php b/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonBasicAuthTest.php
index d1ff293ba369ebf5f1f0a4be2abe9ed0383fa09a..d7e8a619bffec39f04739c81279648aa01f87f77 100644
--- a/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonBasicAuthTest.php
+++ b/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class SearchPageHalJsonBasicAuthTest extends SearchPageResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonCookieTest.php b/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonCookieTest.php
index a09fa5f9b12396d769ae458337d742b034dd89d8..47ab4dd46b740aedee963d70bd875218c9c0cdfa 100644
--- a/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonCookieTest.php
+++ b/core/modules/search/tests/src/Functional/Hal/SearchPageHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class SearchPageHalJsonCookieTest extends SearchPageResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/search/tests/src/Functional/Rest/SearchPageJsonAnonTest.php b/core/modules/search/tests/src/Functional/Rest/SearchPageJsonAnonTest.php
index 9708192642d5d03e34caa971fb08c5e701d87222..b58490208f0da7128e46ff3ee9601034527f4a33 100644
--- a/core/modules/search/tests/src/Functional/Rest/SearchPageJsonAnonTest.php
+++ b/core/modules/search/tests/src/Functional/Rest/SearchPageJsonAnonTest.php
@@ -21,4 +21,9 @@ class SearchPageJsonAnonTest extends SearchPageResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/search/tests/src/Functional/Rest/SearchPageJsonBasicAuthTest.php b/core/modules/search/tests/src/Functional/Rest/SearchPageJsonBasicAuthTest.php
index f311ce9b4d5033d5bcfb6fea9cdba5a8fe69f80d..615393be6fba3387cd6270c19c4a0544a9bbe96a 100644
--- a/core/modules/search/tests/src/Functional/Rest/SearchPageJsonBasicAuthTest.php
+++ b/core/modules/search/tests/src/Functional/Rest/SearchPageJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class SearchPageJsonBasicAuthTest extends SearchPageResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/search/tests/src/Functional/Rest/SearchPageJsonCookieTest.php b/core/modules/search/tests/src/Functional/Rest/SearchPageJsonCookieTest.php
index 8e7c8899d473f1a39a4f544549e8ef149ffb4e39..ca6c6a3862428099990ba3bfe60ca1b75e6cddb8 100644
--- a/core/modules/search/tests/src/Functional/Rest/SearchPageJsonCookieTest.php
+++ b/core/modules/search/tests/src/Functional/Rest/SearchPageJsonCookieTest.php
@@ -26,4 +26,9 @@ class SearchPageJsonCookieTest extends SearchPageResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/search/tests/src/Functional/Rest/SearchPageXmlAnonTest.php b/core/modules/search/tests/src/Functional/Rest/SearchPageXmlAnonTest.php
index 5f4698ec1bfb7d6e70225d628e6613658d12c30e..3ed7990aa546b14d6a736cc9994d3a974f3d718b 100644
--- a/core/modules/search/tests/src/Functional/Rest/SearchPageXmlAnonTest.php
+++ b/core/modules/search/tests/src/Functional/Rest/SearchPageXmlAnonTest.php
@@ -23,4 +23,9 @@ class SearchPageXmlAnonTest extends SearchPageResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/search/tests/src/Functional/Rest/SearchPageXmlBasicAuthTest.php b/core/modules/search/tests/src/Functional/Rest/SearchPageXmlBasicAuthTest.php
index 7a2c3c8804c9d5f447023e1711bfd6470e5a061d..5381043bee9353ff2ba47b0597e1b3573b686f90 100644
--- a/core/modules/search/tests/src/Functional/Rest/SearchPageXmlBasicAuthTest.php
+++ b/core/modules/search/tests/src/Functional/Rest/SearchPageXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class SearchPageXmlBasicAuthTest extends SearchPageResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/search/tests/src/Functional/Rest/SearchPageXmlCookieTest.php b/core/modules/search/tests/src/Functional/Rest/SearchPageXmlCookieTest.php
index 3ad901d6ef1a568ffd204461765af3693204df98..860981f09f66788bbc74722972d3c88e2c205cb0 100644
--- a/core/modules/search/tests/src/Functional/Rest/SearchPageXmlCookieTest.php
+++ b/core/modules/search/tests/src/Functional/Rest/SearchPageXmlCookieTest.php
@@ -28,4 +28,9 @@ class SearchPageXmlCookieTest extends SearchPageResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/search/tests/src/Functional/SearchAdvancedSearchFormTest.php b/core/modules/search/tests/src/Functional/SearchAdvancedSearchFormTest.php
index 7933dfd9b96572d31062c46c042c940e816530a3..099663ed59d09d81555ca72e5d1f6a56a92587fe 100644
--- a/core/modules/search/tests/src/Functional/SearchAdvancedSearchFormTest.php
+++ b/core/modules/search/tests/src/Functional/SearchAdvancedSearchFormTest.php
@@ -16,6 +16,11 @@ class SearchAdvancedSearchFormTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A node to use for testing.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchBlockTest.php b/core/modules/search/tests/src/Functional/SearchBlockTest.php
index 31e16b13b993cd1fb00b3098b9d556edece4f7e1..07791269c5a74f4d9fbd9cc170d8a92dda6eef24 100644
--- a/core/modules/search/tests/src/Functional/SearchBlockTest.php
+++ b/core/modules/search/tests/src/Functional/SearchBlockTest.php
@@ -17,6 +17,11 @@ class SearchBlockTest extends BrowserTestBase {
    */
   protected static $modules = ['block', 'node', 'search', 'dblog', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The administrative user.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchCommentCountToggleTest.php b/core/modules/search/tests/src/Functional/SearchCommentCountToggleTest.php
index 43f2a311343d9be773b56cff02c7b50ab2fd4d4d..03520359ad50713f2df1569f0db69282081b3867 100644
--- a/core/modules/search/tests/src/Functional/SearchCommentCountToggleTest.php
+++ b/core/modules/search/tests/src/Functional/SearchCommentCountToggleTest.php
@@ -27,6 +27,11 @@ class SearchCommentCountToggleTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'comment', 'search', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to search and post comments.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchCommentTest.php b/core/modules/search/tests/src/Functional/SearchCommentTest.php
index 3c57db0d06c5f3e43df10e687ae114b9dec56a1e..c513be8d53792534a160649be011c5b9d5830780 100644
--- a/core/modules/search/tests/src/Functional/SearchCommentTest.php
+++ b/core/modules/search/tests/src/Functional/SearchCommentTest.php
@@ -26,6 +26,11 @@ class SearchCommentTest extends BrowserTestBase {
    */
   protected static $modules = ['filter', 'node', 'comment', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test subject for comments.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchConfigSettingsFormTest.php b/core/modules/search/tests/src/Functional/SearchConfigSettingsFormTest.php
index f0c9422d6a80ddd978395fe80823b85252a86fcf..fa334854870ebba43bba715e41803d16bcc55d23 100644
--- a/core/modules/search/tests/src/Functional/SearchConfigSettingsFormTest.php
+++ b/core/modules/search/tests/src/Functional/SearchConfigSettingsFormTest.php
@@ -20,6 +20,11 @@ class SearchConfigSettingsFormTest extends BrowserTestBase {
    */
   protected static $modules = ['block', 'dblog', 'node', 'search', 'search_extra_type', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * User who can search and administer search.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchDateIntervalTest.php b/core/modules/search/tests/src/Functional/SearchDateIntervalTest.php
index 84c2d38f00c94dc584f01cb5bffdb8f0bf9d48d5..22c19b9fd898d580518b1423c265635b5354caec 100644
--- a/core/modules/search/tests/src/Functional/SearchDateIntervalTest.php
+++ b/core/modules/search/tests/src/Functional/SearchDateIntervalTest.php
@@ -17,6 +17,11 @@ class SearchDateIntervalTest extends BrowserTestBase {
    */
   protected static $modules = ['language', 'search_date_query_alter', 'node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/search/tests/src/Functional/SearchEmbedFormTest.php b/core/modules/search/tests/src/Functional/SearchEmbedFormTest.php
index c134093df6f2d408b012cf057633becefa0b9a6e..80033b4de78b4449860558169c168342faf1f5be 100644
--- a/core/modules/search/tests/src/Functional/SearchEmbedFormTest.php
+++ b/core/modules/search/tests/src/Functional/SearchEmbedFormTest.php
@@ -16,6 +16,11 @@ class SearchEmbedFormTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search', 'search_embedded_form'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Node used for testing.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchExactTest.php b/core/modules/search/tests/src/Functional/SearchExactTest.php
index 05ad58cff976ddb195ec544f50e41f77bd8dab24..1b77e703c2a84b260da08b8e81e13c6a8b3fa09e 100644
--- a/core/modules/search/tests/src/Functional/SearchExactTest.php
+++ b/core/modules/search/tests/src/Functional/SearchExactTest.php
@@ -16,6 +16,11 @@ class SearchExactTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that the correct number of pager links are found for both keywords and phrases.
    */
diff --git a/core/modules/search/tests/src/Functional/SearchKeywordsConditionsTest.php b/core/modules/search/tests/src/Functional/SearchKeywordsConditionsTest.php
index 4c946894d6d80260c077ca5652e5a5c329c982d1..38faa34e55b5f35368ad1367148aeda0fa8533a7 100644
--- a/core/modules/search/tests/src/Functional/SearchKeywordsConditionsTest.php
+++ b/core/modules/search/tests/src/Functional/SearchKeywordsConditionsTest.php
@@ -21,6 +21,11 @@ class SearchKeywordsConditionsTest extends BrowserTestBase {
    */
   protected static $modules = ['comment', 'search', 'search_extra_type', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to search and post comments.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchLanguageTest.php b/core/modules/search/tests/src/Functional/SearchLanguageTest.php
index d884a4bbc4b11f91a87ffa7f741cd389cadbb08d..539fac67ff3b8e36a31746f53d0ab1956e88df6e 100644
--- a/core/modules/search/tests/src/Functional/SearchLanguageTest.php
+++ b/core/modules/search/tests/src/Functional/SearchLanguageTest.php
@@ -19,6 +19,11 @@ class SearchLanguageTest extends BrowserTestBase {
    */
   protected static $modules = ['language', 'node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Array of nodes available to search.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchMultilingualEntityTest.php b/core/modules/search/tests/src/Functional/SearchMultilingualEntityTest.php
index d823b2e63279281d0868216d0916ca5098601b91..4377ef0b7551e323a0622ef1711673976c341cc7 100644
--- a/core/modules/search/tests/src/Functional/SearchMultilingualEntityTest.php
+++ b/core/modules/search/tests/src/Functional/SearchMultilingualEntityTest.php
@@ -34,6 +34,11 @@ class SearchMultilingualEntityTest extends BrowserTestBase {
    */
   protected static $modules = ['language', 'locale', 'comment', 'node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/search/tests/src/Functional/SearchNodeDiacriticsTest.php b/core/modules/search/tests/src/Functional/SearchNodeDiacriticsTest.php
index e83d84b4ad72e3294d840d1723f57f37dc8eca16..2e7150d8d2d19967748e70ef35f3689703e67fe9 100644
--- a/core/modules/search/tests/src/Functional/SearchNodeDiacriticsTest.php
+++ b/core/modules/search/tests/src/Functional/SearchNodeDiacriticsTest.php
@@ -16,6 +16,11 @@ class SearchNodeDiacriticsTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to use advanced search.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchNodePunctuationTest.php b/core/modules/search/tests/src/Functional/SearchNodePunctuationTest.php
index c0c597ecc5f22f1186487409ad8492cdf72dc52c..02945562a7d7d71712e7dd7868b5d3d4eae73706 100644
--- a/core/modules/search/tests/src/Functional/SearchNodePunctuationTest.php
+++ b/core/modules/search/tests/src/Functional/SearchNodePunctuationTest.php
@@ -16,6 +16,11 @@ class SearchNodePunctuationTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to use advanced search.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchNodeUpdateAndDeletionTest.php b/core/modules/search/tests/src/Functional/SearchNodeUpdateAndDeletionTest.php
index 54095bd636257d352afec1a8a6a5d33970357f1f..6f2a4941ccee8de8ae2ead886dc91f59027e903a 100644
--- a/core/modules/search/tests/src/Functional/SearchNodeUpdateAndDeletionTest.php
+++ b/core/modules/search/tests/src/Functional/SearchNodeUpdateAndDeletionTest.php
@@ -18,6 +18,11 @@ class SearchNodeUpdateAndDeletionTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to access and search content.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchNumberMatchingTest.php b/core/modules/search/tests/src/Functional/SearchNumberMatchingTest.php
index 94eec22daa7acef2fb3fa05a5a135046592f0031..8888b4ddc521286a2bbca6d8857f60e196c779ac 100644
--- a/core/modules/search/tests/src/Functional/SearchNumberMatchingTest.php
+++ b/core/modules/search/tests/src/Functional/SearchNumberMatchingTest.php
@@ -21,6 +21,11 @@ class SearchNumberMatchingTest extends BrowserTestBase {
    */
   protected static $modules = ['dblog', 'node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to administer nodes.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchNumbersTest.php b/core/modules/search/tests/src/Functional/SearchNumbersTest.php
index 60c67394563b3fd7fe87198b5d9edf6e1c0ff8c9..43dd788d177642bc82ccfcdc1d1f226e54dc0577 100644
--- a/core/modules/search/tests/src/Functional/SearchNumbersTest.php
+++ b/core/modules/search/tests/src/Functional/SearchNumbersTest.php
@@ -21,6 +21,11 @@ class SearchNumbersTest extends BrowserTestBase {
    */
   protected static $modules = ['dblog', 'node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to administer nodes.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchPageCacheTagsTest.php b/core/modules/search/tests/src/Functional/SearchPageCacheTagsTest.php
index 320833e51fa66989dd3b35dc1c6a721a372300bb..daa55efaee56c3d82e696e2a4a9c8c17578a0918 100644
--- a/core/modules/search/tests/src/Functional/SearchPageCacheTagsTest.php
+++ b/core/modules/search/tests/src/Functional/SearchPageCacheTagsTest.php
@@ -20,6 +20,11 @@ class SearchPageCacheTagsTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/search/tests/src/Functional/SearchPageOverrideTest.php b/core/modules/search/tests/src/Functional/SearchPageOverrideTest.php
index 5a614e30383b85449e08f0702b946bfcfc599e37..2faac41a5a849d15ed3574d38adcef6ab58e6095 100644
--- a/core/modules/search/tests/src/Functional/SearchPageOverrideTest.php
+++ b/core/modules/search/tests/src/Functional/SearchPageOverrideTest.php
@@ -19,6 +19,11 @@ class SearchPageOverrideTest extends BrowserTestBase {
    */
   protected static $modules = ['search', 'search_extra_type'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to administer search.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchPageTextTest.php b/core/modules/search/tests/src/Functional/SearchPageTextTest.php
index d126bf92711a492eea101fd00e3e7c526fdb06d4..148b4372ce76a49139553662599b3f6d9154f2f8 100644
--- a/core/modules/search/tests/src/Functional/SearchPageTextTest.php
+++ b/core/modules/search/tests/src/Functional/SearchPageTextTest.php
@@ -18,6 +18,11 @@ class SearchPageTextTest extends BrowserTestBase {
    */
   protected static $modules = ['block', 'node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to use advanced search.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchPreprocessLangcodeTest.php b/core/modules/search/tests/src/Functional/SearchPreprocessLangcodeTest.php
index 9f0b991484e05a1e398e7183e15fe489e5df45f6..cdbfb2f6527006db791b42a643e6815cfa9b86eb 100644
--- a/core/modules/search/tests/src/Functional/SearchPreprocessLangcodeTest.php
+++ b/core/modules/search/tests/src/Functional/SearchPreprocessLangcodeTest.php
@@ -16,6 +16,11 @@ class SearchPreprocessLangcodeTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search', 'search_langcode_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test node for searching.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchQueryAlterTest.php b/core/modules/search/tests/src/Functional/SearchQueryAlterTest.php
index e28d63d4aff8aae91a9670c7eae1eb7796ed28e1..bcfd7e2692dee27a0cdafeeb0464626b94d646e9 100644
--- a/core/modules/search/tests/src/Functional/SearchQueryAlterTest.php
+++ b/core/modules/search/tests/src/Functional/SearchQueryAlterTest.php
@@ -16,6 +16,11 @@ class SearchQueryAlterTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search', 'search_query_alter'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that the query alter works.
    */
diff --git a/core/modules/search/tests/src/Functional/SearchRankingTest.php b/core/modules/search/tests/src/Functional/SearchRankingTest.php
index 86c5ff656807fe913c59cd3d0d9aa1960be6a76f..64eb1b776a00ecdaca3c55248a13c181c0a87554 100644
--- a/core/modules/search/tests/src/Functional/SearchRankingTest.php
+++ b/core/modules/search/tests/src/Functional/SearchRankingTest.php
@@ -35,6 +35,11 @@ class SearchRankingTest extends BrowserTestBase {
    */
   protected static $modules = ['node', 'search', 'statistics', 'comment'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/search/tests/src/Functional/SearchSetLocaleTest.php b/core/modules/search/tests/src/Functional/SearchSetLocaleTest.php
index 5dee65879f12172f3594a01d423e880cf42b250b..c0faabccef4aad9361fc37d88cc44ed225dfebe6 100644
--- a/core/modules/search/tests/src/Functional/SearchSetLocaleTest.php
+++ b/core/modules/search/tests/src/Functional/SearchSetLocaleTest.php
@@ -16,6 +16,11 @@ class SearchSetLocaleTest extends BrowserTestBase {
    */
   protected static $modules = ['comment', 'node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A node search plugin instance.
    *
diff --git a/core/modules/search/tests/src/Functional/SearchSimplifyTest.php b/core/modules/search/tests/src/Functional/SearchSimplifyTest.php
index a451063e0a74c33d080142103c3ff9b4afef75b1..127539ef742ae2120b9baba9d84f4c136aed73e3 100644
--- a/core/modules/search/tests/src/Functional/SearchSimplifyTest.php
+++ b/core/modules/search/tests/src/Functional/SearchSimplifyTest.php
@@ -16,6 +16,11 @@ class SearchSimplifyTest extends BrowserTestBase {
    */
   protected static $modules = ['search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that all Unicode characters simplify correctly.
    */
diff --git a/core/modules/search/tests/src/Functional/SearchTokenizerTest.php b/core/modules/search/tests/src/Functional/SearchTokenizerTest.php
index 2e608fc0563309fac4b174d4d88e4aa3383fb153..8b906a72451b8552c6ed192cf231f86eb58ec123 100644
--- a/core/modules/search/tests/src/Functional/SearchTokenizerTest.php
+++ b/core/modules/search/tests/src/Functional/SearchTokenizerTest.php
@@ -16,6 +16,11 @@ class SearchTokenizerTest extends BrowserTestBase {
    */
   protected static $modules = ['search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verifies that strings of CJK characters are tokenized.
    *
diff --git a/core/modules/settings_tray/tests/src/Functional/SettingsTrayTest.php b/core/modules/settings_tray/tests/src/Functional/SettingsTrayTest.php
index aec0392de1dec690ad2ba8b65473a535fdd5c344..2aa98363c63235e73c47cb5cba2d37057473c7d1 100644
--- a/core/modules/settings_tray/tests/src/Functional/SettingsTrayTest.php
+++ b/core/modules/settings_tray/tests/src/Functional/SettingsTrayTest.php
@@ -20,6 +20,11 @@ class SettingsTrayTest extends BrowserTestBase {
     'settings_tray_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Gets the block CSS selector.
    *
diff --git a/core/modules/settings_tray/tests/src/FunctionalJavascript/ConfigAccessTest.php b/core/modules/settings_tray/tests/src/FunctionalJavascript/ConfigAccessTest.php
index 6b15be9425ebda1e6e5373c39ecc2d4307a73b27..c3e604a29f484d5d06370b9d93eee60033a09b5f 100644
--- a/core/modules/settings_tray/tests/src/FunctionalJavascript/ConfigAccessTest.php
+++ b/core/modules/settings_tray/tests/src/FunctionalJavascript/ConfigAccessTest.php
@@ -20,6 +20,11 @@ class ConfigAccessTest extends SettingsTrayTestBase {
     'menu_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/settings_tray/tests/src/FunctionalJavascript/OverriddenConfigurationTest.php b/core/modules/settings_tray/tests/src/FunctionalJavascript/OverriddenConfigurationTest.php
index 97cd4db18f43e56973ad98c596b5ada84fbd1160..ec8afac59cf928686c2864a67d17e63301b5b65d 100644
--- a/core/modules/settings_tray/tests/src/FunctionalJavascript/OverriddenConfigurationTest.php
+++ b/core/modules/settings_tray/tests/src/FunctionalJavascript/OverriddenConfigurationTest.php
@@ -22,6 +22,11 @@ class OverriddenConfigurationTest extends SettingsTrayTestBase {
     'menu_link_content',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/settings_tray/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php b/core/modules/settings_tray/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php
index a543baf1262e7b061244b4e321bce65e12541498..6ee2e51fd9af6f6cff4292b78d622215ca9a1630 100644
--- a/core/modules/settings_tray/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php
+++ b/core/modules/settings_tray/tests/src/FunctionalJavascript/QuickEditIntegrationTest.php
@@ -22,6 +22,11 @@ class QuickEditIntegrationTest extends SettingsTrayTestBase {
     'quickedit',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php b/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
index be89b7c576d42a6e3f99603f42e9695e5e760d8b..bad7a75d672ab4c3783b1b6b24e7813800536751 100644
--- a/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
+++ b/core/modules/settings_tray/tests/src/FunctionalJavascript/SettingsTrayBlockFormTest.php
@@ -23,6 +23,11 @@ class SettingsTrayBlockFormTest extends SettingsTrayTestBase {
     'settings_tray_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonAnonTest.php b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonAnonTest.php
index ba6c8a798d6a59ebbe9a4b0a02e666340f10c6de..6dd633b7e0d695712913c646ee47fa4afabb679e 100644
--- a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonAnonTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class ShortcutHalJsonAnonTest extends ShortcutResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonBasicAuthTest.php b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonBasicAuthTest.php
index 784c3ebc44eb19dc6adcaf03f45db3f38b4b9433..65923fdee342051914637cb37bafdfb05c18b5b1 100644
--- a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonBasicAuthTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ShortcutHalJsonBasicAuthTest extends ShortcutHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonCookieTest.php b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonCookieTest.php
index 7b3b8348d94466268cfc91205b244200c99ea82a..01f152dd493bdceb609c67b4529f37efd02357a0 100644
--- a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonCookieTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutHalJsonCookieTest.php
@@ -15,4 +15,9 @@ class ShortcutHalJsonCookieTest extends ShortcutHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonAnonTest.php b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonAnonTest.php
index b3faae7fbaeb819223d671dbcb5fd0dd0da50c8d..4f1948059523431f2f1abce06f8c81c86a1ff9c4 100644
--- a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonAnonTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ShortcutSetHalJsonAnonTest extends ShortcutSetResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonBasicAuthTest.php b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonBasicAuthTest.php
index d3a70574117ab370266fbe54c81a5319ed51dc8d..5d7b701489252ac08ce27ee487ba5d5eb9c98ad5 100644
--- a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonBasicAuthTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ShortcutSetHalJsonBasicAuthTest extends ShortcutSetHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonCookieTest.php b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonCookieTest.php
index 786936ef08876856300a2281dc795d5cabeefca7..9c8189965e245ada0eb2326ec80321222744f8bd 100644
--- a/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonCookieTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Hal/ShortcutSetHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class ShortcutSetHalJsonCookieTest extends ShortcutSetHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonAnonTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonAnonTest.php
index 04456fac29f12d69622243c72c27bba3c5506273..114dc60d1d0263b61993033edd7d2d62b8afb0a9 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonAnonTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonAnonTest.php
@@ -21,4 +21,9 @@ class ShortcutJsonAnonTest extends ShortcutResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonBasicAuthTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonBasicAuthTest.php
index e0859e3aa3fe60d4abaa193d65a2756a449ce435..c36716e58c243e937c6843d2ce37f7b3adbb9088 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonBasicAuthTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ShortcutJsonBasicAuthTest extends ShortcutResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonCookieTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonCookieTest.php
index 7bf210225be56d4d14f8416ff24111ddabe86e20..fed029af8aa7f8a80f2221ea91743aac93b7fd7b 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonCookieTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutJsonCookieTest.php
@@ -26,4 +26,9 @@ class ShortcutJsonCookieTest extends ShortcutResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonAnonTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonAnonTest.php
index 96750b57b19a793ca8541fc174930434c3f74ffb..ce5f270a21c53beef2afd71d9c949f514084e028 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonAnonTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonAnonTest.php
@@ -21,4 +21,9 @@ class ShortcutSetJsonAnonTest extends ShortcutSetResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonBasicAuthTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonBasicAuthTest.php
index 6ddaf54b0d9f1e365fd215174054001f529138e2..620f1f7220668483326832cc97b933bb15fc4022 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonBasicAuthTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ShortcutSetJsonBasicAuthTest extends ShortcutSetResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonCookieTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonCookieTest.php
index 60fe840606428db0aa53814bde6281599fe6d48b..11676fe190a6a568e0612f9d44e977a878a53687 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonCookieTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetJsonCookieTest.php
@@ -26,4 +26,9 @@ class ShortcutSetJsonCookieTest extends ShortcutSetResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlAnonTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlAnonTest.php
index 75ad14efd47f5e08c4b1c4dffd1f14ab7514f4bf..5dc659538fdf3f616605ac36afbee2df7499b5b0 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlAnonTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlAnonTest.php
@@ -23,4 +23,9 @@ class ShortcutSetXmlAnonTest extends ShortcutSetResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlBasicAuthTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlBasicAuthTest.php
index 50c6e71c23f830a0b1fac9118395b1f104605517..67b32991d55e4ff1d89eab700cefbaf9e1989601 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlBasicAuthTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ShortcutSetXmlBasicAuthTest extends ShortcutSetResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlCookieTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlCookieTest.php
index 71dccd16c36912f4e1ddfbc4b1e15da1e32dd6a4..969fefbaa6dbb2db68a387fdef78003a226c893a 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlCookieTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutSetXmlCookieTest.php
@@ -28,4 +28,9 @@ class ShortcutSetXmlCookieTest extends ShortcutSetResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlAnonTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlAnonTest.php
index 56c5c681a3b8f97373af3e0f8364844542cf48ba..ca58e8bfad971602b42816ac237e6b53880ce423 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlAnonTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlAnonTest.php
@@ -23,4 +23,9 @@ class ShortcutXmlAnonTest extends ShortcutResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlBasicAuthTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlBasicAuthTest.php
index 9645aedaeaea4a279441387043657e4c50b4ed39..209de30ae70e00e5ef3d1eb2ee3601bc953b03b1 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlBasicAuthTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ShortcutXmlBasicAuthTest extends ShortcutResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlCookieTest.php b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlCookieTest.php
index 899b51d88a031e0daa1e200a1654548e40c8d066..d2c4af2021107356966db04cc771cd1f078a5bff 100644
--- a/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlCookieTest.php
+++ b/core/modules/shortcut/tests/src/Functional/Rest/ShortcutXmlCookieTest.php
@@ -28,4 +28,9 @@ class ShortcutXmlCookieTest extends ShortcutResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/shortcut/tests/src/Functional/ShortcutCacheTagsTest.php b/core/modules/shortcut/tests/src/Functional/ShortcutCacheTagsTest.php
index a2282b1ddfc8ca414ad0dcd331708a3769246df4..71720d4442e4b782bfa4ba54ae20a7e09dfb6cfb 100644
--- a/core/modules/shortcut/tests/src/Functional/ShortcutCacheTagsTest.php
+++ b/core/modules/shortcut/tests/src/Functional/ShortcutCacheTagsTest.php
@@ -20,6 +20,11 @@ class ShortcutCacheTagsTest extends EntityCacheTagsTestBase {
    */
   public static $modules = ['shortcut'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/ShortcutLinksTest.php b/core/modules/shortcut/tests/src/Functional/ShortcutLinksTest.php
index aa6a5432b1ef414a403fd79ad7ece58fe395b8ad..8f7bf0aa1bc7ae51354980e71db9e7d19343ced1 100644
--- a/core/modules/shortcut/tests/src/Functional/ShortcutLinksTest.php
+++ b/core/modules/shortcut/tests/src/Functional/ShortcutLinksTest.php
@@ -28,6 +28,11 @@ class ShortcutLinksTest extends ShortcutTestBase {
    */
   public static $modules = ['router_test', 'views', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/ShortcutSetsTest.php b/core/modules/shortcut/tests/src/Functional/ShortcutSetsTest.php
index 5db2f939891e6159c62741f0cb16e2a04634c27f..7b4fcc76acdc6c48dbef1402b76de766044fb7e5 100644
--- a/core/modules/shortcut/tests/src/Functional/ShortcutSetsTest.php
+++ b/core/modules/shortcut/tests/src/Functional/ShortcutSetsTest.php
@@ -18,6 +18,11 @@ class ShortcutSetsTest extends ShortcutTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/shortcut/tests/src/Functional/ShortcutTranslationUITest.php b/core/modules/shortcut/tests/src/Functional/ShortcutTranslationUITest.php
index e3308bd874d70bf0e52a2e0467b516361871a4fd..252d2d0224d4499b41fd77e4d38db8113d6543a1 100644
--- a/core/modules/shortcut/tests/src/Functional/ShortcutTranslationUITest.php
+++ b/core/modules/shortcut/tests/src/Functional/ShortcutTranslationUITest.php
@@ -32,6 +32,11 @@ class ShortcutTranslationUITest extends ContentTranslationUITestBase {
     'toolbar',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/simpletest/tests/src/Functional/SimpletestTest.php b/core/modules/simpletest/tests/src/Functional/SimpletestTest.php
index a7f634deb0fdffbeafd6fd439b9d15b130e29726..781a1bae30ac53a0542be272a840aedf4f2fe5f3 100644
--- a/core/modules/simpletest/tests/src/Functional/SimpletestTest.php
+++ b/core/modules/simpletest/tests/src/Functional/SimpletestTest.php
@@ -18,6 +18,11 @@ class SimpletestTest extends BrowserTestBase {
    */
   public static $modules = ['simpletest'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test that we can uninstall the module without mishap.
    *
diff --git a/core/modules/statistics/tests/src/Functional/StatisticsAdminTest.php b/core/modules/statistics/tests/src/Functional/StatisticsAdminTest.php
index 5efc804b8826686421d90a875622d340ec031abd..cafdf9bbae03538c5810a8101d6fcd50c666e8d4 100644
--- a/core/modules/statistics/tests/src/Functional/StatisticsAdminTest.php
+++ b/core/modules/statistics/tests/src/Functional/StatisticsAdminTest.php
@@ -22,6 +22,11 @@ class StatisticsAdminTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'statistics'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user that has permission to administer statistics.
    *
diff --git a/core/modules/statistics/tests/src/Functional/StatisticsAttachedTest.php b/core/modules/statistics/tests/src/Functional/StatisticsAttachedTest.php
index 42f1a225e5a9c3d82a612c5d83d0f196d5a5323f..9a77f50e06c3a149f15db35951bee858b740c17b 100644
--- a/core/modules/statistics/tests/src/Functional/StatisticsAttachedTest.php
+++ b/core/modules/statistics/tests/src/Functional/StatisticsAttachedTest.php
@@ -19,6 +19,11 @@ class StatisticsAttachedTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'statistics'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/statistics/tests/src/Functional/StatisticsLoggingTest.php b/core/modules/statistics/tests/src/Functional/StatisticsLoggingTest.php
index cfba14e017ad035b9a50aede58ee81005e1601d2..07abf5fdbcbd47eadd3df99720237b382cc0e2db 100644
--- a/core/modules/statistics/tests/src/Functional/StatisticsLoggingTest.php
+++ b/core/modules/statistics/tests/src/Functional/StatisticsLoggingTest.php
@@ -23,6 +23,11 @@ class StatisticsLoggingTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'statistics', 'block', 'locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * User with permissions to create and edit pages.
    *
diff --git a/core/modules/statistics/tests/src/Functional/StatisticsReportsTest.php b/core/modules/statistics/tests/src/Functional/StatisticsReportsTest.php
index f0448110fd478ea42aba89d593e0e03edb6e2c14..0b80251d6cf66aa587d08daae639e5060e305fa5 100644
--- a/core/modules/statistics/tests/src/Functional/StatisticsReportsTest.php
+++ b/core/modules/statistics/tests/src/Functional/StatisticsReportsTest.php
@@ -15,6 +15,11 @@ class StatisticsReportsTest extends StatisticsTestBase {
 
   use AssertPageCacheContextsAndTagsTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the "popular content" block.
    */
diff --git a/core/modules/statistics/tests/src/Functional/StatisticsTokenReplaceTest.php b/core/modules/statistics/tests/src/Functional/StatisticsTokenReplaceTest.php
index 7e99ab3c800de1a31c3d0b70ea7ee651019b3774..6a670988152719d850d1e4ceb804b6bde4f660c3 100644
--- a/core/modules/statistics/tests/src/Functional/StatisticsTokenReplaceTest.php
+++ b/core/modules/statistics/tests/src/Functional/StatisticsTokenReplaceTest.php
@@ -12,6 +12,11 @@
  */
 class StatisticsTokenReplaceTest extends StatisticsTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Creates a node, then tests the statistics tokens generated from it.
    */
diff --git a/core/modules/statistics/tests/src/Functional/Views/IntegrationTest.php b/core/modules/statistics/tests/src/Functional/Views/IntegrationTest.php
index 16018206443bfef3b8b288a8137b29ff99e63834..ebee1ee43d2c9cba0703ed9492d2ee02a1a447c8 100644
--- a/core/modules/statistics/tests/src/Functional/Views/IntegrationTest.php
+++ b/core/modules/statistics/tests/src/Functional/Views/IntegrationTest.php
@@ -21,6 +21,11 @@ class IntegrationTest extends ViewTestBase {
    */
   public static $modules = ['statistics', 'statistics_test_views', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Stores the user object that accesses the page.
    *
diff --git a/core/modules/statistics/tests/src/FunctionalJavascript/StatisticsLoggingTest.php b/core/modules/statistics/tests/src/FunctionalJavascript/StatisticsLoggingTest.php
index acd103e9f69d47b72cd29427fba85b4310603773..c1b7bff2964350875f3d6ecd5f2ab538f0b8e2e1 100644
--- a/core/modules/statistics/tests/src/FunctionalJavascript/StatisticsLoggingTest.php
+++ b/core/modules/statistics/tests/src/FunctionalJavascript/StatisticsLoggingTest.php
@@ -19,6 +19,11 @@ class StatisticsLoggingTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'statistics', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Node for tests.
    *
diff --git a/core/modules/syslog/tests/src/Functional/SyslogTest.php b/core/modules/syslog/tests/src/Functional/SyslogTest.php
index 11b577f2f2429d51e205f84158296161da17d59f..8348cb1ee27a83f5f395f796240a97eba339b21d 100644
--- a/core/modules/syslog/tests/src/Functional/SyslogTest.php
+++ b/core/modules/syslog/tests/src/Functional/SyslogTest.php
@@ -18,6 +18,11 @@ class SyslogTest extends BrowserTestBase {
    */
   public static $modules = ['syslog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the syslog settings page.
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonAnonTest.php
index 77988aa037a6ea036e614e3b4ea633044557fe89..2802bee928501b926124b5b2ee22979b3e766ef1 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonAnonTest.php
@@ -19,6 +19,11 @@ class EntityTestBundleHalJsonAnonTest extends EntityTestBundleResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonBasicAuthTest.php
index 47e44d2d1886006c1be4bee06c46d920c82ad269..0557bfe740981d62143563c95295c222fbf153c4 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class EntityTestBundleHalJsonBasicAuthTest extends EntityTestBundleResourceTestB
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonCookieTest.php
index 3e8b442de7a28ed348af5f2cdbb8a333407b7c90..c604aa900eae1ad6c0fc453ea9e0179b6096309c 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestBundleHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class EntityTestBundleHalJsonCookieTest extends EntityTestBundleResourceTestBase
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonAnonTest.php
index c272a1aa6fd6894beb581b92a1cada79d24552e3..17a65df4ca9904690d86de4c1248d835f7c10fb9 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonAnonTest.php
@@ -22,6 +22,11 @@ class EntityTestHalJsonAnonTest extends EntityTestResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonBasicAuthTest.php
index 18fad4beede41187d09bd03c2fedc520e68340a9..faef8d1cfc1ce06c68815a0a3ec96ee772929519 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityTestHalJsonBasicAuthTest extends EntityTestHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonCookieTest.php
index bee58edc395e341a0ad00fae3e1ec410acb18b7c..10bf4a1ca2ccbe351bd4ef0d96884987da40e988 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class EntityTestHalJsonCookieTest extends EntityTestHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonInternalPropertyNormalizerTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonInternalPropertyNormalizerTest.php
index 73d70d3ff6a2bdbb3c4988d3c191a3c9cc583737..d68315ceb853170ea85c80abfce52d66598da7fc 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonInternalPropertyNormalizerTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestHalJsonInternalPropertyNormalizerTest.php
@@ -22,6 +22,11 @@ class EntityTestHalJsonInternalPropertyNormalizerTest extends EntityTestHalJsonA
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonAnonTest.php
index ca6e395351462757fb55983c9d4a40fdf12a4523..22c6212050498913aa7a8668d895e74270a5d89e 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class EntityTestLabelHalJsonAnonTest extends EntityTestLabelResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonBasicAuthTest.php
index dfae2e40243bfab4d3a3bd8c02024a2036444ba7..4af4063cb5fe72454e8fe90414a514b3ee4e3065 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityTestLabelHalJsonBasicAuthTest extends EntityTestLabelHalJsonAnonTest
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonCookieTest.php
index 3e373404e90f2f827d11f9414ec992febcc18284..f46f586a35e21930f388c272271943864ab95883 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestLabelHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class EntityTestLabelHalJsonCookieTest extends EntityTestLabelHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestMapFieldHalJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestMapFieldHalJsonAnonTest.php
index af1ef4ceaa86a716d8805e80c19e341683dd2f17..dfee26fbd619e43f9aeaf7bbeea7df1752593479 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestMapFieldHalJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Hal/EntityTestMapFieldHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class EntityTestMapFieldHalJsonAnonTest extends EntityTestMapFieldResourceTestBa
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonAnonTest.php
index 08eb70047b7c1ef0af88444a668c362cb61ebbd2..c1abebd0b3429b9d300b89efcdd894982f60b583 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonAnonTest.php
@@ -21,4 +21,9 @@ class EntityTestBundleJsonAnonTest extends EntityTestBundleResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonBasicAuthTest.php
index d1a7adbc9e756c0a618d25f84190226502d50c7b..a6a437ada4587577a5e5adce021bc49d426c84cf 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityTestBundleJsonBasicAuthTest extends EntityTestBundleResourceTestBase
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonCookieTest.php
index 313c9b9908046b1e5d42c433cae254054af03043..b239f41efc82276881bcc8b5ef9c6d0e57986e26 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleJsonCookieTest.php
@@ -26,4 +26,9 @@ class EntityTestBundleJsonCookieTest extends EntityTestBundleResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlAnonTest.php
index e88314b42554ada7b0ae4dabb103ab2fc0d8a14f..8c2d234da2d7b32e7c8dd56597cb995bc4c74da8 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlAnonTest.php
@@ -23,4 +23,9 @@ class EntityTestBundleXmlAnonTest extends EntityTestBundleResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlBasicAuthTest.php
index 701c15ba9f5b0aa670234c34bfa0a1a418c5e8a7..059ca8efbd2c3f737f7f7f3d6f0e62a67a925009 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class EntityTestBundleXmlBasicAuthTest extends EntityTestBundleResourceTestBase
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlCookieTest.php
index 2f3ee3310c8cc404f62d92217076549d6c7458f9..5252b3f351218cce3ff058fea89e6d714015367a 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestBundleXmlCookieTest.php
@@ -28,4 +28,9 @@ class EntityTestBundleXmlCookieTest extends EntityTestBundleResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonAnonTest.php
index 58d15b3aa2c788d07ae676a97a95c740f8a0caca..ff36b51b43fa2225de87471cbb7b403c5c4f9409 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonAnonTest.php
@@ -23,4 +23,9 @@ class EntityTestJsonAnonTest extends EntityTestResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonBasicAuthTest.php
index cd647e8fe3aa09b0b86d73c3e4a10e1aa95b746e..b79bf3cf0393e819677f8769d4a3a285b49cccde 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityTestJsonBasicAuthTest extends EntityTestResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonCookieTest.php
index b76de42b3bf529e3a2340c52cf9e16c3b2a8fc07..9ddb7a700072809c040d296be7ccf17450bb7750 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonCookieTest.php
@@ -26,4 +26,9 @@ class EntityTestJsonCookieTest extends EntityTestResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonInternalPropertyNormalizerTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonInternalPropertyNormalizerTest.php
index 7ac9d89852681024205f8d264c6132eefb099206..ec7868ec47c781500adfa1eeac93109ccc2bae19 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonInternalPropertyNormalizerTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestJsonInternalPropertyNormalizerTest.php
@@ -26,6 +26,11 @@ class EntityTestJsonInternalPropertyNormalizerTest extends EntityTestResourceTes
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonAnonTest.php
index 31a476de39caa4ef4c98550c6210765e29852c31..a122830c99f86f506a4eb808feafc6244cf5b399 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonAnonTest.php
@@ -21,4 +21,9 @@ class EntityTestLabelJsonAnonTest extends EntityTestLabelResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonBasicAuthTest.php
index 61cfea15b229512ce8f830a66891797829c064c8..1332774b4f488adb875c2bed6be4f176073541c9 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityTestLabelJsonBasicAuthTest extends EntityTestLabelResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonCookieTest.php
index 20bb70184f43fe7cb1fa3f46ab92544a91027a5e..5a6153f45c67fe5ce7a6819cf2a35a3a9b13359a 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelJsonCookieTest.php
@@ -26,4 +26,9 @@ class EntityTestLabelJsonCookieTest extends EntityTestLabelResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlAnonTest.php
index ac1bd8685c339d8871c1e0ca2b4130f481c5f714..dc66976988607a4cf1cd78b917b97bc34a1b25c8 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlAnonTest.php
@@ -23,4 +23,9 @@ class EntityTestLabelXmlAnonTest extends EntityTestLabelResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlBasicAuthTest.php
index e671098f2fa328bd8ecccee885ef9fa6a1503e68..067780894f360f0dda1afd1a827ba0fcf6177f93 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class EntityTestLabelXmlBasicAuthTest extends EntityTestLabelResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlCookieTest.php
index f859c7ff8b52297d06e5f223e4ee5a101165971f..5aef8f7466efedd4eab3a57a41a94de31d1faf00 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestLabelXmlCookieTest.php
@@ -28,4 +28,9 @@ class EntityTestLabelXmlCookieTest extends EntityTestLabelResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldJsonAnonTest.php
index 04406803255743471140970d0aad0d8a3d9e9d76..5751c63f54d282230ccb2c1fd324c71af8fdfa85 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldJsonAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldJsonAnonTest.php
@@ -21,4 +21,9 @@ class EntityTestMapFieldJsonAnonTest extends EntityTestMapFieldResourceTestBase
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestTextItemNormalizerTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestTextItemNormalizerTest.php
index 3ae0044aee4cccdfd72d98fcdf2a2d1e1b3974a7..9c3b978cc4223e9e32944b72eff279005d9dca6c 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestTextItemNormalizerTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestTextItemNormalizerTest.php
@@ -19,6 +19,11 @@ class EntityTestTextItemNormalizerTest extends EntityTestResourceTestBase {
    */
   public static $modules = ['filter_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlAnonTest.php
index a5548f9a78b1a604eddc304907dac8a9b8d2dac0..1ddd84f81790431f32c9bcddc698477beacc89e1 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlAnonTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlAnonTest.php
@@ -25,4 +25,9 @@ class EntityTestXmlAnonTest extends EntityTestResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlBasicAuthTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlBasicAuthTest.php
index d0501afb97b30facfc1cf09c335ef3214bb322d1..71f0e81fdac9159d6129c61739b57a5f01b7561e 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlBasicAuthTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class EntityTestXmlBasicAuthTest extends EntityTestResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlCookieTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlCookieTest.php
index 7fe4930fcb26df314733bd58a75520a1fa6c8a68..2fe9035233e060cd8b47f68b1207efb48fb16720 100644
--- a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlCookieTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestXmlCookieTest.php
@@ -28,4 +28,9 @@ class EntityTestXmlCookieTest extends EntityTestResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
index cc7b782d5114a994e651e5a41ad326de2ed69ae6..077c237af56e9a3555e56405850068e2547929b0 100644
--- a/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
+++ b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
@@ -20,6 +20,11 @@
  */
 class FrameworkTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Ajax/OffCanvasDialogTest.php b/core/modules/system/tests/src/Functional/Ajax/OffCanvasDialogTest.php
index c7867221231aa2353f5ad522a859f1a7c67544c6..919e1e7925d0a0909224f544cf82d2bbfe1dfbe9 100644
--- a/core/modules/system/tests/src/Functional/Ajax/OffCanvasDialogTest.php
+++ b/core/modules/system/tests/src/Functional/Ajax/OffCanvasDialogTest.php
@@ -14,6 +14,11 @@
  */
 class OffCanvasDialogTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/core/modules/system/tests/src/Functional/Batch/PageTest.php b/core/modules/system/tests/src/Functional/Batch/PageTest.php
index b979eee4129f7f20313898c92467da2eb8f82377..239b40c515f54c7f091ce22ce74e3267be3e6585 100644
--- a/core/modules/system/tests/src/Functional/Batch/PageTest.php
+++ b/core/modules/system/tests/src/Functional/Batch/PageTest.php
@@ -18,6 +18,11 @@ class PageTest extends BrowserTestBase {
    */
   public static $modules = ['batch_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that the batch API progress page uses the correct theme.
    */
diff --git a/core/modules/system/tests/src/Functional/Batch/ProcessingTest.php b/core/modules/system/tests/src/Functional/Batch/ProcessingTest.php
index 97dc6e7a5f692beae7367c1dba49a75d30fe3b07..bba551189cd8d1e71dd6e8fbafebcbe1bfbf5bc6 100644
--- a/core/modules/system/tests/src/Functional/Batch/ProcessingTest.php
+++ b/core/modules/system/tests/src/Functional/Batch/ProcessingTest.php
@@ -19,6 +19,11 @@ class ProcessingTest extends BrowserTestBase {
    */
   public static $modules = ['batch_test', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests batches triggered outside of form submission.
    */
diff --git a/core/modules/system/tests/src/Functional/Bootstrap/DrupalMessengerServiceTest.php b/core/modules/system/tests/src/Functional/Bootstrap/DrupalMessengerServiceTest.php
index 51404ef18d17a9bc61252814918331853a5a90f3..56db87601fc13cc30f3b5a6c6f2f36b1df71f079 100644
--- a/core/modules/system/tests/src/Functional/Bootstrap/DrupalMessengerServiceTest.php
+++ b/core/modules/system/tests/src/Functional/Bootstrap/DrupalMessengerServiceTest.php
@@ -19,6 +19,11 @@ class DrupalMessengerServiceTest extends BrowserTestBase {
    */
   public static $modules = ['system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests Messenger service.
    */
diff --git a/core/modules/system/tests/src/Functional/Cache/ClearTest.php b/core/modules/system/tests/src/Functional/Cache/ClearTest.php
index 905f010759e8d1ded457c9340e2d08ce39b1c356..fe4add638868bfa71d23629c935ea6403daff7e6 100644
--- a/core/modules/system/tests/src/Functional/Cache/ClearTest.php
+++ b/core/modules/system/tests/src/Functional/Cache/ClearTest.php
@@ -12,6 +12,11 @@
 
 class ClearTest extends CacheTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     $this->defaultBin = 'render';
     $this->defaultValue = $this->randomMachineName(10);
diff --git a/core/modules/system/tests/src/Functional/Cache/SessionExistsCacheContextTest.php b/core/modules/system/tests/src/Functional/Cache/SessionExistsCacheContextTest.php
index 78fb983a612cc2156baecf34beac89529aefefc3..23ad7abaa18c02fa4a677c7ed608a003ca041d50 100644
--- a/core/modules/system/tests/src/Functional/Cache/SessionExistsCacheContextTest.php
+++ b/core/modules/system/tests/src/Functional/Cache/SessionExistsCacheContextTest.php
@@ -19,6 +19,11 @@ class SessionExistsCacheContextTest extends BrowserTestBase {
    */
   public static $modules = ['session_exists_cache_context_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests \Drupal\Core\Cache\Context\SessionExistsCacheContext::getContext().
    */
diff --git a/core/modules/system/tests/src/Functional/Common/AlterTest.php b/core/modules/system/tests/src/Functional/Common/AlterTest.php
index 00b6e5be452defa2e66a47416f0b67d53ce9e88e..e96dd4c2da330634b34bb32e63496b6dd133095e 100644
--- a/core/modules/system/tests/src/Functional/Common/AlterTest.php
+++ b/core/modules/system/tests/src/Functional/Common/AlterTest.php
@@ -18,6 +18,11 @@ class AlterTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'common_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if the theme has been altered.
    */
diff --git a/core/modules/system/tests/src/Functional/Common/EarlyRenderingControllerTest.php b/core/modules/system/tests/src/Functional/Common/EarlyRenderingControllerTest.php
index 9d6c0af5d10be511791aec72a7e217098f10c40b..9595abbfaf7b44135eb6f0763f15e2fd9f4f9cf0 100644
--- a/core/modules/system/tests/src/Functional/Common/EarlyRenderingControllerTest.php
+++ b/core/modules/system/tests/src/Functional/Common/EarlyRenderingControllerTest.php
@@ -22,6 +22,11 @@ class EarlyRenderingControllerTest extends BrowserTestBase {
    */
   public static $modules = ['system', 'early_rendering_controller_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests theme preprocess functions being able to attach assets.
    */
diff --git a/core/modules/system/tests/src/Functional/Common/FormatDateTest.php b/core/modules/system/tests/src/Functional/Common/FormatDateTest.php
index a595db77809d6005255443497729964c548ee45c..b2ff7b1a00e1c4ea1305e20f09256ff5c36e8a1a 100644
--- a/core/modules/system/tests/src/Functional/Common/FormatDateTest.php
+++ b/core/modules/system/tests/src/Functional/Common/FormatDateTest.php
@@ -11,6 +11,11 @@
  */
 class FormatDateTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests admin-defined formats in DateFormatterInterface::format().
    */
diff --git a/core/modules/system/tests/src/Functional/Common/RenderWebTest.php b/core/modules/system/tests/src/Functional/Common/RenderWebTest.php
index 65d260403912e63a375cc3c88ec4929fc1b0a157..5e64bfa92c292e980ecc1b73813de5624862f995 100644
--- a/core/modules/system/tests/src/Functional/Common/RenderWebTest.php
+++ b/core/modules/system/tests/src/Functional/Common/RenderWebTest.php
@@ -23,6 +23,11 @@ class RenderWebTest extends BrowserTestBase {
    */
   public static $modules = ['common_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Asserts the cache context for the wrapper format is always present.
    */
diff --git a/core/modules/system/tests/src/Functional/Common/UrlTest.php b/core/modules/system/tests/src/Functional/Common/UrlTest.php
index bdddea572c73522081c8ccf1153e8609c3208585..d304e122e0ace446021db28f91d89a78b949d949 100644
--- a/core/modules/system/tests/src/Functional/Common/UrlTest.php
+++ b/core/modules/system/tests/src/Functional/Common/UrlTest.php
@@ -24,6 +24,11 @@ class UrlTest extends BrowserTestBase {
 
   public static $modules = ['common_test', 'url_alter_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Confirms that invalid URLs are filtered in link generating functions.
    */
diff --git a/core/modules/system/tests/src/Functional/Condition/ConditionFormTest.php b/core/modules/system/tests/src/Functional/Condition/ConditionFormTest.php
index adefc4392e620dbba4ae3b6f0eed63ded38a5c3f..2cdaabeb3ee0af96ed74c7d16b415c2b02b6c279 100644
--- a/core/modules/system/tests/src/Functional/Condition/ConditionFormTest.php
+++ b/core/modules/system/tests/src/Functional/Condition/ConditionFormTest.php
@@ -18,6 +18,11 @@ class ConditionFormTest extends BrowserTestBase {
 
   public static $modules = ['node', 'condition_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Submit the condition_node_type_test_form to test condition forms.
    */
diff --git a/core/modules/system/tests/src/Functional/CsrfRequestHeaderTest.php b/core/modules/system/tests/src/Functional/CsrfRequestHeaderTest.php
index 0bb9016c4819a00e4766da008aa4d156b3041614..9707141734bbcf891ca91f7bfc50e9279317e49b 100644
--- a/core/modules/system/tests/src/Functional/CsrfRequestHeaderTest.php
+++ b/core/modules/system/tests/src/Functional/CsrfRequestHeaderTest.php
@@ -19,6 +19,11 @@ class CsrfRequestHeaderTest extends BrowserTestBase {
    */
   public static $modules = ['system', 'csrf_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests access to routes protected by CSRF request header requirements.
    *
diff --git a/core/modules/system/tests/src/Functional/Database/SelectPagerDefaultTest.php b/core/modules/system/tests/src/Functional/Database/SelectPagerDefaultTest.php
index e4e83d2d9fedf15ef604e341cc76c0f2c32fab06..a38a5f0180f31769c8e0d80f6fe529298cba0d02 100644
--- a/core/modules/system/tests/src/Functional/Database/SelectPagerDefaultTest.php
+++ b/core/modules/system/tests/src/Functional/Database/SelectPagerDefaultTest.php
@@ -13,6 +13,11 @@
  */
 class SelectPagerDefaultTest extends DatabaseTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Confirms that a pager query returns the correct results.
    *
diff --git a/core/modules/system/tests/src/Functional/Database/SelectTableSortDefaultTest.php b/core/modules/system/tests/src/Functional/Database/SelectTableSortDefaultTest.php
index ee69dec94589ba85256faf36011b3bab9976e678..7e2e2e9a676f8217e374e75fb57d0f1eea7ea58b 100644
--- a/core/modules/system/tests/src/Functional/Database/SelectTableSortDefaultTest.php
+++ b/core/modules/system/tests/src/Functional/Database/SelectTableSortDefaultTest.php
@@ -11,6 +11,11 @@
  */
 class SelectTableSortDefaultTest extends DatabaseTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Confirms that a tablesort query returns the correct results.
    *
diff --git a/core/modules/system/tests/src/Functional/Database/TemporaryQueryTest.php b/core/modules/system/tests/src/Functional/Database/TemporaryQueryTest.php
index f44073571a8ced01a1e523adc3a80b6f750d276c..c31b96bb5b98ce31ef41fef69178d553ddf57eae 100644
--- a/core/modules/system/tests/src/Functional/Database/TemporaryQueryTest.php
+++ b/core/modules/system/tests/src/Functional/Database/TemporaryQueryTest.php
@@ -16,6 +16,11 @@ class TemporaryQueryTest extends DatabaseTestBase {
    */
   public static $modules = ['database_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Returns the number of rows of a table.
    */
diff --git a/core/modules/system/tests/src/Functional/Datetime/DrupalDateTimeTest.php b/core/modules/system/tests/src/Functional/Datetime/DrupalDateTimeTest.php
index 6843e54f753711cd7bb9e7c3237f379dd55e642e..cb57699c5f1ed7af3d3dc990cfb22aeded819bbb 100644
--- a/core/modules/system/tests/src/Functional/Datetime/DrupalDateTimeTest.php
+++ b/core/modules/system/tests/src/Functional/Datetime/DrupalDateTimeTest.php
@@ -18,6 +18,11 @@ class DrupalDateTimeTest extends BrowserTestBase {
    */
   public static $modules = [];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test setup.
    */
diff --git a/core/modules/system/tests/src/Functional/DrupalKernel/ContainerRebuildWebTest.php b/core/modules/system/tests/src/Functional/DrupalKernel/ContainerRebuildWebTest.php
index 828b92f2891341442847d94ceb57a6a4d406faa9..93deab12b8e0b39e8961a3cf059183ebebada710 100644
--- a/core/modules/system/tests/src/Functional/DrupalKernel/ContainerRebuildWebTest.php
+++ b/core/modules/system/tests/src/Functional/DrupalKernel/ContainerRebuildWebTest.php
@@ -16,6 +16,11 @@ class ContainerRebuildWebTest extends BrowserTestBase {
    */
   public static $modules = ['service_provider_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Sets a different deployment identifier.
    */
diff --git a/core/modules/system/tests/src/Functional/DrupalKernel/ContentNegotiationTest.php b/core/modules/system/tests/src/Functional/DrupalKernel/ContentNegotiationTest.php
index 58157369b3db186b02a5f096c0a36b1d1fdfb2df..a57b941e2342a14cf649fd463d6b2ea35cc2c006 100644
--- a/core/modules/system/tests/src/Functional/DrupalKernel/ContentNegotiationTest.php
+++ b/core/modules/system/tests/src/Functional/DrupalKernel/ContentNegotiationTest.php
@@ -11,6 +11,11 @@
  */
 class ContentNegotiationTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verifies HTML responses for bogus Accept headers.
    *
diff --git a/core/modules/system/tests/src/Functional/Entity/EntityAddUITest.php b/core/modules/system/tests/src/Functional/Entity/EntityAddUITest.php
index a16614f1460fc19400e14d161259a2edce309b2d..3e8d187dbe0dec5ce38d3d1b3cbd867c8eac3c4b 100644
--- a/core/modules/system/tests/src/Functional/Entity/EntityAddUITest.php
+++ b/core/modules/system/tests/src/Functional/Entity/EntityAddUITest.php
@@ -19,6 +19,11 @@ class EntityAddUITest extends BrowserTestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the add page for an entity type using bundle entities.
    */
diff --git a/core/modules/system/tests/src/Functional/Entity/EntityFormTest.php b/core/modules/system/tests/src/Functional/Entity/EntityFormTest.php
index 7b497bf417f20d1b1859fffd47ba0ec244fd729f..f6bd340dbb19ca36262d32d32b4ee74378f9588a 100644
--- a/core/modules/system/tests/src/Functional/Entity/EntityFormTest.php
+++ b/core/modules/system/tests/src/Functional/Entity/EntityFormTest.php
@@ -20,6 +20,11 @@ class EntityFormTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $web_user = $this->drupalCreateUser(['administer entity_test content', 'view test entity']);
diff --git a/core/modules/system/tests/src/Functional/Entity/EntityListBuilderTest.php b/core/modules/system/tests/src/Functional/Entity/EntityListBuilderTest.php
index dec8dd8c71336d335760db171827eec821aecf37..5a03e80ef8091ff41be82a8587a0f42df7affe23 100644
--- a/core/modules/system/tests/src/Functional/Entity/EntityListBuilderTest.php
+++ b/core/modules/system/tests/src/Functional/Entity/EntityListBuilderTest.php
@@ -18,6 +18,11 @@ class EntityListBuilderTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Entity/EntityOperationsTest.php b/core/modules/system/tests/src/Functional/Entity/EntityOperationsTest.php
index f881a94bb5b7e106d193fd5d07f772321d95bf52..07d58b6517dac3d50491eaabf11b53519c6ab425 100644
--- a/core/modules/system/tests/src/Functional/Entity/EntityOperationsTest.php
+++ b/core/modules/system/tests/src/Functional/Entity/EntityOperationsTest.php
@@ -19,6 +19,11 @@ class EntityOperationsTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/system/tests/src/Functional/Entity/EntityRevisionsTest.php b/core/modules/system/tests/src/Functional/Entity/EntityRevisionsTest.php
index efc5a82386be11cbb235c854908bff5412ac1cb1..18bfc1824978b7ceeeae4f2875c7d242248ccaa6 100644
--- a/core/modules/system/tests/src/Functional/Entity/EntityRevisionsTest.php
+++ b/core/modules/system/tests/src/Functional/Entity/EntityRevisionsTest.php
@@ -24,6 +24,11 @@ class EntityRevisionsTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to administer entity_test content.
    *
diff --git a/core/modules/system/tests/src/Functional/Entity/EntityTranslationFormTest.php b/core/modules/system/tests/src/Functional/Entity/EntityTranslationFormTest.php
index e008e71e1f985c9b13d514eaa134ba13eb715814..a4472405e524c7c942b6de73451bbb2d4935856b 100644
--- a/core/modules/system/tests/src/Functional/Entity/EntityTranslationFormTest.php
+++ b/core/modules/system/tests/src/Functional/Entity/EntityTranslationFormTest.php
@@ -21,6 +21,11 @@ class EntityTranslationFormTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'language', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $langcodes;
 
   protected function setUp() {
diff --git a/core/modules/system/tests/src/Functional/Entity/EntityViewControllerTest.php b/core/modules/system/tests/src/Functional/Entity/EntityViewControllerTest.php
index 3bd84036864a1f1495f91739482255521e09a1d3..bdc63f2dbc79ea6719750771a588ee3b7c107eb0 100644
--- a/core/modules/system/tests/src/Functional/Entity/EntityViewControllerTest.php
+++ b/core/modules/system/tests/src/Functional/Entity/EntityViewControllerTest.php
@@ -19,6 +19,11 @@ class EntityViewControllerTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Array of test entities.
    *
diff --git a/core/modules/system/tests/src/Functional/Entity/Update/UpdateApiEntityDefinitionUpdateTest.php b/core/modules/system/tests/src/Functional/Entity/Update/UpdateApiEntityDefinitionUpdateTest.php
index 07352cbc07e9ec5829ccbb1b56d3988e5dca4c8d..7efc11b74bfbebd57a62029358e076e080581ab2 100644
--- a/core/modules/system/tests/src/Functional/Entity/Update/UpdateApiEntityDefinitionUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Entity/Update/UpdateApiEntityDefinitionUpdateTest.php
@@ -22,6 +22,11 @@ class UpdateApiEntityDefinitionUpdateTest extends BrowserTestBase {
    */
   protected static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/File/ConfigTest.php b/core/modules/system/tests/src/Functional/File/ConfigTest.php
index 9d0761fd16d4f288604a5746b472c185aee95c0c..f44e8a924a869c5951847a68bec082fddf03c18a 100644
--- a/core/modules/system/tests/src/Functional/File/ConfigTest.php
+++ b/core/modules/system/tests/src/Functional/File/ConfigTest.php
@@ -11,6 +11,11 @@
  */
 class ConfigTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->drupalLogin($this->drupalCreateUser(['administer site configuration']));
diff --git a/core/modules/system/tests/src/Functional/File/FileSaveHtaccessLoggingTest.php b/core/modules/system/tests/src/Functional/File/FileSaveHtaccessLoggingTest.php
index 7004bc9bcf28e3192d9cb36453dd511dd2210bb6..62a0b7a23d5b1cbf0ad61ce04867b1ba3e9cb426 100644
--- a/core/modules/system/tests/src/Functional/File/FileSaveHtaccessLoggingTest.php
+++ b/core/modules/system/tests/src/Functional/File/FileSaveHtaccessLoggingTest.php
@@ -14,6 +14,11 @@ class FileSaveHtaccessLoggingTest extends BrowserTestBase {
 
   protected static $modules = ['dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests file_save_htaccess().
    */
diff --git a/core/modules/system/tests/src/Functional/FileTransfer/FileTransferTest.php b/core/modules/system/tests/src/Functional/FileTransfer/FileTransferTest.php
index a15a92a6dbb21296578102a58f9932984cde4414..3ec2cbccd87b69472f5d14a45bb5fa11a7ad479f 100644
--- a/core/modules/system/tests/src/Functional/FileTransfer/FileTransferTest.php
+++ b/core/modules/system/tests/src/Functional/FileTransfer/FileTransferTest.php
@@ -18,6 +18,11 @@ class FileTransferTest extends BrowserTestBase {
   protected $password = 'password';
   protected $port = '42';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->testConnection = TestFileTransfer::factory($this->root, ['hostname' => $this->hostname, 'username' => $this->username, 'password' => $this->password, 'port' => $this->port]);
diff --git a/core/modules/system/tests/src/Functional/Form/AlterTest.php b/core/modules/system/tests/src/Functional/Form/AlterTest.php
index 622a3d1ead105cb72c63435839314db6641acad2..d1f9667acbdbcf81a70f84bb0b19f7b2ff79f38f 100644
--- a/core/modules/system/tests/src/Functional/Form/AlterTest.php
+++ b/core/modules/system/tests/src/Functional/Form/AlterTest.php
@@ -19,6 +19,11 @@ class AlterTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests execution order of hook_form_alter() and hook_form_FORM_ID_alter().
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ArbitraryRebuildTest.php b/core/modules/system/tests/src/Functional/Form/ArbitraryRebuildTest.php
index 8aa36f08bd243f67a2a2db2f85fc18db4ac2a231..ce1ebbd7c36d82955edb445b3da51776e96ec0fc 100644
--- a/core/modules/system/tests/src/Functional/Form/ArbitraryRebuildTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ArbitraryRebuildTest.php
@@ -20,6 +20,11 @@ class ArbitraryRebuildTest extends BrowserTestBase {
    */
   public static $modules = ['text', 'form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/system/tests/src/Functional/Form/CheckboxTest.php b/core/modules/system/tests/src/Functional/Form/CheckboxTest.php
index a4d9c0904a7194655c3272094bdf79759d518b39..66f7eab1d1acfc3d5170839e4e8516f296d05968 100644
--- a/core/modules/system/tests/src/Functional/Form/CheckboxTest.php
+++ b/core/modules/system/tests/src/Functional/Form/CheckboxTest.php
@@ -20,6 +20,11 @@ class CheckboxTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testFormCheckbox() {
     // Ensure that the checked state is determined and rendered correctly for
     // tricky combinations of default and return values.
diff --git a/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php b/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php
index ad5a74b691393b7839b0501d64e801e61f5a9380..421ef4196e07e207c6399b79f6998ab502de413e 100644
--- a/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php
@@ -20,6 +20,11 @@ class ConfirmFormTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testConfirmForm() {
     // Test the building of the form.
     $this->drupalGet('form-test/confirm-form');
diff --git a/core/modules/system/tests/src/Functional/Form/ElementTest.php b/core/modules/system/tests/src/Functional/Form/ElementTest.php
index eb167d428f7bc310892b6b4766a74112a5c21740..1ebd39e5351749c7b03cc0bd038a02c268b798a2 100644
--- a/core/modules/system/tests/src/Functional/Form/ElementTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ElementTest.php
@@ -19,6 +19,11 @@ class ElementTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests placeholder text for elements that support placeholders.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ElementsAccessTest.php b/core/modules/system/tests/src/Functional/Form/ElementsAccessTest.php
index 1a92893c3929b4ab575b40696e75ce1de91fe857..2167cbb58f6badc972f526cff3fd01207174a91b 100644
--- a/core/modules/system/tests/src/Functional/Form/ElementsAccessTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ElementsAccessTest.php
@@ -18,6 +18,11 @@ class ElementsAccessTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensures that child values are still processed when #access = FALSE.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ElementsContainerTest.php b/core/modules/system/tests/src/Functional/Form/ElementsContainerTest.php
index a7d404b86be5d7c7d12f5bf4bf6a3c6f92660590..874cee6dcaa77e103499cda032b9b1461c236fd1 100644
--- a/core/modules/system/tests/src/Functional/Form/ElementsContainerTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ElementsContainerTest.php
@@ -18,6 +18,11 @@ class ElementsContainerTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the #optional container property.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ElementsLabelsTest.php b/core/modules/system/tests/src/Functional/Form/ElementsLabelsTest.php
index 91f3ec4a59d47d3d1e35b380ae4a5655c38fd62e..0065110ee6cd94392b9139deffb731e677c2a126 100644
--- a/core/modules/system/tests/src/Functional/Form/ElementsLabelsTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ElementsLabelsTest.php
@@ -19,6 +19,11 @@ class ElementsLabelsTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test form elements, labels, title attributes and required marks output
    * correctly and have the correct label option class if needed.
diff --git a/core/modules/system/tests/src/Functional/Form/ElementsTableSelectTest.php b/core/modules/system/tests/src/Functional/Form/ElementsTableSelectTest.php
index f377c0abf60ace5a0af955fc8e3e871415a92516..90ded5760d22124789f91aefa86d8e7f57ba3484 100644
--- a/core/modules/system/tests/src/Functional/Form/ElementsTableSelectTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ElementsTableSelectTest.php
@@ -19,6 +19,11 @@ class ElementsTableSelectTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test the display of checkboxes when #multiple is TRUE.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ElementsVerticalTabsTest.php b/core/modules/system/tests/src/Functional/Form/ElementsVerticalTabsTest.php
index 34ca1c9cf81103c0af3188ab834806a4db10eba3..e90c4dfe3d9904a4b47fe8b4cdb05b8f321f4482 100644
--- a/core/modules/system/tests/src/Functional/Form/ElementsVerticalTabsTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ElementsVerticalTabsTest.php
@@ -20,6 +20,11 @@ class ElementsVerticalTabsTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to access vertical_tab_test_tabs.
    *
diff --git a/core/modules/system/tests/src/Functional/Form/EmailTest.php b/core/modules/system/tests/src/Functional/Form/EmailTest.php
index 2fe6ebe9078f2598d9813e418383d4648a927b9b..678f081ebe16a1ae6adbdcf9f51f844e122092d4 100644
--- a/core/modules/system/tests/src/Functional/Form/EmailTest.php
+++ b/core/modules/system/tests/src/Functional/Form/EmailTest.php
@@ -19,6 +19,11 @@ class EmailTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that #type 'email' fields are properly validated.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/FormObjectTest.php b/core/modules/system/tests/src/Functional/Form/FormObjectTest.php
index e2c00f5d17a8734aba9f1d543ff91ae48fb6f468..c2f89735c90036087a68f36977bfddd33596eea7 100644
--- a/core/modules/system/tests/src/Functional/Form/FormObjectTest.php
+++ b/core/modules/system/tests/src/Functional/Form/FormObjectTest.php
@@ -18,6 +18,11 @@ class FormObjectTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests using an object as the form callback.
    *
diff --git a/core/modules/system/tests/src/Functional/Form/FormStoragePageCacheTest.php b/core/modules/system/tests/src/Functional/Form/FormStoragePageCacheTest.php
index 474a35b55a97a5c4065867ffcc333a2ff86e750e..9f63ead122494045bc77177d6791735bcf00cee7 100644
--- a/core/modules/system/tests/src/Functional/Form/FormStoragePageCacheTest.php
+++ b/core/modules/system/tests/src/Functional/Form/FormStoragePageCacheTest.php
@@ -16,6 +16,11 @@ class FormStoragePageCacheTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Form/FormTest.php b/core/modules/system/tests/src/Functional/Form/FormTest.php
index 0551c88322d3b9edae967acb4352dac36069710d..5458f1ef3a9698635d0d3856ed1858048f6333b6 100644
--- a/core/modules/system/tests/src/Functional/Form/FormTest.php
+++ b/core/modules/system/tests/src/Functional/Form/FormTest.php
@@ -28,6 +28,11 @@ class FormTest extends BrowserTestBase {
    */
   public static $modules = ['filter', 'form_test', 'file', 'datetime'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/system/tests/src/Functional/Form/LanguageSelectElementTest.php b/core/modules/system/tests/src/Functional/Form/LanguageSelectElementTest.php
index 1e77250b60e72421a58708a35a670e2dbd026223..f9f10ca8b8b9ffc121a2b06e0d99903c2c110630 100644
--- a/core/modules/system/tests/src/Functional/Form/LanguageSelectElementTest.php
+++ b/core/modules/system/tests/src/Functional/Form/LanguageSelectElementTest.php
@@ -23,6 +23,11 @@ class LanguageSelectElementTest extends BrowserTestBase {
    */
   public static $modules = ['form_test', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that the options printed by the language select element are correct.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php b/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php
index 1e1b2fc579ff1b069434585bea0d191cceea860e..0faac2821a9b5493121612ea28c0331d7a48cd36 100644
--- a/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ModulesListFormWebTest.php
@@ -16,6 +16,11 @@ class ModulesListFormWebTest extends BrowserTestBase {
    */
   public static $modules = ['system_test', 'help'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Form/RebuildTest.php b/core/modules/system/tests/src/Functional/Form/RebuildTest.php
index 3e951e2e802c9d5012879c4109b2c8f749a8b617..6b87f6304225235fa625a90c3238ad7d8c324f67 100644
--- a/core/modules/system/tests/src/Functional/Form/RebuildTest.php
+++ b/core/modules/system/tests/src/Functional/Form/RebuildTest.php
@@ -18,6 +18,11 @@ class RebuildTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user for testing.
    *
diff --git a/core/modules/system/tests/src/Functional/Form/RedirectTest.php b/core/modules/system/tests/src/Functional/Form/RedirectTest.php
index baaed0d1ded05e3a7702174d65326f7aef20724d..e66cc3830873aff79cb4f7b35cc813b3842d11b7 100644
--- a/core/modules/system/tests/src/Functional/Form/RedirectTest.php
+++ b/core/modules/system/tests/src/Functional/Form/RedirectTest.php
@@ -19,6 +19,11 @@ class RedirectTest extends BrowserTestBase {
    */
   public static $modules = ['form_test', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests form redirection.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ResponseTest.php b/core/modules/system/tests/src/Functional/Form/ResponseTest.php
index de5d8fd6c7a62483192c992e44f9bb5a6de8465a..4707a47e501e8f79863e339fa7f083af544fe41b 100644
--- a/core/modules/system/tests/src/Functional/Form/ResponseTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ResponseTest.php
@@ -19,6 +19,11 @@ class ResponseTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that enforced responses propagate through subscribers and middleware.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/StateValuesCleanAdvancedTest.php b/core/modules/system/tests/src/Functional/Form/StateValuesCleanAdvancedTest.php
index 7341e18994de7cc1ed7546afe227347dc3f983f4..56dab576c1ce4337b9db7fc7fbc0a19b682fa0a7 100644
--- a/core/modules/system/tests/src/Functional/Form/StateValuesCleanAdvancedTest.php
+++ b/core/modules/system/tests/src/Functional/Form/StateValuesCleanAdvancedTest.php
@@ -25,6 +25,11 @@ class StateValuesCleanAdvancedTest extends BrowserTestBase {
    */
   public static $modules = ['file', 'form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An image file path for uploading.
    *
diff --git a/core/modules/system/tests/src/Functional/Form/StateValuesCleanTest.php b/core/modules/system/tests/src/Functional/Form/StateValuesCleanTest.php
index a77b11fd7535df7e1cadcb1898c75d3b8ca58cea..b5bd856de1c96329fe773014e92e661ff231882c 100644
--- a/core/modules/system/tests/src/Functional/Form/StateValuesCleanTest.php
+++ b/core/modules/system/tests/src/Functional/Form/StateValuesCleanTest.php
@@ -21,6 +21,11 @@ class StateValuesCleanTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests \Drupal\Core\Form\FormState::cleanValues().
    */
diff --git a/core/modules/system/tests/src/Functional/Form/StorageTest.php b/core/modules/system/tests/src/Functional/Form/StorageTest.php
index 95969fde5a2c82af4a2e399b634fe882dbf1142e..32c915e047a64c79159b49fd27930e5fc7734444 100644
--- a/core/modules/system/tests/src/Functional/Form/StorageTest.php
+++ b/core/modules/system/tests/src/Functional/Form/StorageTest.php
@@ -27,6 +27,11 @@ class StorageTest extends BrowserTestBase {
    */
   public static $modules = ['form_test', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Form/SystemConfigFormTest.php b/core/modules/system/tests/src/Functional/Form/SystemConfigFormTest.php
index 09ad06ac8c265f2983095d5936d0467b264daad9..e5c5e17ddb1c9d358dab9ca0dad4d8e0f665c9df 100644
--- a/core/modules/system/tests/src/Functional/Form/SystemConfigFormTest.php
+++ b/core/modules/system/tests/src/Functional/Form/SystemConfigFormTest.php
@@ -18,6 +18,11 @@ class SystemConfigFormTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the SystemConfigFormTestBase class.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/UrlTest.php b/core/modules/system/tests/src/Functional/Form/UrlTest.php
index 82d227bbdf95fbdd7de618f2362ad0b7e482d841..02197602f78153767a8927fa9d0ec00c7684b20d 100644
--- a/core/modules/system/tests/src/Functional/Form/UrlTest.php
+++ b/core/modules/system/tests/src/Functional/Form/UrlTest.php
@@ -21,6 +21,11 @@ class UrlTest extends BrowserTestBase {
 
   protected $profile = 'testing';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that #type 'url' fields are properly validated and trimmed.
    */
diff --git a/core/modules/system/tests/src/Functional/Form/ValidationTest.php b/core/modules/system/tests/src/Functional/Form/ValidationTest.php
index ccb15ade16dd06ad523adf93bc2889805803f27c..cadf427581ebbf94959fdf0ca26c837dea879830 100644
--- a/core/modules/system/tests/src/Functional/Form/ValidationTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ValidationTest.php
@@ -20,6 +20,11 @@ class ValidationTest extends BrowserTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests #element_validate and #validate.
    */
diff --git a/core/modules/system/tests/src/Functional/Hal/ActionHalJsonAnonTest.php b/core/modules/system/tests/src/Functional/Hal/ActionHalJsonAnonTest.php
index eb19bac6f12923171602943967ae09102621d5f7..6c0ad70cbcd891ed49eae39e3019bf12933d077c 100644
--- a/core/modules/system/tests/src/Functional/Hal/ActionHalJsonAnonTest.php
+++ b/core/modules/system/tests/src/Functional/Hal/ActionHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ActionHalJsonAnonTest extends ActionResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Hal/ActionHalJsonBasicAuthTest.php b/core/modules/system/tests/src/Functional/Hal/ActionHalJsonBasicAuthTest.php
index 7441f6ab4bcd4a8db619408433ca69b203d7258b..13daf5b04121d259558c824d95d35681614e7a07 100644
--- a/core/modules/system/tests/src/Functional/Hal/ActionHalJsonBasicAuthTest.php
+++ b/core/modules/system/tests/src/Functional/Hal/ActionHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class ActionHalJsonBasicAuthTest extends ActionResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Hal/ActionHalJsonCookieTest.php b/core/modules/system/tests/src/Functional/Hal/ActionHalJsonCookieTest.php
index f013032e85169fb21d2391ca551ba65bec9feb8a..2a9c6178b950159712a9f2f9730930ab76f9696c 100644
--- a/core/modules/system/tests/src/Functional/Hal/ActionHalJsonCookieTest.php
+++ b/core/modules/system/tests/src/Functional/Hal/ActionHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ActionHalJsonCookieTest extends ActionResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Hal/MenuHalJsonAnonTest.php b/core/modules/system/tests/src/Functional/Hal/MenuHalJsonAnonTest.php
index 0200624b162c34c0dfad73b73d7a3a42d38d03b0..04dd30e6ce2d6df3464531c884989d693d9f9b84 100644
--- a/core/modules/system/tests/src/Functional/Hal/MenuHalJsonAnonTest.php
+++ b/core/modules/system/tests/src/Functional/Hal/MenuHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class MenuHalJsonAnonTest extends MenuResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Hal/MenuHalJsonBasicAuthTest.php b/core/modules/system/tests/src/Functional/Hal/MenuHalJsonBasicAuthTest.php
index cce118b1186b09935b50b66985ac07a5811a263d..3aaa10a0c91c11f47d632a88ecce3e0b3e0ec865 100644
--- a/core/modules/system/tests/src/Functional/Hal/MenuHalJsonBasicAuthTest.php
+++ b/core/modules/system/tests/src/Functional/Hal/MenuHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class MenuHalJsonBasicAuthTest extends MenuResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Hal/MenuHalJsonCookieTest.php b/core/modules/system/tests/src/Functional/Hal/MenuHalJsonCookieTest.php
index 9f7346f2592e47c499796ebac85028954d69f6ca..0d706f4585abe83ac2d85ea30d66cc162f746997 100644
--- a/core/modules/system/tests/src/Functional/Hal/MenuHalJsonCookieTest.php
+++ b/core/modules/system/tests/src/Functional/Hal/MenuHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class MenuHalJsonCookieTest extends MenuResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Lock/LockFunctionalTest.php b/core/modules/system/tests/src/Functional/Lock/LockFunctionalTest.php
index 0b13f18d6266ace1f22044686939a40202cbc221..766e81f7b7acac6fac10489a722686d4a62bbf47 100644
--- a/core/modules/system/tests/src/Functional/Lock/LockFunctionalTest.php
+++ b/core/modules/system/tests/src/Functional/Lock/LockFunctionalTest.php
@@ -18,6 +18,11 @@ class LockFunctionalTest extends BrowserTestBase {
    */
   public static $modules = ['system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Confirms that we can acquire and release locks in two parallel requests.
    */
diff --git a/core/modules/system/tests/src/Functional/Mail/HtmlToTextTest.php b/core/modules/system/tests/src/Functional/Mail/HtmlToTextTest.php
index 97092232d76e9ef6cce734f37913aaa70519f7f1..72b1fb2dd5d97c371bc02240e04fb8b536711fd6 100644
--- a/core/modules/system/tests/src/Functional/Mail/HtmlToTextTest.php
+++ b/core/modules/system/tests/src/Functional/Mail/HtmlToTextTest.php
@@ -14,6 +14,11 @@
  */
 class HtmlToTextTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Converts a string to its PHP source equivalent for display in test messages.
    *
diff --git a/core/modules/system/tests/src/Functional/Menu/BreadcrumbFrontCacheContextsTest.php b/core/modules/system/tests/src/Functional/Menu/BreadcrumbFrontCacheContextsTest.php
index 90272094672355c6b6246856b3b7e9dc64670ccf..2ede1c967398e601a836696d46e9f93cf3549b63 100644
--- a/core/modules/system/tests/src/Functional/Menu/BreadcrumbFrontCacheContextsTest.php
+++ b/core/modules/system/tests/src/Functional/Menu/BreadcrumbFrontCacheContextsTest.php
@@ -25,6 +25,11 @@ class BreadcrumbFrontCacheContextsTest extends BrowserTestBase {
     'user',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A test node with path alias.
    *
diff --git a/core/modules/system/tests/src/Functional/Menu/LocalActionTest.php b/core/modules/system/tests/src/Functional/Menu/LocalActionTest.php
index f7b9aafae40c6e73b1fa4b1cbd342b91748dd3c7..67875aa8d1c004021978355a06fa06570d627cda 100644
--- a/core/modules/system/tests/src/Functional/Menu/LocalActionTest.php
+++ b/core/modules/system/tests/src/Functional/Menu/LocalActionTest.php
@@ -20,6 +20,11 @@ class LocalActionTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'menu_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Menu/LocalTasksTest.php b/core/modules/system/tests/src/Functional/Menu/LocalTasksTest.php
index 0afc711624233c49d0e901232cd6c78f4c895529..59e9becdd5f500f4f9cdd29ec4330534fba9affe 100644
--- a/core/modules/system/tests/src/Functional/Menu/LocalTasksTest.php
+++ b/core/modules/system/tests/src/Functional/Menu/LocalTasksTest.php
@@ -21,6 +21,11 @@ class LocalTasksTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'menu_test', 'entity_test', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The local tasks block under testing.
    *
diff --git a/core/modules/system/tests/src/Functional/Menu/MenuAccessTest.php b/core/modules/system/tests/src/Functional/Menu/MenuAccessTest.php
index 7d3c0a4b3ddd5a2bfe89abf714d673c72caafd02..8c0b7ca498637f71c1b1f3f7913877cff2613847 100644
--- a/core/modules/system/tests/src/Functional/Menu/MenuAccessTest.php
+++ b/core/modules/system/tests/src/Functional/Menu/MenuAccessTest.php
@@ -19,6 +19,11 @@ class MenuAccessTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'menu_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Menu/MenuLinkSecurityTest.php b/core/modules/system/tests/src/Functional/Menu/MenuLinkSecurityTest.php
index c58bf8e504dc805deef52313d1c811d5ca6c64c8..d9433be31fa442138c9772c44015ae9324fd46d8 100644
--- a/core/modules/system/tests/src/Functional/Menu/MenuLinkSecurityTest.php
+++ b/core/modules/system/tests/src/Functional/Menu/MenuLinkSecurityTest.php
@@ -17,6 +17,11 @@ class MenuLinkSecurityTest extends BrowserTestBase {
    */
   public static $modules = ['menu_link_content', 'block', 'menu_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensures that a menu link does not cause an XSS issue.
    */
diff --git a/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php b/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php
index 882d92365af574105305cef0dcff8674fcdfacf6..f13707fff08c93df7ca3d4d677bfe302c27e6905 100644
--- a/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php
+++ b/core/modules/system/tests/src/Functional/Menu/MenuRouterTest.php
@@ -20,18 +20,16 @@ class MenuRouterTest extends BrowserTestBase {
   public static $modules = ['block', 'menu_test', 'test_page_test'];
 
   /**
-   * Name of the administrative theme to use for tests.
-   *
-   * @var string
+   * {@inheritdoc}
    */
-  protected $adminTheme;
+  protected $defaultTheme = 'stark';
 
   /**
-   * Name of the default theme to use for tests.
+   * Name of the administrative theme to use for tests.
    *
    * @var string
    */
-  protected $defaultTheme;
+  protected $adminTheme;
 
   protected function setUp() {
     // Enable dummy module that implements hook_menu.
diff --git a/core/modules/system/tests/src/Functional/Module/ClassLoaderTest.php b/core/modules/system/tests/src/Functional/Module/ClassLoaderTest.php
index 335a03a329b0f3d22064a24e71cedf22d95f4514..db82fe25f843466b136c2785c45321f31634be7d 100644
--- a/core/modules/system/tests/src/Functional/Module/ClassLoaderTest.php
+++ b/core/modules/system/tests/src/Functional/Module/ClassLoaderTest.php
@@ -23,6 +23,11 @@ class ClassLoaderTest extends BrowserTestBase {
    */
   protected $apcuEnsureUniquePrefix = TRUE;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that module-provided classes can be loaded when a module is enabled.
    *
diff --git a/core/modules/system/tests/src/Functional/Module/DependencyTest.php b/core/modules/system/tests/src/Functional/Module/DependencyTest.php
index adb8da9a56bd5c8fbeae7cc9fa93f6ea1b4ed81c..7d749f6020f1622578b9ddb80f7b0ed76eca5cae 100644
--- a/core/modules/system/tests/src/Functional/Module/DependencyTest.php
+++ b/core/modules/system/tests/src/Functional/Module/DependencyTest.php
@@ -11,6 +11,11 @@
  */
 class DependencyTest extends ModuleTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Checks functionality of project namespaces for dependencies.
    */
diff --git a/core/modules/system/tests/src/Functional/Module/ExperimentalModuleTest.php b/core/modules/system/tests/src/Functional/Module/ExperimentalModuleTest.php
index 177fc5ba1de81d4004159faa46ce117737de7962..eba632f0f9c60b87baaa4c24cca60cca793b6a79 100644
--- a/core/modules/system/tests/src/Functional/Module/ExperimentalModuleTest.php
+++ b/core/modules/system/tests/src/Functional/Module/ExperimentalModuleTest.php
@@ -19,6 +19,11 @@ class ExperimentalModuleTest extends BrowserTestBase {
    */
   protected $adminUser;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Module/HookRequirementsTest.php b/core/modules/system/tests/src/Functional/Module/HookRequirementsTest.php
index 2ada3a2854d939079edfe982d76d803011a5a859..317634b4d292388a104fc165fe386399b1651e28 100644
--- a/core/modules/system/tests/src/Functional/Module/HookRequirementsTest.php
+++ b/core/modules/system/tests/src/Functional/Module/HookRequirementsTest.php
@@ -9,6 +9,11 @@
  */
 class HookRequirementsTest extends ModuleTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Assert that a module cannot be installed if it fails hook_requirements().
    */
diff --git a/core/modules/system/tests/src/Functional/Module/InstallTest.php b/core/modules/system/tests/src/Functional/Module/InstallTest.php
index 43b66782f3a940934613105c3839a1d19d5b0833..08acec5b4cc223e1fc6091fbbd1bbbb4f12fcc10 100644
--- a/core/modules/system/tests/src/Functional/Module/InstallTest.php
+++ b/core/modules/system/tests/src/Functional/Module/InstallTest.php
@@ -21,6 +21,11 @@ class InstallTest extends BrowserTestBase {
    */
   public static $modules = ['module_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verify that drupal_get_schema() can be used during module installation.
    */
diff --git a/core/modules/system/tests/src/Functional/Module/InstallUninstallTest.php b/core/modules/system/tests/src/Functional/Module/InstallUninstallTest.php
index fd84c4db7ec1e76cb1a1db3d120a5770bc7b8d6d..31fb1b7931173a4be7973c56f903f4a95f6a88c2 100644
--- a/core/modules/system/tests/src/Functional/Module/InstallUninstallTest.php
+++ b/core/modules/system/tests/src/Functional/Module/InstallUninstallTest.php
@@ -14,6 +14,11 @@
  */
 class InstallUninstallTest extends ModuleTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Module/PrepareUninstallTest.php b/core/modules/system/tests/src/Functional/Module/PrepareUninstallTest.php
index 56e888d5c5f4fc1feed54f5a75804cef027a1486..fdabecdbec88193ea740a37e69d01a550699d615 100644
--- a/core/modules/system/tests/src/Functional/Module/PrepareUninstallTest.php
+++ b/core/modules/system/tests/src/Functional/Module/PrepareUninstallTest.php
@@ -14,6 +14,11 @@ class PrepareUninstallTest extends BrowserTestBase {
 
   use TaxonomyTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An array of node objects.
    *
diff --git a/core/modules/system/tests/src/Functional/Module/UninstallTest.php b/core/modules/system/tests/src/Functional/Module/UninstallTest.php
index d061646f7e9a91c5e592a68dbb97d926bb7b043f..c4202a4cdaf27dfac4ebbc151bf4b49d9fd118af 100644
--- a/core/modules/system/tests/src/Functional/Module/UninstallTest.php
+++ b/core/modules/system/tests/src/Functional/Module/UninstallTest.php
@@ -23,6 +23,11 @@ class UninstallTest extends BrowserTestBase {
    */
   public static $modules = ['module_test', 'user', 'views', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the hook_modules_uninstalled() of the user module.
    */
diff --git a/core/modules/system/tests/src/Functional/Module/VersionTest.php b/core/modules/system/tests/src/Functional/Module/VersionTest.php
index 7b325fef8f03edc915ff5df5c198ba1250d2b15c..2935edf2ac6281d5746380b019858f0d951252e7 100644
--- a/core/modules/system/tests/src/Functional/Module/VersionTest.php
+++ b/core/modules/system/tests/src/Functional/Module/VersionTest.php
@@ -9,6 +9,11 @@
  */
 class VersionTest extends ModuleTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test version dependencies.
    */
diff --git a/core/modules/system/tests/src/Functional/Page/DefaultMetatagsTest.php b/core/modules/system/tests/src/Functional/Page/DefaultMetatagsTest.php
index d020368c525b84e88b9f05b6cc52c10cae9433df..2493a38306df3b7498961d5a9ef63e16551f10ab 100644
--- a/core/modules/system/tests/src/Functional/Page/DefaultMetatagsTest.php
+++ b/core/modules/system/tests/src/Functional/Page/DefaultMetatagsTest.php
@@ -11,6 +11,11 @@
  */
 class DefaultMetatagsTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests meta tags.
    */
diff --git a/core/modules/system/tests/src/Functional/Pager/PagerTest.php b/core/modules/system/tests/src/Functional/Pager/PagerTest.php
index 7edbaa07757f7d06fc5c0dc3c181a606b620cb0d..7d30b145078ea4c13c51b1eb6b21a521b215e535 100644
--- a/core/modules/system/tests/src/Functional/Pager/PagerTest.php
+++ b/core/modules/system/tests/src/Functional/Pager/PagerTest.php
@@ -22,6 +22,11 @@ class PagerTest extends BrowserTestBase {
    */
   public static $modules = ['dblog', 'image', 'pager_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to access site reports.
    *
diff --git a/core/modules/system/tests/src/Functional/ParamConverter/UpcastingTest.php b/core/modules/system/tests/src/Functional/ParamConverter/UpcastingTest.php
index faafe84600ace73c8f31d1d733a3a2dd9a77144a..a0f3caff88ffa871586e1f42e270de18c072c9e7 100644
--- a/core/modules/system/tests/src/Functional/ParamConverter/UpcastingTest.php
+++ b/core/modules/system/tests/src/Functional/ParamConverter/UpcastingTest.php
@@ -14,6 +14,11 @@ class UpcastingTest extends BrowserTestBase {
 
   public static $modules = ['paramconverter_test', 'node', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Confirms that all parameters are converted as expected.
    *
diff --git a/core/modules/system/tests/src/Functional/Render/AjaxPageStateTest.php b/core/modules/system/tests/src/Functional/Render/AjaxPageStateTest.php
index 415a42881abb379ae2e18024c1dcd8deae430373..20c68695b857c62ae6a6f435f46f9d3733bfead6 100644
--- a/core/modules/system/tests/src/Functional/Render/AjaxPageStateTest.php
+++ b/core/modules/system/tests/src/Functional/Render/AjaxPageStateTest.php
@@ -18,6 +18,11 @@ class AjaxPageStateTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * User account with all available permissions
    *
diff --git a/core/modules/system/tests/src/Functional/Render/DisplayVariantTest.php b/core/modules/system/tests/src/Functional/Render/DisplayVariantTest.php
index 2f5415ba7c449280b1e5376929d89dcd245abee9..c10866acd16d12944b16442c2d5f0cdb66226dc4 100644
--- a/core/modules/system/tests/src/Functional/Render/DisplayVariantTest.php
+++ b/core/modules/system/tests/src/Functional/Render/DisplayVariantTest.php
@@ -18,6 +18,11 @@ class DisplayVariantTest extends BrowserTestBase {
    */
   public static $modules = ['display_variant_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests selecting the variant and passing configuration.
    */
diff --git a/core/modules/system/tests/src/Functional/Render/HtmlResponseAttachmentsTest.php b/core/modules/system/tests/src/Functional/Render/HtmlResponseAttachmentsTest.php
index 2bd6d289c6f807817e78c7587aa150e1076e3181..382a3442e79acd2937389d6bc7ac3e0d07a4d2b1 100644
--- a/core/modules/system/tests/src/Functional/Render/HtmlResponseAttachmentsTest.php
+++ b/core/modules/system/tests/src/Functional/Render/HtmlResponseAttachmentsTest.php
@@ -18,6 +18,11 @@ class HtmlResponseAttachmentsTest extends BrowserTestBase {
    */
   public static $modules = ['render_attached_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test rendering of ['#attached'].
    */
diff --git a/core/modules/system/tests/src/Functional/Render/PlaceholderMessageTest.php b/core/modules/system/tests/src/Functional/Render/PlaceholderMessageTest.php
index 185ca4985a0cae76861b8a22b88b6de1702cec23..97ca6d22d2acee5be5f606cddcb6a47c05cc3e94 100644
--- a/core/modules/system/tests/src/Functional/Render/PlaceholderMessageTest.php
+++ b/core/modules/system/tests/src/Functional/Render/PlaceholderMessageTest.php
@@ -19,6 +19,11 @@ class PlaceholderMessageTest extends BrowserTestBase {
    */
   public static $modules = ['render_placeholder_message_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test rendering of message placeholder.
    */
diff --git a/core/modules/system/tests/src/Functional/Render/RenderArrayNonHtmlSubscriberTest.php b/core/modules/system/tests/src/Functional/Render/RenderArrayNonHtmlSubscriberTest.php
index 08380dec024e909a13bd64928e50062b7307748a..4f02d1a7c911800108797ccadd917d3e6a9b2898 100644
--- a/core/modules/system/tests/src/Functional/Render/RenderArrayNonHtmlSubscriberTest.php
+++ b/core/modules/system/tests/src/Functional/Render/RenderArrayNonHtmlSubscriberTest.php
@@ -19,6 +19,11 @@ class RenderArrayNonHtmlSubscriberTest extends BrowserTestBase {
    */
   public static $modules = ['render_array_non_html_subscriber_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests handling of responses by events subscriber.
    */
diff --git a/core/modules/system/tests/src/Functional/Render/UrlBubbleableMetadataBubblingTest.php b/core/modules/system/tests/src/Functional/Render/UrlBubbleableMetadataBubblingTest.php
index 37d20ce3b83a03043820f27ccbf90bf6228bbe99..4c25fceeb836398ecee8d66f4d400063f063e763 100644
--- a/core/modules/system/tests/src/Functional/Render/UrlBubbleableMetadataBubblingTest.php
+++ b/core/modules/system/tests/src/Functional/Render/UrlBubbleableMetadataBubblingTest.php
@@ -22,6 +22,11 @@ class UrlBubbleableMetadataBubblingTest extends BrowserTestBase {
    */
   public static $modules = ['cache_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Rest/ActionJsonAnonTest.php b/core/modules/system/tests/src/Functional/Rest/ActionJsonAnonTest.php
index 07a7a5b3dd58ce5ea08adb0c577e5b7f462eea70..a3da1f60399df0b528a360a9fb84f5bfae3f6ef0 100644
--- a/core/modules/system/tests/src/Functional/Rest/ActionJsonAnonTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/ActionJsonAnonTest.php
@@ -21,4 +21,9 @@ class ActionJsonAnonTest extends ActionResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Rest/ActionJsonBasicAuthTest.php b/core/modules/system/tests/src/Functional/Rest/ActionJsonBasicAuthTest.php
index fdc516b9e4abbbea52ade55bbdd5d89728b1fc49..98c1d9a2a85701081bb0f0f2026cf782bceb093e 100644
--- a/core/modules/system/tests/src/Functional/Rest/ActionJsonBasicAuthTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/ActionJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ActionJsonBasicAuthTest extends ActionResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Rest/ActionJsonCookieTest.php b/core/modules/system/tests/src/Functional/Rest/ActionJsonCookieTest.php
index 0766f03f080c5b4ccc659a788de41f0311d5baaa..82194e8670a01a74bd814b13b9718a9ca7b77363 100644
--- a/core/modules/system/tests/src/Functional/Rest/ActionJsonCookieTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/ActionJsonCookieTest.php
@@ -26,4 +26,9 @@ class ActionJsonCookieTest extends ActionResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Rest/ActionXmlAnonTest.php b/core/modules/system/tests/src/Functional/Rest/ActionXmlAnonTest.php
index e45af980ea1280fc245a5192e9f99052d4c90461..db0e28ab0b5ef76f309b9536ec17796b924f05ef 100644
--- a/core/modules/system/tests/src/Functional/Rest/ActionXmlAnonTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/ActionXmlAnonTest.php
@@ -23,4 +23,9 @@ class ActionXmlAnonTest extends ActionResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Rest/ActionXmlBasicAuthTest.php b/core/modules/system/tests/src/Functional/Rest/ActionXmlBasicAuthTest.php
index f11459bc6d0eaed0aa02615ef67768a35dce9a22..0e90dbea31216cfac8f44723bf126cfd41e1965f 100644
--- a/core/modules/system/tests/src/Functional/Rest/ActionXmlBasicAuthTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/ActionXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ActionXmlBasicAuthTest extends ActionResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Rest/ActionXmlCookieTest.php b/core/modules/system/tests/src/Functional/Rest/ActionXmlCookieTest.php
index dbee6fa1af3b6860f330a04a15025442a4b5b788..71c703c27c1b1265773d6c681ade2d9d53ca3cfa 100644
--- a/core/modules/system/tests/src/Functional/Rest/ActionXmlCookieTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/ActionXmlCookieTest.php
@@ -28,4 +28,9 @@ class ActionXmlCookieTest extends ActionResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Rest/MenuJsonAnonTest.php b/core/modules/system/tests/src/Functional/Rest/MenuJsonAnonTest.php
index 468deb5178e053f9c2f7c11a1affc6ef8aba777b..fbd61d7e83e787935d89a59fd47781829e0ec2dc 100644
--- a/core/modules/system/tests/src/Functional/Rest/MenuJsonAnonTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/MenuJsonAnonTest.php
@@ -21,4 +21,9 @@ class MenuJsonAnonTest extends MenuResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Rest/MenuJsonBasicAuthTest.php b/core/modules/system/tests/src/Functional/Rest/MenuJsonBasicAuthTest.php
index 1d35d421619d1ef679c55f8609d321a1927a1ca0..5b9fe9e3bc0614ff2a72003f1d0c254f695ee0a0 100644
--- a/core/modules/system/tests/src/Functional/Rest/MenuJsonBasicAuthTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/MenuJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class MenuJsonBasicAuthTest extends MenuResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Rest/MenuJsonCookieTest.php b/core/modules/system/tests/src/Functional/Rest/MenuJsonCookieTest.php
index d923875e1531e0717a2b88f6d2b449e0889f0fbc..85c880028e2c80413525dfda3a5c003bd192f402 100644
--- a/core/modules/system/tests/src/Functional/Rest/MenuJsonCookieTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/MenuJsonCookieTest.php
@@ -26,4 +26,9 @@ class MenuJsonCookieTest extends MenuResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Rest/MenuXmlAnonTest.php b/core/modules/system/tests/src/Functional/Rest/MenuXmlAnonTest.php
index e1c23b5f70f6646917a082f81f1cc8e74842a6fc..cf9d2101f7347cbeac85d0016ea404003f804fc2 100644
--- a/core/modules/system/tests/src/Functional/Rest/MenuXmlAnonTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/MenuXmlAnonTest.php
@@ -23,4 +23,9 @@ class MenuXmlAnonTest extends MenuResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Rest/MenuXmlBasicAuthTest.php b/core/modules/system/tests/src/Functional/Rest/MenuXmlBasicAuthTest.php
index 0910430042856e1f892f0f3d5cbba8b15bef76eb..9f786dd4de4bdcdd2af31c5def1de6a89b5c4e63 100644
--- a/core/modules/system/tests/src/Functional/Rest/MenuXmlBasicAuthTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/MenuXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class MenuXmlBasicAuthTest extends MenuResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Rest/MenuXmlCookieTest.php b/core/modules/system/tests/src/Functional/Rest/MenuXmlCookieTest.php
index a229b6a3b27821f208d2c907d8e4bb35f9102665..45f6a79699ee930be5644c999cd7018d82cbe6d3 100644
--- a/core/modules/system/tests/src/Functional/Rest/MenuXmlCookieTest.php
+++ b/core/modules/system/tests/src/Functional/Rest/MenuXmlCookieTest.php
@@ -28,4 +28,9 @@ class MenuXmlCookieTest extends MenuResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/system/tests/src/Functional/Routing/DestinationTest.php b/core/modules/system/tests/src/Functional/Routing/DestinationTest.php
index 109d8000074d954fad337b36b107bb6b585446c7..98ec29b4731221a2a0057a706c0315922dbfed65 100644
--- a/core/modules/system/tests/src/Functional/Routing/DestinationTest.php
+++ b/core/modules/system/tests/src/Functional/Routing/DestinationTest.php
@@ -22,6 +22,11 @@ class DestinationTest extends BrowserTestBase {
    */
   public static $modules = ['system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that $_GET/$_REQUEST['destination'] only contain internal URLs.
    */
diff --git a/core/modules/system/tests/src/Functional/Routing/RouterPermissionTest.php b/core/modules/system/tests/src/Functional/Routing/RouterPermissionTest.php
index 62a511f2e438101d4f60109bc2f2e64c24fce4d7..1985725ef3560c19ff7a15d21b6dc67045ba1abb 100644
--- a/core/modules/system/tests/src/Functional/Routing/RouterPermissionTest.php
+++ b/core/modules/system/tests/src/Functional/Routing/RouterPermissionTest.php
@@ -18,6 +18,11 @@ class RouterPermissionTest extends BrowserTestBase {
    */
   public static $modules = ['router_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests permission requirements on routes.
    */
diff --git a/core/modules/system/tests/src/Functional/Routing/RouterTest.php b/core/modules/system/tests/src/Functional/Routing/RouterTest.php
index 47361411b98154a968c95fa241e7024c464f3084..974afee8651c3997c6bc9dd81dadca6569919100 100644
--- a/core/modules/system/tests/src/Functional/Routing/RouterTest.php
+++ b/core/modules/system/tests/src/Functional/Routing/RouterTest.php
@@ -23,6 +23,11 @@ class RouterTest extends BrowserTestBase {
    */
   public static $modules = ['router_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Confirms that our FinishResponseSubscriber logic works properly.
    */
diff --git a/core/modules/system/tests/src/Functional/ServiceProvider/ServiceProviderWebTest.php b/core/modules/system/tests/src/Functional/ServiceProvider/ServiceProviderWebTest.php
index 5e86164f6e6dc2504bac02d91034315b4a9a0d17..773c1795ecdf25ec74832192229cb2d754d89e31 100644
--- a/core/modules/system/tests/src/Functional/ServiceProvider/ServiceProviderWebTest.php
+++ b/core/modules/system/tests/src/Functional/ServiceProvider/ServiceProviderWebTest.php
@@ -18,6 +18,11 @@ class ServiceProviderWebTest extends BrowserTestBase {
    */
   public static $modules = ['file', 'service_provider_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that module service providers get registered to the DIC.
    *
diff --git a/core/modules/system/tests/src/Functional/Session/SessionAuthenticationTest.php b/core/modules/system/tests/src/Functional/Session/SessionAuthenticationTest.php
index 7825877686f0c92ffa9b8ab4576f284364d3b3a2..702486d99e4023636cf7e5aa3bf72d58581372d3 100644
--- a/core/modules/system/tests/src/Functional/Session/SessionAuthenticationTest.php
+++ b/core/modules/system/tests/src/Functional/Session/SessionAuthenticationTest.php
@@ -27,6 +27,11 @@ class SessionAuthenticationTest extends BrowserTestBase {
    */
   public static $modules = ['basic_auth', 'session_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php b/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php
index 13292b4d6151465726d8af0fe8446298599124b2..dbdbe664cea537933ae6df0423deac969e42d7b0 100644
--- a/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php
+++ b/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php
@@ -38,6 +38,11 @@ class SessionHttpsTest extends BrowserTestBase {
    */
   public static $modules = ['session_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Session/SessionTest.php b/core/modules/system/tests/src/Functional/Session/SessionTest.php
index 0822fe435c46e3c894109682b2632195db32d31f..7141ba45394d3484f73e3dfe6e49466795226e47 100644
--- a/core/modules/system/tests/src/Functional/Session/SessionTest.php
+++ b/core/modules/system/tests/src/Functional/Session/SessionTest.php
@@ -20,6 +20,11 @@ class SessionTest extends BrowserTestBase {
    */
   public static $modules = ['session_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $dumpHeaders = TRUE;
 
   /**
diff --git a/core/modules/system/tests/src/Functional/Session/StackSessionHandlerIntegrationTest.php b/core/modules/system/tests/src/Functional/Session/StackSessionHandlerIntegrationTest.php
index d65ba4216044fa6e63b262d4df6fce8f9de683b0..9b71436175cf366a2d51c1df2eff347609172c9b 100644
--- a/core/modules/system/tests/src/Functional/Session/StackSessionHandlerIntegrationTest.php
+++ b/core/modules/system/tests/src/Functional/Session/StackSessionHandlerIntegrationTest.php
@@ -17,6 +17,11 @@ class StackSessionHandlerIntegrationTest extends BrowserTestBase {
    */
   protected static $modules = ['session_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests a request.
    */
diff --git a/core/modules/system/tests/src/Functional/System/AccessDeniedTest.php b/core/modules/system/tests/src/Functional/System/AccessDeniedTest.php
index c0749b490caac9373764c66039eaae17111efef3..4c4b0cb1c5c4edafdd55b6be75c66f7493d4c313 100644
--- a/core/modules/system/tests/src/Functional/System/AccessDeniedTest.php
+++ b/core/modules/system/tests/src/Functional/System/AccessDeniedTest.php
@@ -23,6 +23,11 @@ class AccessDeniedTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'node', 'system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $adminUser;
 
   protected function setUp() {
diff --git a/core/modules/system/tests/src/Functional/System/AdminMetaTagTest.php b/core/modules/system/tests/src/Functional/System/AdminMetaTagTest.php
index 6fcc4b848d1850c8ca515402c76064cd61cc776a..d17e537b679ca47cf3ca678d0e1966d8bf54defa 100644
--- a/core/modules/system/tests/src/Functional/System/AdminMetaTagTest.php
+++ b/core/modules/system/tests/src/Functional/System/AdminMetaTagTest.php
@@ -11,6 +11,11 @@
  */
 class AdminMetaTagTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verify that the meta tag HTML is generated correctly.
    */
diff --git a/core/modules/system/tests/src/Functional/System/AdminTest.php b/core/modules/system/tests/src/Functional/System/AdminTest.php
index 7a0b2a3ae6c1af086b8435d9356db6b050f3eb15..a80651951245a001806ecc97f76ac8bc43c506b8 100644
--- a/core/modules/system/tests/src/Functional/System/AdminTest.php
+++ b/core/modules/system/tests/src/Functional/System/AdminTest.php
@@ -33,6 +33,11 @@ class AdminTest extends BrowserTestBase {
    */
   public static $modules = ['locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     // testAdminPages() requires Locale module.
     parent::setUp();
diff --git a/core/modules/system/tests/src/Functional/System/CronRunTest.php b/core/modules/system/tests/src/Functional/System/CronRunTest.php
index 12b86c83e7edbf2acc7b1b9d22a4a392bd9b937f..eecd9db7f705ae49efa599c41e2e92d3b5fd8978 100644
--- a/core/modules/system/tests/src/Functional/System/CronRunTest.php
+++ b/core/modules/system/tests/src/Functional/System/CronRunTest.php
@@ -21,6 +21,11 @@ class CronRunTest extends BrowserTestBase {
    */
   public static $modules = ['common_test', 'common_test_cron_helper', 'automated_cron'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test cron runs.
    */
diff --git a/core/modules/system/tests/src/Functional/System/DateFormatsLockedTest.php b/core/modules/system/tests/src/Functional/System/DateFormatsLockedTest.php
index faac2b76277f064e5bbe480a7628ba6a23f875fe..d09d8d13480362eeca2eb84a1ee6da539f65d030 100644
--- a/core/modules/system/tests/src/Functional/System/DateFormatsLockedTest.php
+++ b/core/modules/system/tests/src/Functional/System/DateFormatsLockedTest.php
@@ -11,6 +11,11 @@
  */
 class DateFormatsLockedTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests attempts at listing, editing, and deleting locked date formats.
    */
diff --git a/core/modules/system/tests/src/Functional/System/DateFormatsMachineNameTest.php b/core/modules/system/tests/src/Functional/System/DateFormatsMachineNameTest.php
index fd88bdc77fd2ff9d29ced686b8f04c98fadb1ff2..606a287a20bc84b3785187f22fee57577d8e87f3 100644
--- a/core/modules/system/tests/src/Functional/System/DateFormatsMachineNameTest.php
+++ b/core/modules/system/tests/src/Functional/System/DateFormatsMachineNameTest.php
@@ -11,6 +11,11 @@
  */
 class DateFormatsMachineNameTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/System/DateTimeTest.php b/core/modules/system/tests/src/Functional/System/DateTimeTest.php
index 0a365a7a7dab75195c5bb34018b0f347c552473b..0ecebb433a65dd9baa1a8813f7feccc153610e64 100644
--- a/core/modules/system/tests/src/Functional/System/DateTimeTest.php
+++ b/core/modules/system/tests/src/Functional/System/DateTimeTest.php
@@ -21,6 +21,11 @@ class DateTimeTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'node', 'language', 'field', 'field_ui', 'datetime', 'options'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/system/tests/src/Functional/System/DefaultMobileMetaTagsTest.php b/core/modules/system/tests/src/Functional/System/DefaultMobileMetaTagsTest.php
index 922839f9953927f8ec4f4da5ebb90b9ab704c992..a8f54bad60be0c66ab28e9abed114e367a67e1ff 100644
--- a/core/modules/system/tests/src/Functional/System/DefaultMobileMetaTagsTest.php
+++ b/core/modules/system/tests/src/Functional/System/DefaultMobileMetaTagsTest.php
@@ -19,6 +19,11 @@ class DefaultMobileMetaTagsTest extends BrowserTestBase {
    */
   protected $defaultMetaTags;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->defaultMetaTags = [
diff --git a/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php b/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php
index 7290537441486d02e5353add5dc233091dec3e51..5b4a7d17486a8630ca286996dba3651bdf45eb15 100644
--- a/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php
+++ b/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php
@@ -19,6 +19,11 @@ class ErrorHandlerTest extends BrowserTestBase {
    */
   public static $modules = ['error_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test the error handler.
    */
diff --git a/core/modules/system/tests/src/Functional/System/FrontPageTest.php b/core/modules/system/tests/src/Functional/System/FrontPageTest.php
index 7f9fc8c1f0711623dafcfe8cbfcd530fc97a7ed3..98bab99adee90ad8873921b360df7d3baa6926dd 100644
--- a/core/modules/system/tests/src/Functional/System/FrontPageTest.php
+++ b/core/modules/system/tests/src/Functional/System/FrontPageTest.php
@@ -19,6 +19,11 @@ class FrontPageTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'system_test', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The path to a node that is created for testing.
    *
diff --git a/core/modules/system/tests/src/Functional/System/HtaccessTest.php b/core/modules/system/tests/src/Functional/System/HtaccessTest.php
index 7d8ea086ed685f2df44e0cd499235d8967276037..037a92a00fe39544a4982eac9118f855c7a04fb0 100644
--- a/core/modules/system/tests/src/Functional/System/HtaccessTest.php
+++ b/core/modules/system/tests/src/Functional/System/HtaccessTest.php
@@ -18,6 +18,11 @@ class HtaccessTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'path'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Get an array of file paths for access testing.
    *
diff --git a/core/modules/system/tests/src/Functional/System/IndexPhpTest.php b/core/modules/system/tests/src/Functional/System/IndexPhpTest.php
index 4675fed0faa0ded7e872a7b1507e048ab99887a5..4146d0c655cf3cf48af0dddf78a70fbd0e164ac6 100644
--- a/core/modules/system/tests/src/Functional/System/IndexPhpTest.php
+++ b/core/modules/system/tests/src/Functional/System/IndexPhpTest.php
@@ -11,6 +11,11 @@
  */
 class IndexPhpTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
   }
diff --git a/core/modules/system/tests/src/Functional/System/MainContentFallbackTest.php b/core/modules/system/tests/src/Functional/System/MainContentFallbackTest.php
index 931b84ce2422a2ef6d7aa9870319596bcf8a96c2..acbb60aa8bdaed209bd279b72376feea66bdc1a7 100644
--- a/core/modules/system/tests/src/Functional/System/MainContentFallbackTest.php
+++ b/core/modules/system/tests/src/Functional/System/MainContentFallbackTest.php
@@ -18,6 +18,11 @@ class MainContentFallbackTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $adminUser;
   protected $webUser;
 
diff --git a/core/modules/system/tests/src/Functional/System/PageNotFoundTest.php b/core/modules/system/tests/src/Functional/System/PageNotFoundTest.php
index 060f53aa1966fad8d2c49caab690ab404bc526d4..45522da9bd39a16f68f3c7f809ec1d4a93e84257 100644
--- a/core/modules/system/tests/src/Functional/System/PageNotFoundTest.php
+++ b/core/modules/system/tests/src/Functional/System/PageNotFoundTest.php
@@ -23,6 +23,11 @@ class PageNotFoundTest extends BrowserTestBase {
    */
   public static $modules = ['system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $adminUser;
 
   protected function setUp() {
diff --git a/core/modules/system/tests/src/Functional/System/PageTitleTest.php b/core/modules/system/tests/src/Functional/System/PageTitleTest.php
index 8073827fb271a9f51aae8e5ed24d4d1df11b99c2..bc2ed2018824aa5c237f5e2cfa8bb84fd25fe60f 100644
--- a/core/modules/system/tests/src/Functional/System/PageTitleTest.php
+++ b/core/modules/system/tests/src/Functional/System/PageTitleTest.php
@@ -21,6 +21,11 @@ class PageTitleTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'test_page_test', 'form_test', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected $contentUser;
   protected $savedTitle;
 
diff --git a/core/modules/system/tests/src/Functional/System/ResponseGeneratorTest.php b/core/modules/system/tests/src/Functional/System/ResponseGeneratorTest.php
index d0f2ab539a43a5f549041c0e2b4f7bb107fa41ef..5c8f547c4d57f67fedc70f572d15fe4fa1586ee5 100644
--- a/core/modules/system/tests/src/Functional/System/ResponseGeneratorTest.php
+++ b/core/modules/system/tests/src/Functional/System/ResponseGeneratorTest.php
@@ -19,6 +19,11 @@ class ResponseGeneratorTest extends BrowserTestBase {
    */
   public static $modules = ['hal', 'rest', 'node', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/System/RetrieveFileTest.php b/core/modules/system/tests/src/Functional/System/RetrieveFileTest.php
index bcd8f7d3bfb3f72c68bbe9cea76c3c1e9debf3de..25db399666f2a21877b7915a23c460b150883ae1 100644
--- a/core/modules/system/tests/src/Functional/System/RetrieveFileTest.php
+++ b/core/modules/system/tests/src/Functional/System/RetrieveFileTest.php
@@ -11,6 +11,11 @@
  */
 class RetrieveFileTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Invokes system_retrieve_file() in several scenarios.
    */
diff --git a/core/modules/system/tests/src/Functional/System/ShutdownFunctionsTest.php b/core/modules/system/tests/src/Functional/System/ShutdownFunctionsTest.php
index f5d55be7822a04f9b79fa21c1a420abc8a6f30ad..c7e25bedaf508ba807031f8f94b5145a5fe8dba1 100644
--- a/core/modules/system/tests/src/Functional/System/ShutdownFunctionsTest.php
+++ b/core/modules/system/tests/src/Functional/System/ShutdownFunctionsTest.php
@@ -18,6 +18,11 @@ class ShutdownFunctionsTest extends BrowserTestBase {
    */
   public static $modules = ['system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function tearDown() {
     // This test intentionally throws an exception in a PHP shutdown function.
     // Prevent it from being interpreted as an actual test failure.
diff --git a/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php b/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php
index 8d2e42d870a5057aaa803e2a8851821e76d47a81..ec3a4b69500250bc83d1070543d4101f3b24b837 100644
--- a/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php
+++ b/core/modules/system/tests/src/Functional/System/SiteMaintenanceTest.php
@@ -24,6 +24,11 @@ class SiteMaintenanceTest extends BrowserTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $adminUser;
 
   protected function setUp() {
diff --git a/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php b/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php
index f08a18d8bc4158445eb30e90708857d51553dd99..ce3ac2a835ab7c3caeed7a15eb2a9602b99ea68c 100644
--- a/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php
+++ b/core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php
@@ -15,6 +15,11 @@
 class SitesDirectoryHardeningTest extends BrowserTestBase {
   use StringTranslationTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the default behavior to restrict directory permissions is enforced.
    *
diff --git a/core/modules/system/tests/src/Functional/System/StatusTest.php b/core/modules/system/tests/src/Functional/System/StatusTest.php
index 845b5a8e92e0ca643d000f21d3b37784c4bc8f13..6d4cce4c7b0f8fa7e169369737166ad8506a86dc 100644
--- a/core/modules/system/tests/src/Functional/System/StatusTest.php
+++ b/core/modules/system/tests/src/Functional/System/StatusTest.php
@@ -18,6 +18,11 @@ class StatusTest extends BrowserTestBase {
    */
   public static $modules = ['update_test_postupdate'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/System/SystemAuthorizeTest.php b/core/modules/system/tests/src/Functional/System/SystemAuthorizeTest.php
index b3f9b310b385dc0d5e5807b677ec80a2362d1d1b..36f7208ea75700080447da2d64679dd2d63d0602 100644
--- a/core/modules/system/tests/src/Functional/System/SystemAuthorizeTest.php
+++ b/core/modules/system/tests/src/Functional/System/SystemAuthorizeTest.php
@@ -18,6 +18,11 @@ class SystemAuthorizeTest extends BrowserTestBase {
    */
   public static $modules = ['system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/system/tests/src/Functional/System/ThemeTest.php b/core/modules/system/tests/src/Functional/System/ThemeTest.php
index 2fa4d917bd5e8c41ce94ce51a6a0a3046d6dad76..2a7b5f898cd88d5179730b8458870bf3583a7f2c 100644
--- a/core/modules/system/tests/src/Functional/System/ThemeTest.php
+++ b/core/modules/system/tests/src/Functional/System/ThemeTest.php
@@ -33,6 +33,11 @@ class ThemeTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'block', 'file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/system/tests/src/Functional/System/TokenReplaceWebTest.php b/core/modules/system/tests/src/Functional/System/TokenReplaceWebTest.php
index 450f50704552c9a9084e4d953444e949d08fa136..de6edc66c00416b670f224c491b2c6fcb4439903 100644
--- a/core/modules/system/tests/src/Functional/System/TokenReplaceWebTest.php
+++ b/core/modules/system/tests/src/Functional/System/TokenReplaceWebTest.php
@@ -20,6 +20,11 @@ class TokenReplaceWebTest extends BrowserTestBase {
    */
   public static $modules = ['token_test', 'filter', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests a token replacement on an actual website.
    */
diff --git a/core/modules/system/tests/src/Functional/System/TokenScanTest.php b/core/modules/system/tests/src/Functional/System/TokenScanTest.php
index f284aa978b4e88e4405bcdf0cc0c1a23432942e9..77e28d6edeb7a1144ecb6ece44836f3740fc1675 100644
--- a/core/modules/system/tests/src/Functional/System/TokenScanTest.php
+++ b/core/modules/system/tests/src/Functional/System/TokenScanTest.php
@@ -11,6 +11,11 @@
  */
 class TokenScanTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Scans dummy text, then tests the output.
    */
diff --git a/core/modules/system/tests/src/Functional/System/TrustedHostsTest.php b/core/modules/system/tests/src/Functional/System/TrustedHostsTest.php
index 8114ff4d4a31b65fb682dd3d806ec411ecac8eb0..13f43b80b2e12420e8472e2384eb34b6e14169d6 100644
--- a/core/modules/system/tests/src/Functional/System/TrustedHostsTest.php
+++ b/core/modules/system/tests/src/Functional/System/TrustedHostsTest.php
@@ -11,6 +11,11 @@
  */
 class TrustedHostsTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/EngineNyanCatTest.php b/core/modules/system/tests/src/Functional/Theme/EngineNyanCatTest.php
index 368e1276c7cfcb4fb7ddc1d1e632bd025638c238..d2b5e3212014b5106c9e4e52302695243b3350b1 100644
--- a/core/modules/system/tests/src/Functional/Theme/EngineNyanCatTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/EngineNyanCatTest.php
@@ -18,6 +18,11 @@ class EngineNyanCatTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     \Drupal::service('theme_installer')->install(['test_theme_nyan_cat_engine']);
diff --git a/core/modules/system/tests/src/Functional/Theme/EngineTwigTest.php b/core/modules/system/tests/src/Functional/Theme/EngineTwigTest.php
index c832b2934c77c2e257f5448fdaa5fcb33cbd9d38..756e8076dfa5ebde6e58c8ed064f9f8c532a0657 100644
--- a/core/modules/system/tests/src/Functional/Theme/EngineTwigTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/EngineTwigTest.php
@@ -23,6 +23,11 @@ class EngineTwigTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test', 'twig_theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     \Drupal::service('theme_installer')->install(['test_theme']);
diff --git a/core/modules/system/tests/src/Functional/Theme/EntityFilteringThemeTest.php b/core/modules/system/tests/src/Functional/Theme/EntityFilteringThemeTest.php
index a921e873434ae09114c9a25e8264b9e44f30141c..f79f990de24505b3485009589c0d46dbea6e5ac4 100644
--- a/core/modules/system/tests/src/Functional/Theme/EntityFilteringThemeTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/EntityFilteringThemeTest.php
@@ -21,6 +21,11 @@ class EntityFilteringThemeTest extends BrowserTestBase {
 
   use CommentTestTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Use the standard profile.
    *
diff --git a/core/modules/system/tests/src/Functional/Theme/ExperimentalThemeTest.php b/core/modules/system/tests/src/Functional/Theme/ExperimentalThemeTest.php
index be37f4a23c32254ff24d0ec03d44bf5744f39653..01409642f53f6b4e3d51eeffada1e3b026bf0edd 100644
--- a/core/modules/system/tests/src/Functional/Theme/ExperimentalThemeTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ExperimentalThemeTest.php
@@ -18,6 +18,11 @@ class ExperimentalThemeTest extends BrowserTestBase {
    */
   protected $adminUser;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/FastTest.php b/core/modules/system/tests/src/Functional/Theme/FastTest.php
index 977f54dfcedba30e4085eb63b705f7284fbd3827..80012487b89bbc2757b07a0c579de48c4b5ea658 100644
--- a/core/modules/system/tests/src/Functional/Theme/FastTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/FastTest.php
@@ -18,6 +18,11 @@ class FastTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->account = $this->drupalCreateUser(['access user profiles']);
diff --git a/core/modules/system/tests/src/Functional/Theme/HtmlAttributesTest.php b/core/modules/system/tests/src/Functional/Theme/HtmlAttributesTest.php
index 5aa4be9cc9d3e7e0bba828043e04f2af02fa8dbb..fccf2ff4d63cd853d8a511780a2b2be3411bd714 100644
--- a/core/modules/system/tests/src/Functional/Theme/HtmlAttributesTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/HtmlAttributesTest.php
@@ -18,6 +18,11 @@ class HtmlAttributesTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that attributes in the 'html' and 'body' elements can be altered.
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/ThemeEarlyInitializationTest.php b/core/modules/system/tests/src/Functional/Theme/ThemeEarlyInitializationTest.php
index 040dfabfce91fee3b72b65db8e52ab431aebaacb..13d09e63e73419bd4c9f2b82cff35330c99a90ae 100644
--- a/core/modules/system/tests/src/Functional/Theme/ThemeEarlyInitializationTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ThemeEarlyInitializationTest.php
@@ -19,6 +19,11 @@ class ThemeEarlyInitializationTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Test that the theme system can generate output in a request listener.
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/ThemeInfoTest.php b/core/modules/system/tests/src/Functional/Theme/ThemeInfoTest.php
index 8d972c045a1e82a727f38021fcda805e791f6af1..05fbca78b02fa7646603d70f8f0156ef3c83f828 100644
--- a/core/modules/system/tests/src/Functional/Theme/ThemeInfoTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ThemeInfoTest.php
@@ -18,6 +18,11 @@ class ThemeInfoTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The theme installer used in this test for enabling themes.
    *
diff --git a/core/modules/system/tests/src/Functional/Theme/ThemeSuggestionsAlterTest.php b/core/modules/system/tests/src/Functional/Theme/ThemeSuggestionsAlterTest.php
index cac5e31c1fb45ef17d023015ed461fced5d0360d..c521f58e50f79efe595f4a534259beae115f035e 100644
--- a/core/modules/system/tests/src/Functional/Theme/ThemeSuggestionsAlterTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ThemeSuggestionsAlterTest.php
@@ -19,6 +19,11 @@ class ThemeSuggestionsAlterTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     \Drupal::service('theme_installer')->install(['test_theme']);
diff --git a/core/modules/system/tests/src/Functional/Theme/ThemeTest.php b/core/modules/system/tests/src/Functional/Theme/ThemeTest.php
index 019077de55c1a756325349250f7d5366455afbca..fe4471a2fa28fc9514dbec7e62751fd2d8fafa6c 100644
--- a/core/modules/system/tests/src/Functional/Theme/ThemeTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ThemeTest.php
@@ -20,6 +20,11 @@ class ThemeTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php b/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php
index a399bed73d967f7354c37070d835ddb02ff49793..c1d8f37d984288b54bca09113eea810ce40f4062 100644
--- a/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/ThemeTokenTest.php
@@ -18,6 +18,11 @@ class ThemeTokenTest extends BrowserTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/TwigDebugMarkupTest.php b/core/modules/system/tests/src/Functional/Theme/TwigDebugMarkupTest.php
index e67a6341be584d43629bbe0698779ffa9f9ed0d1..90e5cf842a93097c69eb3dffeff45fe34a7f02ea 100644
--- a/core/modules/system/tests/src/Functional/Theme/TwigDebugMarkupTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/TwigDebugMarkupTest.php
@@ -19,6 +19,11 @@ class TwigDebugMarkupTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests debug markup added to Twig template output.
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/TwigEnvironmentTest.php b/core/modules/system/tests/src/Functional/Theme/TwigEnvironmentTest.php
index 26f47e9068eb3c1fbd25949c43cfba2e327b211d..1043148fd4722dd60d7e63a1c84c3c3b0f8a590d 100644
--- a/core/modules/system/tests/src/Functional/Theme/TwigEnvironmentTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/TwigEnvironmentTest.php
@@ -16,6 +16,11 @@ class TwigEnvironmentTest extends BrowserTestBase {
    */
   protected static $modules = ['twig_theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests template class loading with Twig embed.
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/TwigExtensionTest.php b/core/modules/system/tests/src/Functional/Theme/TwigExtensionTest.php
index 3966d6843a453f2a4e520517148cc5538900668d..04e527e74b9e38b5ce2fa4d451adf190db0217d6 100644
--- a/core/modules/system/tests/src/Functional/Theme/TwigExtensionTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/TwigExtensionTest.php
@@ -19,6 +19,11 @@ class TwigExtensionTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test', 'twig_extension_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     \Drupal::service('theme_installer')->install(['test_theme']);
diff --git a/core/modules/system/tests/src/Functional/Theme/TwigLoaderTest.php b/core/modules/system/tests/src/Functional/Theme/TwigLoaderTest.php
index d2b0b5465d2de5cba354f672aa04e0c260d857b7..1238f2074ace4100565208efde25130c4f7a205d 100644
--- a/core/modules/system/tests/src/Functional/Theme/TwigLoaderTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/TwigLoaderTest.php
@@ -18,6 +18,11 @@ class TwigLoaderTest extends BrowserTestBase {
    */
   public static $modules = ['twig_loader_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests adding an additional twig loader to the loader chain.
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/TwigRegistryLoaderTest.php b/core/modules/system/tests/src/Functional/Theme/TwigRegistryLoaderTest.php
index 4cc7c69f6530096c3d3a7b3b1ed6b35baa655ec8..c2c7642e2d4b24507eb881a4d80a30a2a1c6c7b7 100644
--- a/core/modules/system/tests/src/Functional/Theme/TwigRegistryLoaderTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/TwigRegistryLoaderTest.php
@@ -19,6 +19,11 @@ class TwigRegistryLoaderTest extends BrowserTestBase {
    */
   public static $modules = ['twig_theme_test', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @var \Drupal\Core\Template\TwigEnvironment
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/TwigSettingsTest.php b/core/modules/system/tests/src/Functional/Theme/TwigSettingsTest.php
index d0c333606c3a50c3d4eecabcda2aeb7147a32b25..2cc8e24d0c5833be75a4b2b535e5f7183fe73255 100644
--- a/core/modules/system/tests/src/Functional/Theme/TwigSettingsTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/TwigSettingsTest.php
@@ -19,6 +19,11 @@ class TwigSettingsTest extends BrowserTestBase {
    */
   public static $modules = ['theme_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensures Twig template auto reload setting can be overridden.
    */
diff --git a/core/modules/system/tests/src/Functional/Theme/TwigTransTest.php b/core/modules/system/tests/src/Functional/Theme/TwigTransTest.php
index 75596f7ade96f8bc9edeeabeddbdc6a82fd8e010..2b2ae0865f1be360901e60fa15b013112e2f65f5 100644
--- a/core/modules/system/tests/src/Functional/Theme/TwigTransTest.php
+++ b/core/modules/system/tests/src/Functional/Theme/TwigTransTest.php
@@ -25,6 +25,11 @@ class TwigTransTest extends BrowserTestBase {
     'language',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An administrative user for testing.
    *
diff --git a/core/modules/system/tests/src/Functional/Update/AdminThemeUpdateTest.php b/core/modules/system/tests/src/Functional/Update/AdminThemeUpdateTest.php
index 8fa4e07a864fa7590405cffbff0176e6ccc62c8b..52bdbb254809019054ae4ef38934e4189c73ac16 100644
--- a/core/modules/system/tests/src/Functional/Update/AdminThemeUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/AdminThemeUpdateTest.php
@@ -12,6 +12,11 @@
  */
 class AdminThemeUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithAutomatedCronTest.php b/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithAutomatedCronTest.php
index e967f1701f285d7d34a8c25d1f35da79b27c1518..3cd9542b01bed72a79f939b55228c4f0b6b122a4 100644
--- a/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithAutomatedCronTest.php
+++ b/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithAutomatedCronTest.php
@@ -12,6 +12,11 @@
  */
 class AutomatedCronUpdateWithAutomatedCronTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithoutAutomatedCronTest.php b/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithoutAutomatedCronTest.php
index c131c7059238299a2fff26337a28b51a9e902d39..41243240bd92109dc5cc2f6614c9f79746470e17 100644
--- a/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithoutAutomatedCronTest.php
+++ b/core/modules/system/tests/src/Functional/Update/AutomatedCronUpdateWithoutAutomatedCronTest.php
@@ -12,6 +12,11 @@
  */
 class AutomatedCronUpdateWithoutAutomatedCronTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/BrokenCacheUpdateTest.php b/core/modules/system/tests/src/Functional/Update/BrokenCacheUpdateTest.php
index 2ad68d2ecf0f8c9f8795863496e192b096346381..300676a2a38f1912cf4ac319a9746986c9f31923 100644
--- a/core/modules/system/tests/src/Functional/Update/BrokenCacheUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/BrokenCacheUpdateTest.php
@@ -13,6 +13,11 @@
  */
 class BrokenCacheUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/ConfigOverridesUpdateTest.php b/core/modules/system/tests/src/Functional/Update/ConfigOverridesUpdateTest.php
index e18195da10e6726b99f3699da15de66e5c4b4080..8d565ac85237e40481278af71e7b2aa56eab064c 100644
--- a/core/modules/system/tests/src/Functional/Update/ConfigOverridesUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/ConfigOverridesUpdateTest.php
@@ -14,6 +14,11 @@
  */
 class ConfigOverridesUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/DependencyHookInvocationTest.php b/core/modules/system/tests/src/Functional/Update/DependencyHookInvocationTest.php
index 203d89ef2a70d29219ce6a73bfcabb826fc38a24..d967fa86f557660bc23119eac25a5bccdb157b69 100644
--- a/core/modules/system/tests/src/Functional/Update/DependencyHookInvocationTest.php
+++ b/core/modules/system/tests/src/Functional/Update/DependencyHookInvocationTest.php
@@ -19,6 +19,11 @@ class DependencyHookInvocationTest extends BrowserTestBase {
    */
   public static $modules = ['update_test_0', 'update_test_1', 'update_test_2'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     require_once $this->root . '/core/includes/update.inc';
diff --git a/core/modules/system/tests/src/Functional/Update/DependencyMissingTest.php b/core/modules/system/tests/src/Functional/Update/DependencyMissingTest.php
index e11999a46c2312d0a3f5c63cdeec367098398f26..b7fced809c2b7f4d55dd8fec59f54533aea0a366 100644
--- a/core/modules/system/tests/src/Functional/Update/DependencyMissingTest.php
+++ b/core/modules/system/tests/src/Functional/Update/DependencyMissingTest.php
@@ -18,6 +18,11 @@ class DependencyMissingTest extends BrowserTestBase {
    */
   public static $modules = ['update_test_0', 'update_test_2'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     // Only install update_test_2.module, even though its updates have a
     // dependency on update_test_3.module.
diff --git a/core/modules/system/tests/src/Functional/Update/DependencyOrderingTest.php b/core/modules/system/tests/src/Functional/Update/DependencyOrderingTest.php
index 0f168aa78f5ca1dc5598e47df74bdee3ef811489..649f9c93b568ddebaebb4c13a3404829d7806b24 100644
--- a/core/modules/system/tests/src/Functional/Update/DependencyOrderingTest.php
+++ b/core/modules/system/tests/src/Functional/Update/DependencyOrderingTest.php
@@ -18,6 +18,11 @@ class DependencyOrderingTest extends BrowserTestBase {
    */
   public static $modules = ['update_test_0', 'update_test_1', 'update_test_2', 'update_test_3'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     require_once $this->root . '/core/includes/update.inc';
diff --git a/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionDefaultTest.php b/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionDefaultTest.php
index fd8f6cf19245be9ab4d8395d5b467094b98156ca..71375b0e3052b5c6359c0e4922de99cfe1266beb 100644
--- a/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionDefaultTest.php
+++ b/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionDefaultTest.php
@@ -18,6 +18,11 @@ class EntityUpdateAddRevisionDefaultTest extends UpdatePathTestBase {
   use EntityDefinitionTestTrait;
   use DbUpdatesTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The state service.
    *
diff --git a/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionTranslationAffectedTest.php b/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionTranslationAffectedTest.php
index 0a3ebbe992ac01e4623e8dacd482a0241df31a38..2c5fccb048b9518d174f310036de6152cbd4d233 100644
--- a/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionTranslationAffectedTest.php
+++ b/core/modules/system/tests/src/Functional/Update/EntityUpdateAddRevisionTranslationAffectedTest.php
@@ -30,6 +30,11 @@ class EntityUpdateAddRevisionTranslationAffectedTest extends UpdatePathTestBase
    */
   protected static $modules = ['entity_test_update'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/EntityUpdateInitialTest.php b/core/modules/system/tests/src/Functional/Update/EntityUpdateInitialTest.php
index 7a85744b26ffa72dab947999f3cc663129fe8fd3..1d9a698b1b44cc9ac32946f8cd1043ea76b9c5d1 100644
--- a/core/modules/system/tests/src/Functional/Update/EntityUpdateInitialTest.php
+++ b/core/modules/system/tests/src/Functional/Update/EntityUpdateInitialTest.php
@@ -14,6 +14,11 @@
  */
 class EntityUpdateInitialTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/EntityUpdateToPublishableTest.php b/core/modules/system/tests/src/Functional/Update/EntityUpdateToPublishableTest.php
index e887fd561cfa7928f28d792307cd2699b0e832f8..fd9a1d95e29fee59e562ab8275653ecebd2ba99d 100644
--- a/core/modules/system/tests/src/Functional/Update/EntityUpdateToPublishableTest.php
+++ b/core/modules/system/tests/src/Functional/Update/EntityUpdateToPublishableTest.php
@@ -17,6 +17,11 @@ class EntityUpdateToPublishableTest extends UpdatePathTestBase {
   use EntityDefinitionTestTrait;
   use DbUpdatesTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The entity type manager service.
    *
diff --git a/core/modules/system/tests/src/Functional/Update/FieldSchemaDataUninstallUpdateTest.php b/core/modules/system/tests/src/Functional/Update/FieldSchemaDataUninstallUpdateTest.php
index 1beb62b73de78233bc57ec949a564930371a13fc..e4c90ebe7b03659f8e1273c502ba53880384beaf 100644
--- a/core/modules/system/tests/src/Functional/Update/FieldSchemaDataUninstallUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/FieldSchemaDataUninstallUpdateTest.php
@@ -14,6 +14,11 @@
  */
 class FieldSchemaDataUninstallUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php b/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php
index ea591fcbd8b053c1bec634255a26960eb96581ae..ebcf7f4c01aa8c19b6d8927290a9bb8e3a5d9772 100644
--- a/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php
@@ -13,6 +13,11 @@
  */
 class FilterHtmlUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/InstallProfileSystemInstall8300Test.php b/core/modules/system/tests/src/Functional/Update/InstallProfileSystemInstall8300Test.php
index 0a1d03ff36852ee31e92c81d3b983232bf7bb569..ced5847bc6d4858d39b061460c31663980860d00 100644
--- a/core/modules/system/tests/src/Functional/Update/InstallProfileSystemInstall8300Test.php
+++ b/core/modules/system/tests/src/Functional/Update/InstallProfileSystemInstall8300Test.php
@@ -13,6 +13,11 @@
  */
 class InstallProfileSystemInstall8300Test extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/InvalidUpdateHookTest.php b/core/modules/system/tests/src/Functional/Update/InvalidUpdateHookTest.php
index 44fdf81ab9091c6407734635aca7a939d06dab76..51fb4d2807b676053348d1be44c358dd2629da86 100644
--- a/core/modules/system/tests/src/Functional/Update/InvalidUpdateHookTest.php
+++ b/core/modules/system/tests/src/Functional/Update/InvalidUpdateHookTest.php
@@ -22,6 +22,11 @@ class InvalidUpdateHookTest extends BrowserTestBase {
    */
   public static $modules = ['update_test_invalid_hook', 'update_script_test', 'dblog'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * URL for the upgrade script.
    *
diff --git a/core/modules/system/tests/src/Functional/Update/LocalActionsAndTasksConvertedIntoBlocksUpdateTest.php b/core/modules/system/tests/src/Functional/Update/LocalActionsAndTasksConvertedIntoBlocksUpdateTest.php
index ff4075e9e6939bf2745c96311840f95c7ff56557..b343d7ac04b5470b3169d6d272f70fa2c1ca12de 100644
--- a/core/modules/system/tests/src/Functional/Update/LocalActionsAndTasksConvertedIntoBlocksUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/LocalActionsAndTasksConvertedIntoBlocksUpdateTest.php
@@ -15,6 +15,11 @@
  */
 class LocalActionsAndTasksConvertedIntoBlocksUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/MenuBlockPostUpdateTest.php b/core/modules/system/tests/src/Functional/Update/MenuBlockPostUpdateTest.php
index 77ce66dcf4e0c31c8aad8a40f614885742617a65..0e4d6c63b3cb19359d593d16ace94392a899ffed 100644
--- a/core/modules/system/tests/src/Functional/Update/MenuBlockPostUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/MenuBlockPostUpdateTest.php
@@ -13,6 +13,11 @@
  */
 class MenuBlockPostUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleFilledTest.php b/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleFilledTest.php
index 58429e3cbc3a1bc420459da592fcae1f8fbd5af6..6433bf4a66531b50ad6a0d7935c6250ca2dcb4af 100644
--- a/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleFilledTest.php
+++ b/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleFilledTest.php
@@ -10,6 +10,11 @@
  */
 class MenuTreeSerializationTitleFilledTest extends MenuTreeSerializationTitleTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleTest.php b/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleTest.php
index 1a3fa84f4209a3fbfbce27368465c7756af60c18..d9572b06e2655649a843553178101eb6a325a6dd 100644
--- a/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleTest.php
+++ b/core/modules/system/tests/src/Functional/Update/MenuTreeSerializationTitleTest.php
@@ -13,6 +13,11 @@
  */
 class MenuTreeSerializationTitleTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/MoveActionsToCoreTest.php b/core/modules/system/tests/src/Functional/Update/MoveActionsToCoreTest.php
index e5c21f23b592dcef83119057e0079a82d844ba15..ad0e8259305c0eb78cec2ac8a4bffe6523ee8d17 100644
--- a/core/modules/system/tests/src/Functional/Update/MoveActionsToCoreTest.php
+++ b/core/modules/system/tests/src/Functional/Update/MoveActionsToCoreTest.php
@@ -13,6 +13,11 @@
  */
 class MoveActionsToCoreTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/NoDependenciesUpdateTest.php b/core/modules/system/tests/src/Functional/Update/NoDependenciesUpdateTest.php
index 152d66780039ae9114998051ffec300eb956251f..23c88142b56cda77f22c2eeff5c6cbf594c56631 100644
--- a/core/modules/system/tests/src/Functional/Update/NoDependenciesUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/NoDependenciesUpdateTest.php
@@ -12,6 +12,11 @@
  */
 class NoDependenciesUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/PageTitleConvertedIntoBlockUpdateTest.php b/core/modules/system/tests/src/Functional/Update/PageTitleConvertedIntoBlockUpdateTest.php
index 6e17506220d06d99177ce9d52f515abfa2b7589e..6548db66f8dbff39cfbdb313ddf1ca82ffe4503f 100644
--- a/core/modules/system/tests/src/Functional/Update/PageTitleConvertedIntoBlockUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/PageTitleConvertedIntoBlockUpdateTest.php
@@ -15,6 +15,11 @@
  */
 class PageTitleConvertedIntoBlockUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/PathAliasToEntityUpdateTest.php b/core/modules/system/tests/src/Functional/Update/PathAliasToEntityUpdateTest.php
index 0d0a1401b9e74abbf2848d83149a6c83c0b1a923..7a860906e93848b5b6580a1e84fbbf57d3a22eb3 100644
--- a/core/modules/system/tests/src/Functional/Update/PathAliasToEntityUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/PathAliasToEntityUpdateTest.php
@@ -13,6 +13,11 @@
  */
 class PathAliasToEntityUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/RebuildScriptTest.php b/core/modules/system/tests/src/Functional/Update/RebuildScriptTest.php
index a684b037f71db88155a9f6fd965335e67e9ddc07..d47e9771a4a5769923cf41f4bef1b1369b25ee84 100644
--- a/core/modules/system/tests/src/Functional/Update/RebuildScriptTest.php
+++ b/core/modules/system/tests/src/Functional/Update/RebuildScriptTest.php
@@ -12,6 +12,11 @@
  */
 class RebuildScriptTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test redirect in rebuild.php.
    */
diff --git a/core/modules/system/tests/src/Functional/Update/RecalculatedDependencyTest.php b/core/modules/system/tests/src/Functional/Update/RecalculatedDependencyTest.php
index 2cda26e9a14044087108fa7ce4bb2b0d624fe6fd..e2f262a8ebdc468799c23be2465f0b9ab1c5568f 100644
--- a/core/modules/system/tests/src/Functional/Update/RecalculatedDependencyTest.php
+++ b/core/modules/system/tests/src/Functional/Update/RecalculatedDependencyTest.php
@@ -12,6 +12,11 @@
  */
 class RecalculatedDependencyTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/RemoveResponseGzipFromSystemPerformanceConfigurationTest.php b/core/modules/system/tests/src/Functional/Update/RemoveResponseGzipFromSystemPerformanceConfigurationTest.php
index f7f772b13e7c616a8d50d6caa0d00b3690b0e181..9ab66fd26969d4167fb823f817e64d437e748956 100644
--- a/core/modules/system/tests/src/Functional/Update/RemoveResponseGzipFromSystemPerformanceConfigurationTest.php
+++ b/core/modules/system/tests/src/Functional/Update/RemoveResponseGzipFromSystemPerformanceConfigurationTest.php
@@ -12,6 +12,11 @@
  */
 class RemoveResponseGzipFromSystemPerformanceConfigurationTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationFilledTest.php b/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationFilledTest.php
index 93c9c8e23494d4f9d18817ccd61e9f2f1f5050ad..e7454c03104589c56667eb3af33716a41002b2b9 100644
--- a/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationFilledTest.php
+++ b/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationFilledTest.php
@@ -10,6 +10,11 @@
  */
 class RouterIndexOptimizationFilledTest extends RouterIndexOptimizationTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationTest.php b/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationTest.php
index f4672b4cd117856c92fcf791eaf32e5125853697..884a8dc265b47efaff03740ffbfdc14ff6fc2bf6 100644
--- a/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationTest.php
+++ b/core/modules/system/tests/src/Functional/Update/RouterIndexOptimizationTest.php
@@ -12,6 +12,11 @@
  */
 class RouterIndexOptimizationTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/SevenSecondaryLocalTasksConvertedIntoBlockUpdateTest.php b/core/modules/system/tests/src/Functional/Update/SevenSecondaryLocalTasksConvertedIntoBlockUpdateTest.php
index b0a58623a5461a1baa2c0c48205a2027807a7874..f0427d31a2f8e65e03e95b7c36ee528d0bff4e5c 100644
--- a/core/modules/system/tests/src/Functional/Update/SevenSecondaryLocalTasksConvertedIntoBlockUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/SevenSecondaryLocalTasksConvertedIntoBlockUpdateTest.php
@@ -14,6 +14,11 @@
  */
 class SevenSecondaryLocalTasksConvertedIntoBlockUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/SiteBrandingConvertedIntoBlockUpdateTest.php b/core/modules/system/tests/src/Functional/Update/SiteBrandingConvertedIntoBlockUpdateTest.php
index 56b988e956d218de2ca207c1e428248c3b03ba4a..4470398b25a31bd3c56b029239238188cd356d5b 100644
--- a/core/modules/system/tests/src/Functional/Update/SiteBrandingConvertedIntoBlockUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/SiteBrandingConvertedIntoBlockUpdateTest.php
@@ -12,6 +12,11 @@
  */
 class SiteBrandingConvertedIntoBlockUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/StableBaseThemeUpdateTest.php b/core/modules/system/tests/src/Functional/Update/StableBaseThemeUpdateTest.php
index e00a3a94a220d6a764a9637f55a63c1b679144de..5675cb99bb30306897d4c6794493d46fa3a21733 100644
--- a/core/modules/system/tests/src/Functional/Update/StableBaseThemeUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/StableBaseThemeUpdateTest.php
@@ -33,6 +33,11 @@ class StableBaseThemeUpdateTest extends UpdatePathTestBase implements ServicePro
    */
   protected $themeHandler;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdateActionsWithEntityPluginsTest.php b/core/modules/system/tests/src/Functional/Update/UpdateActionsWithEntityPluginsTest.php
index 764c92c5ffb54100fa831e0508b6da1dcc3a6377..db5928ef1a9ac032db03c1a7b7f86176e289c239 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdateActionsWithEntityPluginsTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdateActionsWithEntityPluginsTest.php
@@ -13,6 +13,11 @@
  */
 class UpdateActionsWithEntityPluginsTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdateCacheTest.php b/core/modules/system/tests/src/Functional/Update/UpdateCacheTest.php
index 1d9765da4ddf17dca44dab0e2be4e50bb7d66262..0dc56602c3e9e0c55c010ee16ace77aa201e1b6b 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdateCacheTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdateCacheTest.php
@@ -14,6 +14,11 @@
 class UpdateCacheTest extends BrowserTestBase {
   use RequirementsPageTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that caches are cleared during updates.
    *
diff --git a/core/modules/system/tests/src/Functional/Update/UpdateEntityDisplayTest.php b/core/modules/system/tests/src/Functional/Update/UpdateEntityDisplayTest.php
index 187c7ac9199b43b5449cec8699bd909d5c717ce9..5599462ebdc0c6ca67f564cdcc8a6b977a404c92 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdateEntityDisplayTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdateEntityDisplayTest.php
@@ -14,6 +14,11 @@
  */
 class UpdateEntityDisplayTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePathNewDependencyTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePathNewDependencyTest.php
index 57a53278c4349bf6c31b906b809de6e2b1ebc363..8f10ef76ce711e993c414e3cc4f8a419f4374ed2 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePathNewDependencyTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePathNewDependencyTest.php
@@ -13,6 +13,11 @@
  */
 class UpdatePathNewDependencyTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseFilledTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseFilledTest.php
index 45c3d847758e5a71640fef2d787db3df46625caa..c0fcdf4f58149023046b0ead7149e745b2fdf81c 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseFilledTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseFilledTest.php
@@ -14,6 +14,11 @@
  */
 class UpdatePathRC1TestBaseFilledTest extends UpdatePathRC1TestBaseTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseTest.php
index af2552492aa4913d8b9beb5174b4942af434e626..c3e0cdb05154f9240ff20ec8c029b475954b2e7b 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePathRC1TestBaseTest.php
@@ -18,6 +18,11 @@ class UpdatePathRC1TestBaseTest extends UpdatePathTestBase {
    */
   protected static $modules = ['update_test_schema'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePathTestBaseFilledTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePathTestBaseFilledTest.php
index 5cc23b007d6593208d370be3b7ee18c0e621c1ff..e03073f00bde337e42b6a88568364c85c17038ea 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePathTestBaseFilledTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePathTestBaseFilledTest.php
@@ -16,6 +16,11 @@
  */
 class UpdatePathTestBaseFilledTest extends UpdatePathTestBaseTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePathTestJavaScriptTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePathTestJavaScriptTest.php
index d5bcb16823c98378c26b1ea800998a45f6cf9c2f..473c392aa03e03bc491fb02daf6807212963ead3 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePathTestJavaScriptTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePathTestJavaScriptTest.php
@@ -12,6 +12,11 @@
  */
 class UpdatePathTestJavaScriptTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingFilledTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingFilledTest.php
index 4eaec54e366ec985a2312282ff86e3c894832086..6be4f333cb4a6fcd57ff662cf90ab452b7de34cd 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingFilledTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingFilledTest.php
@@ -10,6 +10,11 @@
  */
 class UpdatePathWithBrokenRoutingFilledTest extends UpdatePathWithBrokenRoutingTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingTest.php
index c54804712cfa74c082c2dd4ab72dbb72f4ee863b..17a70c0215b37ff500c333866ae1f27e23004f2d 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePathWithBrokenRoutingTest.php
@@ -12,6 +12,11 @@
  */
 class UpdatePathWithBrokenRoutingTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateFailingTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateFailingTest.php
index a01476534c0a2f2810a6653ce9785b1a59798dbd..5c6b223d6fbb51c68f500bce87afbbda8dca9f3b 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateFailingTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateFailingTest.php
@@ -12,6 +12,11 @@
  */
 class UpdatePostUpdateFailingTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateTest.php b/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateTest.php
index 3e2c46a99c1a4a593b17a3661f3ce494828ca7b6..1015e7a138ebb4304487737a38816f8adb6d1774 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatePostUpdateTest.php
@@ -13,6 +13,11 @@
  */
 class UpdatePostUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdateSchemaTest.php b/core/modules/system/tests/src/Functional/Update/UpdateSchemaTest.php
index aa28be020d75f1caf9228a1ded4eb7a7b870a3c5..193704b2f6dcb727e196f5886129eff9e3381e6e 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdateSchemaTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdateSchemaTest.php
@@ -21,6 +21,11 @@ class UpdateSchemaTest extends BrowserTestBase {
    */
   public static $modules = ['update_test_schema'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @var \Drupal\user\UserInterface
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdateScriptTest.php b/core/modules/system/tests/src/Functional/Update/UpdateScriptTest.php
index 162cbf482cb1abd768ce91941d10963c884348fd..189a1494573d0a700a7457d04fba8a8728451518 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdateScriptTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdateScriptTest.php
@@ -23,6 +23,11 @@ class UpdateScriptTest extends BrowserTestBase {
    */
   public static $modules = ['update_script_test', 'dblog', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/Functional/Update/UpdatesWith7xTest.php b/core/modules/system/tests/src/Functional/Update/UpdatesWith7xTest.php
index e4c5635928cf026399604f183180104f350dd668..6b08e685ea3cc4108924a09e18f9f32ce405316c 100644
--- a/core/modules/system/tests/src/Functional/Update/UpdatesWith7xTest.php
+++ b/core/modules/system/tests/src/Functional/Update/UpdatesWith7xTest.php
@@ -22,6 +22,11 @@ class UpdatesWith7xTest extends BrowserTestBase {
    */
   public static $modules = ['update_test_with_7x'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The URL for the update page.
    *
diff --git a/core/modules/system/tests/src/FunctionalJavascript/Form/ElementsTableSelectTest.php b/core/modules/system/tests/src/FunctionalJavascript/Form/ElementsTableSelectTest.php
index b565bfd74381ac2fd7c89e8401e527bbdd7a96ae..560ee6c8bf8ac2ae1903f835040a80789694e8bc 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/Form/ElementsTableSelectTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/Form/ElementsTableSelectTest.php
@@ -16,6 +16,11 @@ class ElementsTableSelectTest extends WebDriverTestBase {
    */
   protected static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test the presence of ajax functionality for all options.
    */
diff --git a/core/modules/system/tests/src/FunctionalJavascript/Form/RebuildTest.php b/core/modules/system/tests/src/FunctionalJavascript/Form/RebuildTest.php
index 5bbaa8b909b162c7cd16f6e7547b10b8c351b527..9b38a1625812cd00fc54fef6a8e5e6062a51a70d 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/Form/RebuildTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/Form/RebuildTest.php
@@ -21,6 +21,11 @@ class RebuildTest extends WebDriverTestBase {
    */
   protected static $modules = ['node', 'form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user for testing.
    *
diff --git a/core/modules/system/tests/src/FunctionalJavascript/Form/TriggeringElementTest.php b/core/modules/system/tests/src/FunctionalJavascript/Form/TriggeringElementTest.php
index 41733ec46e3db89d9624a06bc1a3fe48880e76c2..3a3840d2d2297cbadf58a2789b6d02170a2c4fd9 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/Form/TriggeringElementTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/Form/TriggeringElementTest.php
@@ -16,6 +16,11 @@ class TriggeringElementTest extends WebDriverTestBase {
    */
   protected static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the the triggering element when no button information is included.
    *
diff --git a/core/modules/system/tests/src/FunctionalJavascript/FrameworkTest.php b/core/modules/system/tests/src/FunctionalJavascript/FrameworkTest.php
index c23f9847c05b961d46c929f98346bc72aaa2c943..f2ff799f881229540d6ce9c685f6dc523a662d94 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/FrameworkTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/FrameworkTest.php
@@ -17,6 +17,11 @@ class FrameworkTest extends WebDriverTestBase {
    */
   protected static $modules = ['node', 'ajax_test', 'ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests that new JavaScript and CSS files are lazy-loaded on an AJAX request.
    */
diff --git a/core/modules/system/tests/src/FunctionalJavascript/ModalRendererTest.php b/core/modules/system/tests/src/FunctionalJavascript/ModalRendererTest.php
index 3597ba46dd2e07ae9429693e1642b78d43141d9a..e7ce0429effe4dcfce4c41387ef6f1e6009f194b 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/ModalRendererTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/ModalRendererTest.php
@@ -16,6 +16,11 @@ class ModalRendererTest extends WebDriverTestBase {
    */
   public static $modules = ['system', 'dialog_renderer_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that links respect 'data-dialog-renderer' attribute.
    */
diff --git a/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTest.php b/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTest.php
index 4eac4ec6c7eaeafa1088cc9dc7d17f6bcd0136e9..f2d44592c60267ce3eff0ed9e3ec000264277c2e 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/OffCanvasTest.php
@@ -25,6 +25,11 @@ class OffCanvasTest extends OffCanvasTestBase {
     'off_canvas_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that non-contextual links will work with the off-canvas dialog.
    *
diff --git a/core/modules/system/tests/src/FunctionalJavascript/System/DateFormatTest.php b/core/modules/system/tests/src/FunctionalJavascript/System/DateFormatTest.php
index 4a0c02b01e89e5d3c1e944aef702e07a66eca355..3460f15b3b815eddf68744797a779cb15084254e 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/System/DateFormatTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/System/DateFormatTest.php
@@ -17,6 +17,11 @@ class DateFormatTest extends WebDriverTestBase {
    */
   protected static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/system/tests/src/FunctionalJavascript/ThemeSettingsFormTest.php b/core/modules/system/tests/src/FunctionalJavascript/ThemeSettingsFormTest.php
index 00bb56264028c265ae8d357c30da489d7be42e3e..f80ae96facec1549b6a66a9bbbf99e9c354906a2 100644
--- a/core/modules/system/tests/src/FunctionalJavascript/ThemeSettingsFormTest.php
+++ b/core/modules/system/tests/src/FunctionalJavascript/ThemeSettingsFormTest.php
@@ -20,6 +20,11 @@ class ThemeSettingsFormTest extends WebDriverTestBase {
    */
   public static $modules = ['file'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/EarlyDateTest.php b/core/modules/taxonomy/tests/src/Functional/EarlyDateTest.php
index f0b31aa171c5f7146bceb71cca74cc14a9587694..74b0093738bdd9743b52863a93df2a7d03337a7f 100644
--- a/core/modules/taxonomy/tests/src/Functional/EarlyDateTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/EarlyDateTest.php
@@ -20,6 +20,11 @@ class EarlyDateTest extends TaxonomyTestBase {
    */
   public static $modules = ['node', 'datetime'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonAnonTest.php b/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonAnonTest.php
index ee3effc572a23fbb21e26f28c13cafa522eb5807..7a3a57a8cab7d9a5ada0509d034132d91d6a48c0 100644
--- a/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonAnonTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonAnonTest.php
@@ -20,6 +20,11 @@ class TermHalJsonAnonTest extends TermResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonBasicAuthTest.php b/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonBasicAuthTest.php
index 576615607239298c6332ab0d99c85d64a3456d89..43adecebc2b668728a34eae6f5b4304f65b5c3ce 100644
--- a/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonBasicAuthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class TermHalJsonBasicAuthTest extends TermHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonCookieTest.php b/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonCookieTest.php
index f949e7a8340a60c42d9ce57c36991c4b01f69971..face86285a48844f466fad5b22323cdd2d94861d 100644
--- a/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonCookieTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Hal/TermHalJsonCookieTest.php
@@ -15,4 +15,9 @@ class TermHalJsonCookieTest extends TermHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonAnonTest.php b/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonAnonTest.php
index e2c1bc86bd90549a80a446756fb856dbef6285c2..1775ddd2f001cf2073a123c091d4e7884395f07a 100644
--- a/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonAnonTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class VocabularyHalJsonAnonTest extends VocabularyResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonBasicAuthTest.php b/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonBasicAuthTest.php
index d8c17e6d3a0f234a07efa2f28894af783f3a1dcf..ad9d2340369813e326a8949a1bb0aca370e08532 100644
--- a/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonBasicAuthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class VocabularyHalJsonBasicAuthTest extends VocabularyResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonCookieTest.php b/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonCookieTest.php
index 13a44dbb93e5960dd4bac2f519da1803f4feffca..3e8b3cc7d413d7f4f08b73117a4ba8b7758bade1 100644
--- a/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonCookieTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Hal/VocabularyHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class VocabularyHalJsonCookieTest extends VocabularyResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/LoadMultipleTest.php b/core/modules/taxonomy/tests/src/Functional/LoadMultipleTest.php
index 14ce5548c678187031139b8862a9363c504707fe..5a05fe6363bfbe312301e44569c370dd4b37122e 100644
--- a/core/modules/taxonomy/tests/src/Functional/LoadMultipleTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/LoadMultipleTest.php
@@ -12,6 +12,11 @@
  */
 class LoadMultipleTest extends TaxonomyTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->drupalLogin($this->drupalCreateUser(['administer taxonomy']));
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonAnonTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonAnonTest.php
index 7d87337597c137f653fb254792af4491565d85ed..19aef9697a8119a4376a0af83e313d44e23af7d5 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonAnonTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonAnonTest.php
@@ -21,4 +21,9 @@ class TermJsonAnonTest extends TermResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonBasicAuthTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonBasicAuthTest.php
index 959e2bb187a9e99eecd6d82b7d75e1e4e9d878d8..8bb4c921cf2c930e15b2659edac472f8638fc8e5 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonBasicAuthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class TermJsonBasicAuthTest extends TermResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonCookieTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonCookieTest.php
index 88dd70c606408cf2a678b550a9187437052a6263..6a721186a81e83442f485b6543035102d1869255 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonCookieTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/TermJsonCookieTest.php
@@ -26,4 +26,9 @@ class TermJsonCookieTest extends TermResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlAnonTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlAnonTest.php
index 69abeaf210a818bb01566c26a54dabc7a30b6ddd..ff05095d3d60075466f5602ebd32503c5164bf5f 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlAnonTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlAnonTest.php
@@ -23,6 +23,11 @@ class TermXmlAnonTest extends TermResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlBasicAuthTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlBasicAuthTest.php
index 8eacb85c1c08499a88f5dfc5973c17bcb6922503..f907dddb0b34ff1c7ae02fc5ec891f11ec15c5b4 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlBasicAuthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class TermXmlBasicAuthTest extends TermResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlCookieTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlCookieTest.php
index 3de95fdabab3b761ae3365a7352c2924a1c11247..a83fe821fdc0f9f13f9962073d051671d98c80ca 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlCookieTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/TermXmlCookieTest.php
@@ -18,6 +18,11 @@ class TermXmlCookieTest extends TermResourceTestBase {
    */
   protected static $format = 'xml';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonAnonTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonAnonTest.php
index a85da938272ec06567a96231079b15f5f9e7bd30..956a3079e4fa574c7ad9ba529153eb396aa90b1e 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonAnonTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonAnonTest.php
@@ -21,6 +21,11 @@ class VocabularyJsonAnonTest extends VocabularyResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Disable the GET test coverage due to bug in taxonomy module.
    * @todo Fix in https://www.drupal.org/node/2805281: remove this override.
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonBasicAuthTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonBasicAuthTest.php
index ec0d67e2b2ed650f0184f18d3c545685718db203..4bcb94e93b7616f6f3952b94b312e0db8a28f792 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonBasicAuthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class VocabularyJsonBasicAuthTest extends VocabularyResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonCookieTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonCookieTest.php
index 51c79a6a8c45f72bf9b2de9605b6045184cf307d..63c2f37719686dfd7fc8eeb0adefb87cb38387ff 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonCookieTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyJsonCookieTest.php
@@ -26,4 +26,9 @@ class VocabularyJsonCookieTest extends VocabularyResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlAnonTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlAnonTest.php
index ac8da3d741eff88e03ad17273ab2348bfd55a420..64ab45b93606b96420ef215ef15b5f9ed460ee40 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlAnonTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlAnonTest.php
@@ -23,4 +23,9 @@ class VocabularyXmlAnonTest extends VocabularyResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlBasicAuthTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlBasicAuthTest.php
index 52b3741a9aff8c1bea0e85ad01fdb22dbcf0630c..b0a459098267f0b699fc650f8478a12dfc56084a 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlBasicAuthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class VocabularyXmlBasicAuthTest extends VocabularyResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlCookieTest.php b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlCookieTest.php
index 51e7e20e49dd6c504d137c6949b99827aba219b5..1b87db1b906fc7abb6b2b93a3fe595aca9488554 100644
--- a/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlCookieTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Rest/VocabularyXmlCookieTest.php
@@ -28,4 +28,9 @@ class VocabularyXmlCookieTest extends VocabularyResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/taxonomy/tests/src/Functional/RssTest.php b/core/modules/taxonomy/tests/src/Functional/RssTest.php
index 00e380e048edf57c827d7aecbfdc42d8c2f1d612..b0488f1d0f0ad357eabaaa0a7d003a2cfa4e4686 100644
--- a/core/modules/taxonomy/tests/src/Functional/RssTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/RssTest.php
@@ -20,6 +20,11 @@ class RssTest extends TaxonomyTestBase {
    */
   public static $modules = ['node', 'field_ui', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Vocabulary for testing.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/TaxonomyImageTest.php b/core/modules/taxonomy/tests/src/Functional/TaxonomyImageTest.php
index a22cbe179ca876c7903ef24da8952d59454da8ef..6bd4ef5bca5d6a72bbe0dfc2847de37cdd617bc8 100644
--- a/core/modules/taxonomy/tests/src/Functional/TaxonomyImageTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TaxonomyImageTest.php
@@ -34,6 +34,11 @@ class TaxonomyImageTest extends TaxonomyTestBase {
    */
   public static $modules = ['image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/taxonomy/tests/src/Functional/TaxonomyTermIndentationTest.php b/core/modules/taxonomy/tests/src/Functional/TaxonomyTermIndentationTest.php
index 89de4c54989f3c89604f84c4892afd1d51c6f013..8e580023e79e324a87a066a1e2576fa454b4fad5 100644
--- a/core/modules/taxonomy/tests/src/Functional/TaxonomyTermIndentationTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TaxonomyTermIndentationTest.php
@@ -16,6 +16,11 @@ class TaxonomyTermIndentationTest extends TaxonomyTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Vocabulary for testing.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/TaxonomyTermPagerTest.php b/core/modules/taxonomy/tests/src/Functional/TaxonomyTermPagerTest.php
index 6244c68b55df22a848cf38ecc1030a4b840387c5..99c80db177bac3cf9e45002437ee2ec581462445 100644
--- a/core/modules/taxonomy/tests/src/Functional/TaxonomyTermPagerTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TaxonomyTermPagerTest.php
@@ -16,6 +16,11 @@ class TaxonomyTermPagerTest extends TaxonomyTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Vocabulary for testing.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/TermAccessTest.php b/core/modules/taxonomy/tests/src/Functional/TermAccessTest.php
index 4836fcd6555caf7faae40391d4dd4e8f11cf684c..a69fdf144d41598a8022f748882838f1e157d714 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermAccessTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermAccessTest.php
@@ -15,6 +15,11 @@ class TermAccessTest extends TaxonomyTestBase {
 
   use AssertPageCacheContextsAndTagsTrait;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test access control functionality for taxonomy terms.
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/TermAutocompleteTest.php b/core/modules/taxonomy/tests/src/Functional/TermAutocompleteTest.php
index 6304976176a7cf935a6d8395115c753104688523..d3b3845d8a6c9d912c34bdf2cfc8bb7c68ec0d86 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermAutocompleteTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermAutocompleteTest.php
@@ -23,6 +23,11 @@ class TermAutocompleteTest extends TaxonomyTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The vocabulary.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/TermCacheTagsTest.php b/core/modules/taxonomy/tests/src/Functional/TermCacheTagsTest.php
index 378d02c755f0790aa0aeaac52b255a3c00719162..52fef002993f9392e76ec6d97021217927c5b7b7 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermCacheTagsTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermCacheTagsTest.php
@@ -18,6 +18,11 @@ class TermCacheTagsTest extends EntityWithUriCacheTagsTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/TermContextualLinksTest.php b/core/modules/taxonomy/tests/src/Functional/TermContextualLinksTest.php
index 997e698b9eff62a431c3edbaf6e2eed1627f763e..e24ca634f465fa691ed29cb8786cdb427ad6ecc6 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermContextualLinksTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermContextualLinksTest.php
@@ -16,6 +16,11 @@ class TermContextualLinksTest extends TaxonomyTestBase {
     'contextual',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests contextual links.
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/TermIndexTest.php b/core/modules/taxonomy/tests/src/Functional/TermIndexTest.php
index 78618823262ad211cc4404997b8ca8dcc45aae80..dd240bee6dbcee2d25cc10a41250b02702b580e6 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermIndexTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermIndexTest.php
@@ -20,6 +20,11 @@ class TermIndexTest extends TaxonomyTestBase {
    */
   public static $modules = ['views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Vocabulary for testing.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/TermLanguageTest.php b/core/modules/taxonomy/tests/src/Functional/TermLanguageTest.php
index f60e77e534a644d5ae1975d73b648511aec225e7..bc6230c2894dc5ef53deb61fdc9ec19a5f9480ac 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermLanguageTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermLanguageTest.php
@@ -14,6 +14,11 @@ class TermLanguageTest extends TaxonomyTestBase {
 
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Vocabulary for testing.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/TermTest.php b/core/modules/taxonomy/tests/src/Functional/TermTest.php
index d0f5b306778d768362296e82e4d23a267f81c090..a15a44da66b1522f98aa24c2af81686c013568b8 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermTest.php
@@ -36,6 +36,11 @@ class TermTest extends TaxonomyTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/TermTranslationFieldViewTest.php b/core/modules/taxonomy/tests/src/Functional/TermTranslationFieldViewTest.php
index 236ac70553353903ce0cad4b45ad0533533ac8ba..1153b8ec441f4e366b483fdd4a0041c8e541c5c8 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermTranslationFieldViewTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermTranslationFieldViewTest.php
@@ -41,6 +41,11 @@ class TermTranslationFieldViewTest extends TaxonomyTestBase {
    */
   public static $modules = ['language', 'content_translation', 'taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->setupLanguages();
diff --git a/core/modules/taxonomy/tests/src/Functional/TermTranslationTest.php b/core/modules/taxonomy/tests/src/Functional/TermTranslationTest.php
index 227a589cc87e90232cec8cd340fa9f279bdfbe66..a9ae460f81bb9aa8fd24527dad7b946c58d46cd3 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermTranslationTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermTranslationTest.php
@@ -38,6 +38,11 @@ class TermTranslationTest extends TaxonomyTestBase {
    */
   public static $modules = ['taxonomy', 'language', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/TermTranslationUITest.php b/core/modules/taxonomy/tests/src/Functional/TermTranslationUITest.php
index a71215eda8f4b62aa63cf682ebff62b0499ed09f..74b7b2467c34f12c08410057970f9426b804ae54 100644
--- a/core/modules/taxonomy/tests/src/Functional/TermTranslationUITest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TermTranslationUITest.php
@@ -28,6 +28,11 @@ class TermTranslationUITest extends ContentTranslationUITestBase {
    */
   public static $modules = ['language', 'content_translation', 'taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     $this->entityTypeId = 'taxonomy_term';
     $this->bundle = 'tags';
diff --git a/core/modules/taxonomy/tests/src/Functional/ThemeTest.php b/core/modules/taxonomy/tests/src/Functional/ThemeTest.php
index bf6c6b57daf35f9cafce69e5663bbad344c86d88..e0a8774fc92df0338f0e1312ae1feca3ca71dc30 100644
--- a/core/modules/taxonomy/tests/src/Functional/ThemeTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/ThemeTest.php
@@ -9,6 +9,11 @@
  */
 class ThemeTest extends TaxonomyTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/taxonomy/tests/src/Functional/TokenReplaceTest.php b/core/modules/taxonomy/tests/src/Functional/TokenReplaceTest.php
index 5bd236b642870183febd34245de45a6948a275a5..e8c5b322bfd2efd39c4314d606ff8593b67716d9 100644
--- a/core/modules/taxonomy/tests/src/Functional/TokenReplaceTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/TokenReplaceTest.php
@@ -28,6 +28,11 @@ class TokenReplaceTest extends TaxonomyTestBase {
    */
   protected $fieldName;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->drupalLogin($this->drupalCreateUser(['administer taxonomy', 'bypass node access']));
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/RelationshipNodeTermDataTest.php b/core/modules/taxonomy/tests/src/Functional/Views/RelationshipNodeTermDataTest.php
index 3469870fa43f8f4914857295685d3146188a0535..c78a511b3c76e44a908296107ee69d90e6768385 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/RelationshipNodeTermDataTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/RelationshipNodeTermDataTest.php
@@ -18,6 +18,11 @@ class RelationshipNodeTermDataTest extends TaxonomyTestBase {
    */
   public static $testViews = ['test_taxonomy_node_term_data'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testViewsHandlerRelationshipNodeTermData() {
     $view = Views::getView('test_taxonomy_node_term_data');
     // Tests \Drupal\taxonomy\Plugin\views\relationship\NodeTermData::calculateDependencies().
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/RelationshipRepresentativeNodeTest.php b/core/modules/taxonomy/tests/src/Functional/Views/RelationshipRepresentativeNodeTest.php
index d1de82efedabb4b4abf8c1368ee510c8f2d2189f..f4338152458643078d999e7906984c4f2603d825 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/RelationshipRepresentativeNodeTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/RelationshipRepresentativeNodeTest.php
@@ -18,6 +18,11 @@ class RelationshipRepresentativeNodeTest extends TaxonomyTestBase {
    */
   public static $testViews = ['test_groupwise_term'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the relationship.
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyDefaultArgumentTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyDefaultArgumentTest.php
index d2eb21625d3616909f35fe7f36e2887e9c8d8b8c..e5bb15bffceac581d0b6e4cc99fc67e3633573de 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyDefaultArgumentTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyDefaultArgumentTest.php
@@ -16,6 +16,11 @@ class TaxonomyDefaultArgumentTest extends TaxonomyTestBase {
    */
   public static $testViews = ['taxonomy_default_argument_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests escaping of page title when the taxonomy plugin provides it.
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldAllTermsTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldAllTermsTest.php
index de313e087f10a0a5f06aa15f900922a4698145dc..67bf8e5f34a013b2085de5cf9ea9c571b21e61e6 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldAllTermsTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldAllTermsTest.php
@@ -19,6 +19,11 @@ class TaxonomyFieldAllTermsTest extends TaxonomyTestBase {
    */
   public static $testViews = ['taxonomy_all_terms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the "all terms" field handler.
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldFilterTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldFilterTest.php
index 1b8bbcaa517e9af1dbb38d4db2f97ea9a73bf32a..5df90a6893f3678350515ea29006c9e7552e39c9 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldFilterTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyFieldFilterTest.php
@@ -24,6 +24,11 @@ class TaxonomyFieldFilterTest extends ViewTestBase {
    */
   public static $modules = ['language', 'taxonomy', 'taxonomy_test_views', 'text', 'views', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyIndexTidUiTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyIndexTidUiTest.php
index a269c8fe0df8ffe81174cb5b244b8cc2a38456f9..b2325fdf82d20c4a7b81d704ea611a2f27f04f61 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyIndexTidUiTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyIndexTidUiTest.php
@@ -26,6 +26,11 @@ class TaxonomyIndexTidUiTest extends UITestBase {
    */
   public static $testViews = ['test_filter_taxonomy_index_tid', 'test_taxonomy_term_name'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Modules to enable.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyParentUITest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyParentUITest.php
index d8ab8ea121165cd4a3b72a0123d2aa5d57ce0044..44f9eb5cf6ee30c05d8b8b3fac10fa424a27554e 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyParentUITest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyParentUITest.php
@@ -20,6 +20,11 @@ class TaxonomyParentUITest extends UITestBase {
    */
   public static $testViews = ['test_taxonomy_parent'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyRelationshipTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyRelationshipTest.php
index 3299964909525c40faa5f0358807fd94a2f7d8f7..20f467417e94fdf38435ee1e3b80f21fd9c78651 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyRelationshipTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyRelationshipTest.php
@@ -27,6 +27,11 @@ class TaxonomyRelationshipTest extends TaxonomyTestBase {
    */
   public static $testViews = ['test_taxonomy_term_relationship'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermArgumentDepthTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermArgumentDepthTest.php
index 3505784a078599c9455b31dbb5e06280ed982ff9..0107dea661b23123d8a0a6b19d76b417b1893190 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermArgumentDepthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermArgumentDepthTest.php
@@ -14,6 +14,11 @@ class TaxonomyTermArgumentDepthTest extends TaxonomyTestBase {
    */
   public static $modules = ['taxonomy', 'taxonomy_test_views', 'views', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermFilterDepthTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermFilterDepthTest.php
index 4d7a4fdf03c69cab15c92409f959c88f4cd1cb2f..5cc1ad93dbf50a30ea9241577833c2e5b89c2b35 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermFilterDepthTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermFilterDepthTest.php
@@ -16,6 +16,11 @@ class TaxonomyTermFilterDepthTest extends TaxonomyTestBase {
    */
   public static $modules = ['taxonomy', 'taxonomy_test_views', 'views', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermViewTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermViewTest.php
index 42bfc4989c90843ad5dbc5274bc32aa78d9f179f..13cd7286b11a6910dba9cdb8aba90350ee063270 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermViewTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermViewTest.php
@@ -23,6 +23,11 @@ class TaxonomyTermViewTest extends TaxonomyTestBase {
    */
   public static $modules = ['taxonomy', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An user with permissions to administer taxonomy.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyVocabularyArgumentTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyVocabularyArgumentTest.php
index 8b1d58cf29e6c706478b85586c88f257fb40a98f..1ee93b6805b3e5b927392bc237df1c973a4cb377 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyVocabularyArgumentTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TaxonomyVocabularyArgumentTest.php
@@ -16,6 +16,11 @@ class TaxonomyVocabularyArgumentTest extends TaxonomyTestBase {
    */
   public static $modules = ['taxonomy', 'taxonomy_test_views', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TermDisplayConfigurableTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TermDisplayConfigurableTest.php
index 5c89c7fb2c27fecabb74d385f49098ba561413d3..e1a24aaef20804c88e9535505ae1103fdd5e5537 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TermDisplayConfigurableTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TermDisplayConfigurableTest.php
@@ -9,6 +9,11 @@
  */
 class TermDisplayConfigurableTest extends TaxonomyTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/taxonomy/tests/src/Functional/Views/TermNameFieldTest.php b/core/modules/taxonomy/tests/src/Functional/Views/TermNameFieldTest.php
index 6fbe0c0b2b5d33efdb17f47a1cb7373eacb53fc2..baad381aae8f704c8a975b2d7034dee9065b30ae 100644
--- a/core/modules/taxonomy/tests/src/Functional/Views/TermNameFieldTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/Views/TermNameFieldTest.php
@@ -18,6 +18,11 @@ class TermNameFieldTest extends TaxonomyTestBase {
    */
   public static $testViews = ['test_taxonomy_term_name'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests term name field plugin functionality.
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/VocabularyLanguageTest.php b/core/modules/taxonomy/tests/src/Functional/VocabularyLanguageTest.php
index c94d64e287d80ce3edb31d0f7f2c141332f05b65..17a096b2cbe6401ae234e7e2645b1893615706f9 100644
--- a/core/modules/taxonomy/tests/src/Functional/VocabularyLanguageTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/VocabularyLanguageTest.php
@@ -14,6 +14,11 @@ class VocabularyLanguageTest extends TaxonomyTestBase {
 
   public static $modules = ['language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/taxonomy/tests/src/Functional/VocabularyPermissionsTest.php b/core/modules/taxonomy/tests/src/Functional/VocabularyPermissionsTest.php
index bb94a96da67a50761c6e71b82dd26d58f399d740..174feab7f75b487cdd6bc411a0f43e8f591139f0 100644
--- a/core/modules/taxonomy/tests/src/Functional/VocabularyPermissionsTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/VocabularyPermissionsTest.php
@@ -18,6 +18,11 @@ class VocabularyPermissionsTest extends TaxonomyTestBase {
    */
   public static $modules = ['help'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/taxonomy/tests/src/Functional/VocabularySerializationTest.php b/core/modules/taxonomy/tests/src/Functional/VocabularySerializationTest.php
index b9aba8a7989e1509ff42ed273c57bd34a88252d6..bb43476cf27a56c8f50eec1535e78c7774b5206d 100644
--- a/core/modules/taxonomy/tests/src/Functional/VocabularySerializationTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/VocabularySerializationTest.php
@@ -23,6 +23,11 @@ class VocabularySerializationTest extends BrowserTestBase {
    */
   public static $modules = ['taxonomy', 'vocabulary_serialization_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/VocabularyTranslationTest.php b/core/modules/taxonomy/tests/src/Functional/VocabularyTranslationTest.php
index aa98ac33300b6b83b304b7d3f1c744666297c328..16ba9c646540445151ee80f76b9afe68fb2f2692 100644
--- a/core/modules/taxonomy/tests/src/Functional/VocabularyTranslationTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/VocabularyTranslationTest.php
@@ -14,6 +14,11 @@ class VocabularyTranslationTest extends TaxonomyTestBase {
    */
   public static $modules = ['content_translation', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/taxonomy/tests/src/Functional/VocabularyUiTest.php b/core/modules/taxonomy/tests/src/Functional/VocabularyUiTest.php
index 7cddcc58199a09cbedb2d0d421312ac4bb176813..1a738958dbf3bdd178688be1a0064c19be5c8aed 100644
--- a/core/modules/taxonomy/tests/src/Functional/VocabularyUiTest.php
+++ b/core/modules/taxonomy/tests/src/Functional/VocabularyUiTest.php
@@ -19,6 +19,11 @@ class VocabularyUiTest extends TaxonomyTestBase {
    */
   protected $vocabulary;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $this->drupalLogin($this->drupalCreateUser(['administer taxonomy']));
diff --git a/core/modules/telephone/tests/src/Functional/TelephoneFieldTest.php b/core/modules/telephone/tests/src/Functional/TelephoneFieldTest.php
index 843bf4472b49e1d979b49c8bab105431823bd9e4..40607d2359b32ef78443ad187bbd5f261a9f6b4a 100644
--- a/core/modules/telephone/tests/src/Functional/TelephoneFieldTest.php
+++ b/core/modules/telephone/tests/src/Functional/TelephoneFieldTest.php
@@ -24,6 +24,11 @@ class TelephoneFieldTest extends BrowserTestBase {
     'telephone',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to create articles.
    *
diff --git a/core/modules/text/tests/src/Functional/TextFieldTest.php b/core/modules/text/tests/src/Functional/TextFieldTest.php
index 489d70fc593bba4ca19fd619ff3abc9769238c0a..3eba8c7e574b2c5eedee30343ab2c5a6746493df 100644
--- a/core/modules/text/tests/src/Functional/TextFieldTest.php
+++ b/core/modules/text/tests/src/Functional/TextFieldTest.php
@@ -28,6 +28,11 @@ class TextFieldTest extends StringFieldTest {
    */
   protected $adminUser;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/text/tests/src/Functional/TextRequiredSummaryUpdateTest.php b/core/modules/text/tests/src/Functional/TextRequiredSummaryUpdateTest.php
index 62b22ef26377dae90ebe12ca3bb347c1ea1cb102..ba94af28cc63e7c72109600fd367f1fe97258a67 100644
--- a/core/modules/text/tests/src/Functional/TextRequiredSummaryUpdateTest.php
+++ b/core/modules/text/tests/src/Functional/TextRequiredSummaryUpdateTest.php
@@ -14,6 +14,11 @@
  */
 class TextRequiredSummaryUpdateTest extends UpdatePathTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/text/tests/src/FunctionalJavascript/TextareaWithSummaryTest.php b/core/modules/text/tests/src/FunctionalJavascript/TextareaWithSummaryTest.php
index 88153abce5b43787694b5352d99e8b3fb8fb90bd..9d939eead4e41da65a43f2db860066d34ff871b0 100644
--- a/core/modules/text/tests/src/FunctionalJavascript/TextareaWithSummaryTest.php
+++ b/core/modules/text/tests/src/FunctionalJavascript/TextareaWithSummaryTest.php
@@ -17,6 +17,11 @@ class TextareaWithSummaryTest extends WebDriverTestBase {
    */
   public static $modules = ['text', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/toolbar/tests/src/Functional/ToolbarAdminMenuTest.php b/core/modules/toolbar/tests/src/Functional/ToolbarAdminMenuTest.php
index fd27b4ba3db077ec76787f347ca16c0d7ae658ed..7260d2395796203afc08b8948669eb5de477d1e5 100644
--- a/core/modules/toolbar/tests/src/Functional/ToolbarAdminMenuTest.php
+++ b/core/modules/toolbar/tests/src/Functional/ToolbarAdminMenuTest.php
@@ -56,6 +56,11 @@ class ToolbarAdminMenuTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'block', 'menu_ui', 'user', 'taxonomy', 'toolbar', 'language', 'test_page_test', 'locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/toolbar/tests/src/Functional/ToolbarCacheContextsTest.php b/core/modules/toolbar/tests/src/Functional/ToolbarCacheContextsTest.php
index 0232545473217c8d7fa4f5c3f34db24161b86fac..8b564cca07d6185b3fbeaac545710a5ca1476e0f 100644
--- a/core/modules/toolbar/tests/src/Functional/ToolbarCacheContextsTest.php
+++ b/core/modules/toolbar/tests/src/Functional/ToolbarCacheContextsTest.php
@@ -23,6 +23,11 @@ class ToolbarCacheContextsTest extends BrowserTestBase {
    */
   public static $modules = ['toolbar', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An authenticated user to use for testing.
    *
diff --git a/core/modules/toolbar/tests/src/Functional/ToolbarHookToolbarTest.php b/core/modules/toolbar/tests/src/Functional/ToolbarHookToolbarTest.php
index f3d3ce6118db27e2dac1d28dfc5f1fd07f7cdbd8..3153bbe21600c594b1af14ee4ece224f9aabc199 100644
--- a/core/modules/toolbar/tests/src/Functional/ToolbarHookToolbarTest.php
+++ b/core/modules/toolbar/tests/src/Functional/ToolbarHookToolbarTest.php
@@ -25,6 +25,11 @@ class ToolbarHookToolbarTest extends BrowserTestBase {
    */
   public static $modules = ['toolbar', 'toolbar_test', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/toolbar/tests/src/Functional/ToolbarMenuTranslationTest.php b/core/modules/toolbar/tests/src/Functional/ToolbarMenuTranslationTest.php
index 995d49ee386991a9ced937ac1cf64e007c679e07..57336e04b2f89c31baaa305e3f3f6bf4c759146c 100644
--- a/core/modules/toolbar/tests/src/Functional/ToolbarMenuTranslationTest.php
+++ b/core/modules/toolbar/tests/src/Functional/ToolbarMenuTranslationTest.php
@@ -25,6 +25,11 @@ class ToolbarMenuTranslationTest extends BrowserTestBase {
    */
   public static $modules = ['toolbar', 'toolbar_test', 'locale', 'locale_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
index fd163985e75068ffcde1865bae949ea11d8bccd4..8ee38bdb16a5cb2cae53e8f44c07f93e70a5510f 100644
--- a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
+++ b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
@@ -16,6 +16,11 @@ class ToolbarIntegrationTest extends WebDriverTestBase {
    */
   public static $modules = ['toolbar', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if the toolbar can be toggled with JavaScript.
    */
diff --git a/core/modules/tour/tests/src/Functional/Hal/TourHalJsonAnonTest.php b/core/modules/tour/tests/src/Functional/Hal/TourHalJsonAnonTest.php
index 1461fc1a88d9ba0847c65b558f4d087d0feb352c..b4e37290cd080ffff190ec028ab94adc9caa35f1 100644
--- a/core/modules/tour/tests/src/Functional/Hal/TourHalJsonAnonTest.php
+++ b/core/modules/tour/tests/src/Functional/Hal/TourHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class TourHalJsonAnonTest extends TourResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/tour/tests/src/Functional/Hal/TourHalJsonBasicAuthTest.php b/core/modules/tour/tests/src/Functional/Hal/TourHalJsonBasicAuthTest.php
index c79f55e48e671bfaafb8ce1a759c9f793a95833b..6d70a323db77fdb07c24cb8a6e1855b7d06c00f9 100644
--- a/core/modules/tour/tests/src/Functional/Hal/TourHalJsonBasicAuthTest.php
+++ b/core/modules/tour/tests/src/Functional/Hal/TourHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class TourHalJsonBasicAuthTest extends TourResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/tour/tests/src/Functional/Hal/TourHalJsonCookieTest.php b/core/modules/tour/tests/src/Functional/Hal/TourHalJsonCookieTest.php
index 6a7737db0810e53edd8bd225599226f60b2d6537..43ea4ea1b4c24a0d3917f35e2aa6cacd688e4ebf 100644
--- a/core/modules/tour/tests/src/Functional/Hal/TourHalJsonCookieTest.php
+++ b/core/modules/tour/tests/src/Functional/Hal/TourHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class TourHalJsonCookieTest extends TourResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/tour/tests/src/Functional/Rest/TourJsonAnonTest.php b/core/modules/tour/tests/src/Functional/Rest/TourJsonAnonTest.php
index 530fbe70b86c67c275eb95661178466310a65997..0a171f248572769eeb0b62ed4eee46b89801f021 100644
--- a/core/modules/tour/tests/src/Functional/Rest/TourJsonAnonTest.php
+++ b/core/modules/tour/tests/src/Functional/Rest/TourJsonAnonTest.php
@@ -21,4 +21,9 @@ class TourJsonAnonTest extends TourResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/tour/tests/src/Functional/Rest/TourJsonBasicAuthTest.php b/core/modules/tour/tests/src/Functional/Rest/TourJsonBasicAuthTest.php
index fb1ff6995c4b9a4463e2e5f785128cb06271a245..bad2b4112b1d594e5d7f032454c5d2507c2d1bb1 100644
--- a/core/modules/tour/tests/src/Functional/Rest/TourJsonBasicAuthTest.php
+++ b/core/modules/tour/tests/src/Functional/Rest/TourJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class TourJsonBasicAuthTest extends TourResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/tour/tests/src/Functional/Rest/TourJsonCookieTest.php b/core/modules/tour/tests/src/Functional/Rest/TourJsonCookieTest.php
index c173395b3a6a542ffc4072b0baa54014b7c402cb..f124c5ce331a71bfd7b828050165f80840f373a0 100644
--- a/core/modules/tour/tests/src/Functional/Rest/TourJsonCookieTest.php
+++ b/core/modules/tour/tests/src/Functional/Rest/TourJsonCookieTest.php
@@ -26,4 +26,9 @@ class TourJsonCookieTest extends TourResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/tour/tests/src/Functional/Rest/TourXmlAnonTest.php b/core/modules/tour/tests/src/Functional/Rest/TourXmlAnonTest.php
index 8f44c87bbdd3a8794929601dfcdbd0ae92fea840..416c3b353b41eaaffef8be24545d3af36d6bda48 100644
--- a/core/modules/tour/tests/src/Functional/Rest/TourXmlAnonTest.php
+++ b/core/modules/tour/tests/src/Functional/Rest/TourXmlAnonTest.php
@@ -23,4 +23,9 @@ class TourXmlAnonTest extends TourResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/tour/tests/src/Functional/Rest/TourXmlBasicAuthTest.php b/core/modules/tour/tests/src/Functional/Rest/TourXmlBasicAuthTest.php
index 618b41defdd7df7bede0b0b5a1e256816e01b64a..fca59e3ae90179d31329f6f36e9e438b432137bc 100644
--- a/core/modules/tour/tests/src/Functional/Rest/TourXmlBasicAuthTest.php
+++ b/core/modules/tour/tests/src/Functional/Rest/TourXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class TourXmlBasicAuthTest extends TourResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/tour/tests/src/Functional/Rest/TourXmlCookieTest.php b/core/modules/tour/tests/src/Functional/Rest/TourXmlCookieTest.php
index 4d65bfff3db288f04dc9128a0335b507ce32aa5a..4fee143b932a41b278598fd7b016681f8d01f8f1 100644
--- a/core/modules/tour/tests/src/Functional/Rest/TourXmlCookieTest.php
+++ b/core/modules/tour/tests/src/Functional/Rest/TourXmlCookieTest.php
@@ -28,4 +28,9 @@ class TourXmlCookieTest extends TourResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/tour/tests/src/Functional/TourCacheTagsTest.php b/core/modules/tour/tests/src/Functional/TourCacheTagsTest.php
index daed6fa292b3904d14479e80489cc36efd2b456d..d85e9a56b2a34216efc8dc79bb3243fc5224f0c4 100644
--- a/core/modules/tour/tests/src/Functional/TourCacheTagsTest.php
+++ b/core/modules/tour/tests/src/Functional/TourCacheTagsTest.php
@@ -20,6 +20,11 @@ class TourCacheTagsTest extends PageCacheTagsTestBase {
    */
   public static $modules = ['tour', 'tour_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/tour/tests/src/Functional/TourHelpPageTest.php b/core/modules/tour/tests/src/Functional/TourHelpPageTest.php
index ad60df104f207b4034e8a83c56a13cef87c24413..a88da72cb9aa0acfcf7bc5f158828aeffea483a7 100644
--- a/core/modules/tour/tests/src/Functional/TourHelpPageTest.php
+++ b/core/modules/tour/tests/src/Functional/TourHelpPageTest.php
@@ -18,6 +18,11 @@ class TourHelpPageTest extends BrowserTestBase {
    */
   public static $modules = ['help', 'tour', 'locale', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * User that can access tours and help.
    *
diff --git a/core/modules/tour/tests/src/Functional/TourTest.php b/core/modules/tour/tests/src/Functional/TourTest.php
index b20b1b8779ec91eea384fa207a592ca554f4eb5f..cba8ff2801e20e9793906314c6ec320f845f9738 100644
--- a/core/modules/tour/tests/src/Functional/TourTest.php
+++ b/core/modules/tour/tests/src/Functional/TourTest.php
@@ -20,6 +20,11 @@ class TourTest extends TourTestBasic {
    */
   public static $modules = ['block', 'tour', 'locale', 'language', 'tour_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The permissions required for a logged in user to test tour tips.
    *
diff --git a/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php b/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php
index 2b320ae4b6dfde17118310d8128ee9b3d45b7a71..990612d0beb8d2e8c8153ab8b8cdba324718ab9e 100644
--- a/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php
+++ b/core/modules/tracker/tests/src/Functional/TrackerNodeAccessTest.php
@@ -23,6 +23,11 @@ class TrackerNodeAccessTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'comment', 'tracker', 'node_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     node_access_rebuild();
diff --git a/core/modules/tracker/tests/src/Functional/TrackerTest.php b/core/modules/tracker/tests/src/Functional/TrackerTest.php
index 63d1cb2f426d746ea49ba0589e099621263f2959..3d907212c8931def493c4994efdddf2c54546612 100644
--- a/core/modules/tracker/tests/src/Functional/TrackerTest.php
+++ b/core/modules/tracker/tests/src/Functional/TrackerTest.php
@@ -31,6 +31,11 @@ class TrackerTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'comment', 'tracker', 'history', 'node_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The main user for testing.
    *
diff --git a/core/modules/update/tests/src/Functional/FileTransferAuthorizeFormTest.php b/core/modules/update/tests/src/Functional/FileTransferAuthorizeFormTest.php
index d768b06d81839a80d10a52b29f5bceebf6b48a37..f2c82a0bb2ce0cbdf4409edac1d4c9cd18ca96ac 100644
--- a/core/modules/update/tests/src/Functional/FileTransferAuthorizeFormTest.php
+++ b/core/modules/update/tests/src/Functional/FileTransferAuthorizeFormTest.php
@@ -16,6 +16,11 @@ class FileTransferAuthorizeFormTest extends UpdateTestBase {
    */
   public static $modules = ['update', 'update_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $admin_user = $this->drupalCreateUser(['administer modules', 'administer software updates', 'administer site configuration']);
diff --git a/core/modules/update/tests/src/Functional/UpdateContribTest.php b/core/modules/update/tests/src/Functional/UpdateContribTest.php
index 5db38ce3457b9f354129c9edfb1c35bebd92e382..feabdcfd8bbdd386e1757a8555b25d2ae26a96bd 100644
--- a/core/modules/update/tests/src/Functional/UpdateContribTest.php
+++ b/core/modules/update/tests/src/Functional/UpdateContribTest.php
@@ -21,6 +21,11 @@ class UpdateContribTest extends UpdateTestBase {
    */
   public static $modules = ['update_test', 'update', 'aaa_update_test', 'bbb_update_test', 'ccc_update_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $admin_user = $this->drupalCreateUser(['administer site configuration']);
diff --git a/core/modules/update/tests/src/Functional/UpdateCoreTest.php b/core/modules/update/tests/src/Functional/UpdateCoreTest.php
index dec4022615abc8718c4f582026588593be2e9cbc..d0b0b93301974f0a2a09ea18c091f8d44666e5a9 100644
--- a/core/modules/update/tests/src/Functional/UpdateCoreTest.php
+++ b/core/modules/update/tests/src/Functional/UpdateCoreTest.php
@@ -23,6 +23,11 @@ class UpdateCoreTest extends UpdateTestBase {
    */
   public static $modules = ['update_test', 'update', 'language', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $admin_user = $this->drupalCreateUser(['administer site configuration', 'administer modules', 'administer themes']);
diff --git a/core/modules/update/tests/src/Functional/UpdateUploadTest.php b/core/modules/update/tests/src/Functional/UpdateUploadTest.php
index 74cfc5770ba0a72f3ec3c295e9bdb12bbc65cfb9..a05e8a35a3b0c10a14bc2952c146fdd7a5e0be07 100644
--- a/core/modules/update/tests/src/Functional/UpdateUploadTest.php
+++ b/core/modules/update/tests/src/Functional/UpdateUploadTest.php
@@ -25,6 +25,11 @@ class UpdateUploadTest extends UpdateTestBase {
    */
   public static $modules = ['update', 'update_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     $admin_user = $this->drupalCreateUser(['administer modules', 'administer software updates', 'administer site configuration']);
diff --git a/core/modules/user/tests/src/Functional/AccessRoleUITest.php b/core/modules/user/tests/src/Functional/AccessRoleUITest.php
index d5346b1237ebfbd311b4f5f7318892f9a7cc2bd5..64615562b0dab12f4c83bea21fba35afde27772d 100644
--- a/core/modules/user/tests/src/Functional/AccessRoleUITest.php
+++ b/core/modules/user/tests/src/Functional/AccessRoleUITest.php
@@ -27,6 +27,11 @@ class AccessRoleUITest extends UITestBase {
    */
   public static $modules = ['user', 'user_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Hal/RoleHalJsonAnonTest.php b/core/modules/user/tests/src/Functional/Hal/RoleHalJsonAnonTest.php
index a08a1d094a89e3b2cc66e14c3ecb63bfb0f33403..fa60f6e6a168ff0ef74477dd4eae0db0e54ef4da 100644
--- a/core/modules/user/tests/src/Functional/Hal/RoleHalJsonAnonTest.php
+++ b/core/modules/user/tests/src/Functional/Hal/RoleHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class RoleHalJsonAnonTest extends RoleResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Hal/RoleHalJsonBasicAuthTest.php b/core/modules/user/tests/src/Functional/Hal/RoleHalJsonBasicAuthTest.php
index 1e613e5d73fc9e9d77d34f220949d9df25f444ec..5e270312080e3a384cefdb88a457f424cacfc3d2 100644
--- a/core/modules/user/tests/src/Functional/Hal/RoleHalJsonBasicAuthTest.php
+++ b/core/modules/user/tests/src/Functional/Hal/RoleHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class RoleHalJsonBasicAuthTest extends RoleResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Hal/RoleHalJsonCookieTest.php b/core/modules/user/tests/src/Functional/Hal/RoleHalJsonCookieTest.php
index 0074e0516cb1be905693381f2c41fda95300fb49..deaccbdc9632cef5078ce0cad2589beeb21fa84a 100644
--- a/core/modules/user/tests/src/Functional/Hal/RoleHalJsonCookieTest.php
+++ b/core/modules/user/tests/src/Functional/Hal/RoleHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class RoleHalJsonCookieTest extends RoleResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Hal/UserHalJsonAnonTest.php b/core/modules/user/tests/src/Functional/Hal/UserHalJsonAnonTest.php
index b33c6868bcbed3758a7681fc9b85f4ed93cfe089..18baea1d0b28d720bfa1ae623d4185c1e51cdd54 100644
--- a/core/modules/user/tests/src/Functional/Hal/UserHalJsonAnonTest.php
+++ b/core/modules/user/tests/src/Functional/Hal/UserHalJsonAnonTest.php
@@ -19,6 +19,11 @@ class UserHalJsonAnonTest extends UserResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Hal/UserHalJsonBasicAuthTest.php b/core/modules/user/tests/src/Functional/Hal/UserHalJsonBasicAuthTest.php
index 7da859e0608905dc301cf29c369225db27b78e63..0d34b132ae705b46788c89b985fc5b3247d79ab4 100644
--- a/core/modules/user/tests/src/Functional/Hal/UserHalJsonBasicAuthTest.php
+++ b/core/modules/user/tests/src/Functional/Hal/UserHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class UserHalJsonBasicAuthTest extends UserHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Hal/UserHalJsonCookieTest.php b/core/modules/user/tests/src/Functional/Hal/UserHalJsonCookieTest.php
index e5e785cc80a6d5fec474091ce147ee425fcedc28..2945db5a6ed7fe23ab1a3f03b0d95ab798c6807e 100644
--- a/core/modules/user/tests/src/Functional/Hal/UserHalJsonCookieTest.php
+++ b/core/modules/user/tests/src/Functional/Hal/UserHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class UserHalJsonCookieTest extends UserHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/user/tests/src/Functional/Rest/RoleJsonAnonTest.php b/core/modules/user/tests/src/Functional/Rest/RoleJsonAnonTest.php
index 16e3e03eea60fcd1438046df11fac93d3eac90f1..7cf62c707b64d55917bbb73745deb73e40d4e815 100644
--- a/core/modules/user/tests/src/Functional/Rest/RoleJsonAnonTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/RoleJsonAnonTest.php
@@ -21,4 +21,9 @@ class RoleJsonAnonTest extends RoleResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/user/tests/src/Functional/Rest/RoleJsonBasicAuthTest.php b/core/modules/user/tests/src/Functional/Rest/RoleJsonBasicAuthTest.php
index 79d16cb90b76b12643de94c337484179b27b23e6..39993113cd01f374a336f0284dab11f391403bfd 100644
--- a/core/modules/user/tests/src/Functional/Rest/RoleJsonBasicAuthTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/RoleJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class RoleJsonBasicAuthTest extends RoleResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Rest/RoleJsonCookieTest.php b/core/modules/user/tests/src/Functional/Rest/RoleJsonCookieTest.php
index 6c31ab0041405a5457e4c628eed20b27ca7e1fc9..03f517fa4c182054479e6b3ef4584137d78f15be 100644
--- a/core/modules/user/tests/src/Functional/Rest/RoleJsonCookieTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/RoleJsonCookieTest.php
@@ -26,4 +26,9 @@ class RoleJsonCookieTest extends RoleResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/user/tests/src/Functional/Rest/RoleXmlAnonTest.php b/core/modules/user/tests/src/Functional/Rest/RoleXmlAnonTest.php
index 14910a62026db38e5a80dce6cad165f416b35680..a3e2e0a5b5f019ac5677931827a4cc0ad1266453 100644
--- a/core/modules/user/tests/src/Functional/Rest/RoleXmlAnonTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/RoleXmlAnonTest.php
@@ -23,4 +23,9 @@ class RoleXmlAnonTest extends RoleResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/user/tests/src/Functional/Rest/RoleXmlBasicAuthTest.php b/core/modules/user/tests/src/Functional/Rest/RoleXmlBasicAuthTest.php
index fa98edd47c01492af08db0bc726ecc3d0cd3b04b..4fda554c24837cbae83c5c6457affeacab6401a8 100644
--- a/core/modules/user/tests/src/Functional/Rest/RoleXmlBasicAuthTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/RoleXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class RoleXmlBasicAuthTest extends RoleResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Rest/RoleXmlCookieTest.php b/core/modules/user/tests/src/Functional/Rest/RoleXmlCookieTest.php
index 5e04d7c35064656b59a100e5e514e1f7c65e878e..8767934394a5237039f40d5e73c1009d60242880 100644
--- a/core/modules/user/tests/src/Functional/Rest/RoleXmlCookieTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/RoleXmlCookieTest.php
@@ -28,4 +28,9 @@ class RoleXmlCookieTest extends RoleResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/user/tests/src/Functional/Rest/UserJsonAnonTest.php b/core/modules/user/tests/src/Functional/Rest/UserJsonAnonTest.php
index 5b7e09e2e3500f23b8eeb8f4eb87f1e0071667af..ba2b0b392d8e4219c0559513713d84c60ef5d3e3 100644
--- a/core/modules/user/tests/src/Functional/Rest/UserJsonAnonTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/UserJsonAnonTest.php
@@ -21,4 +21,9 @@ class UserJsonAnonTest extends UserResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/user/tests/src/Functional/Rest/UserJsonBasicAuthTest.php b/core/modules/user/tests/src/Functional/Rest/UserJsonBasicAuthTest.php
index 7a1ea2674e5feab3f9505ecb209e13db4842d39e..15ba10bc77646fb30a208c5c6283dcfed7f2aa70 100644
--- a/core/modules/user/tests/src/Functional/Rest/UserJsonBasicAuthTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/UserJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class UserJsonBasicAuthTest extends UserResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Rest/UserJsonCookieTest.php b/core/modules/user/tests/src/Functional/Rest/UserJsonCookieTest.php
index 6e325d8b2ba77d97f665fcdba1aaad3dfc3a4ee8..21a46cd06fd90159d385691e583f9ed0e325c24c 100644
--- a/core/modules/user/tests/src/Functional/Rest/UserJsonCookieTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/UserJsonCookieTest.php
@@ -26,4 +26,9 @@ class UserJsonCookieTest extends UserResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/user/tests/src/Functional/Rest/UserXmlAnonTest.php b/core/modules/user/tests/src/Functional/Rest/UserXmlAnonTest.php
index 4629192ce0a17c033c8581b3a2a1d9e8fe894874..3340729364aec1dc9f2ea1529e8c76a2e95e0623 100644
--- a/core/modules/user/tests/src/Functional/Rest/UserXmlAnonTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/UserXmlAnonTest.php
@@ -23,6 +23,11 @@ class UserXmlAnonTest extends UserResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Rest/UserXmlBasicAuthTest.php b/core/modules/user/tests/src/Functional/Rest/UserXmlBasicAuthTest.php
index fc985980c3f4c8a18769e0746cbf2f1840cfcc31..f213e1b5d0065a671aa95af34e17676bf1cd9f43 100644
--- a/core/modules/user/tests/src/Functional/Rest/UserXmlBasicAuthTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/UserXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class UserXmlBasicAuthTest extends UserResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/Rest/UserXmlCookieTest.php b/core/modules/user/tests/src/Functional/Rest/UserXmlCookieTest.php
index 9a0c724f4d76001f5254acae96ed93870f1077cd..6015e2df5530677d021e755cb4ada6225311203c 100644
--- a/core/modules/user/tests/src/Functional/Rest/UserXmlCookieTest.php
+++ b/core/modules/user/tests/src/Functional/Rest/UserXmlCookieTest.php
@@ -28,6 +28,11 @@ class UserXmlCookieTest extends UserResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/RestRegisterUserTest.php b/core/modules/user/tests/src/Functional/RestRegisterUserTest.php
index 5f06214e03f578c1476cc728b808997ff44faaca..990892a6f3a843af1958f5990f308e6e55c3d13f 100644
--- a/core/modules/user/tests/src/Functional/RestRegisterUserTest.php
+++ b/core/modules/user/tests/src/Functional/RestRegisterUserTest.php
@@ -22,6 +22,11 @@ class RestRegisterUserTest extends ResourceTestBase {
     getMails as drupalGetMails;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/UserAccountLinksTest.php b/core/modules/user/tests/src/Functional/UserAccountLinksTest.php
index c09fc34daffce51ddb3c34c6611456cdd255d187..691695a0904b3cb75b729a7e6a84ca34c5bb8c43 100644
--- a/core/modules/user/tests/src/Functional/UserAccountLinksTest.php
+++ b/core/modules/user/tests/src/Functional/UserAccountLinksTest.php
@@ -18,6 +18,11 @@ class UserAccountLinksTest extends BrowserTestBase {
    */
   public static $modules = ['menu_ui', 'block', 'test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/UserAdminLanguageTest.php b/core/modules/user/tests/src/Functional/UserAdminLanguageTest.php
index 5e9f3ee465062d89cce3bc6ab8d7a3fc811f1e02..4d5ef5b6028228ff45577853edce451538e852fc 100644
--- a/core/modules/user/tests/src/Functional/UserAdminLanguageTest.php
+++ b/core/modules/user/tests/src/Functional/UserAdminLanguageTest.php
@@ -33,6 +33,11 @@ class UserAdminLanguageTest extends BrowserTestBase {
    */
   public static $modules = ['user', 'language', 'language_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
     // User to add and remove language.
diff --git a/core/modules/user/tests/src/Functional/UserAdminListingTest.php b/core/modules/user/tests/src/Functional/UserAdminListingTest.php
index 1617d14eb4e43a70ded09d01b8d08adb496b479e..ec4375a143be0f4a3ef72264b8a084a3a3f928da 100644
--- a/core/modules/user/tests/src/Functional/UserAdminListingTest.php
+++ b/core/modules/user/tests/src/Functional/UserAdminListingTest.php
@@ -13,6 +13,11 @@
  */
 class UserAdminListingTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests the listing.
    */
diff --git a/core/modules/user/tests/src/Functional/UserAdminTest.php b/core/modules/user/tests/src/Functional/UserAdminTest.php
index 298d41493eafbf58400f1cb15d36c323dab92262..991f99304d693c74ea7ce08e944f5c1a2e3db92d 100644
--- a/core/modules/user/tests/src/Functional/UserAdminTest.php
+++ b/core/modules/user/tests/src/Functional/UserAdminTest.php
@@ -25,6 +25,11 @@ class UserAdminTest extends BrowserTestBase {
    */
   public static $modules = ['taxonomy', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Registers a user and deletes it.
    */
diff --git a/core/modules/user/tests/src/Functional/UserBlocksTest.php b/core/modules/user/tests/src/Functional/UserBlocksTest.php
index f308283dee90e73442b7c41223822c15e107c5d3..0f9b82b8fb6840114a780b6d2de1de8da6ae12f5 100644
--- a/core/modules/user/tests/src/Functional/UserBlocksTest.php
+++ b/core/modules/user/tests/src/Functional/UserBlocksTest.php
@@ -21,6 +21,11 @@ class UserBlocksTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A user with the 'administer blocks' permission.
    *
diff --git a/core/modules/user/tests/src/Functional/UserCacheTagsTest.php b/core/modules/user/tests/src/Functional/UserCacheTagsTest.php
index c9ab91fac71a82851713587045ae30306611c369..a65b34db7e730c8c9c6433c83317c763c3ff3da3 100644
--- a/core/modules/user/tests/src/Functional/UserCacheTagsTest.php
+++ b/core/modules/user/tests/src/Functional/UserCacheTagsTest.php
@@ -19,6 +19,11 @@ class UserCacheTagsTest extends EntityWithUriCacheTagsTestBase {
    */
   public static $modules = ['user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/UserCancelTest.php b/core/modules/user/tests/src/Functional/UserCancelTest.php
index 365be54f48c91de4f31071523690437973498872..65632c03a0bf75845ed0af4d7ff7db123fa7fd78 100644
--- a/core/modules/user/tests/src/Functional/UserCancelTest.php
+++ b/core/modules/user/tests/src/Functional/UserCancelTest.php
@@ -24,6 +24,11 @@ class UserCancelTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'comment'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/user/tests/src/Functional/UserCreateFailMailTest.php b/core/modules/user/tests/src/Functional/UserCreateFailMailTest.php
index 38f2514a496f52f32d4d520aa3da72042681bf28..96323279a314caf852f516638893f280726c1155 100644
--- a/core/modules/user/tests/src/Functional/UserCreateFailMailTest.php
+++ b/core/modules/user/tests/src/Functional/UserCreateFailMailTest.php
@@ -18,6 +18,11 @@ class UserCreateFailMailTest extends BrowserTestBase {
    */
   public static $modules = ['system_mail_failure_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the create user administration page.
    */
diff --git a/core/modules/user/tests/src/Functional/UserCreateTest.php b/core/modules/user/tests/src/Functional/UserCreateTest.php
index 8c281111459dbd236dd1ec3c4b3328be3b671f30..fceb1af1d66a594b637978a247f42ad48fa4cf3b 100644
--- a/core/modules/user/tests/src/Functional/UserCreateTest.php
+++ b/core/modules/user/tests/src/Functional/UserCreateTest.php
@@ -25,6 +25,11 @@ class UserCreateTest extends BrowserTestBase {
    */
   public static $modules = ['image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Create a user through the administration interface and ensure that it
    * displays in the user list.
diff --git a/core/modules/user/tests/src/Functional/UserEditTest.php b/core/modules/user/tests/src/Functional/UserEditTest.php
index eba49bab596de1536c51cf16178e3c2424190db9..6a71927a96cc4b6b635cfa6924affba12bed0613 100644
--- a/core/modules/user/tests/src/Functional/UserEditTest.php
+++ b/core/modules/user/tests/src/Functional/UserEditTest.php
@@ -12,6 +12,11 @@
  */
 class UserEditTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test user edit page.
    */
diff --git a/core/modules/user/tests/src/Functional/UserEditedOwnAccountTest.php b/core/modules/user/tests/src/Functional/UserEditedOwnAccountTest.php
index 75f654297b8de97f250e48d8fc62cb756db3c6d9..4fe8d0a6baa2edb294d1b1d0b52f16c168931b47 100644
--- a/core/modules/user/tests/src/Functional/UserEditedOwnAccountTest.php
+++ b/core/modules/user/tests/src/Functional/UserEditedOwnAccountTest.php
@@ -12,6 +12,11 @@
  */
 class UserEditedOwnAccountTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testUserEditedOwnAccount() {
     // Change account setting 'Who can register accounts?' to Administrators
     // only.
diff --git a/core/modules/user/tests/src/Functional/UserLanguageCreationTest.php b/core/modules/user/tests/src/Functional/UserLanguageCreationTest.php
index 6f493418b2082417e81f0d2c23605534772d9344..85e39589db7d13c6a30b7493627149cc3214bfcc 100644
--- a/core/modules/user/tests/src/Functional/UserLanguageCreationTest.php
+++ b/core/modules/user/tests/src/Functional/UserLanguageCreationTest.php
@@ -20,6 +20,11 @@ class UserLanguageCreationTest extends BrowserTestBase {
    */
   public static $modules = ['user', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Functional test for language handling during user creation.
    */
diff --git a/core/modules/user/tests/src/Functional/UserLanguageTest.php b/core/modules/user/tests/src/Functional/UserLanguageTest.php
index 0e6c0f1a75db0836329b064a2e04fc0df25f1fd8..d221a61c1eb6d80111b65b5be6d78012d53d6368 100644
--- a/core/modules/user/tests/src/Functional/UserLanguageTest.php
+++ b/core/modules/user/tests/src/Functional/UserLanguageTest.php
@@ -19,6 +19,11 @@ class UserLanguageTest extends BrowserTestBase {
    */
   public static $modules = ['user', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test if user can change their default language.
    */
diff --git a/core/modules/user/tests/src/Functional/UserLoginHttpTest.php b/core/modules/user/tests/src/Functional/UserLoginHttpTest.php
index 47287810e01c884be8f169be901c3328c8ab612c..0402f6280646ad80827b950aeedda14e129c3d04 100644
--- a/core/modules/user/tests/src/Functional/UserLoginHttpTest.php
+++ b/core/modules/user/tests/src/Functional/UserLoginHttpTest.php
@@ -32,6 +32,11 @@ class UserLoginHttpTest extends BrowserTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The cookie jar.
    *
diff --git a/core/modules/user/tests/src/Functional/UserLoginTest.php b/core/modules/user/tests/src/Functional/UserLoginTest.php
index e9c88b106f658096a36379ea056c18ffdf615a82..e067915867e97ee0169a624fdabb6517ad28a4e4 100644
--- a/core/modules/user/tests/src/Functional/UserLoginTest.php
+++ b/core/modules/user/tests/src/Functional/UserLoginTest.php
@@ -13,6 +13,11 @@
  */
 class UserLoginTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests login with destination.
    */
diff --git a/core/modules/user/tests/src/Functional/UserPasswordResetTest.php b/core/modules/user/tests/src/Functional/UserPasswordResetTest.php
index 1bcbd1d1416d89253c0141d569237c295864b19e..650c2dfd01a566748eda87a4d7baa6d33c78f192 100644
--- a/core/modules/user/tests/src/Functional/UserPasswordResetTest.php
+++ b/core/modules/user/tests/src/Functional/UserPasswordResetTest.php
@@ -34,6 +34,11 @@ class UserPasswordResetTest extends PageCacheTagsTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/UserPermissionsTest.php b/core/modules/user/tests/src/Functional/UserPermissionsTest.php
index 14b0ca854e6ab34c3483d15fb209f513db1e945c..0eb453fc2678297d382a87a30887f1d86df33770 100644
--- a/core/modules/user/tests/src/Functional/UserPermissionsTest.php
+++ b/core/modules/user/tests/src/Functional/UserPermissionsTest.php
@@ -28,6 +28,11 @@ class UserPermissionsTest extends BrowserTestBase {
    */
   protected $rid;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp() {
     parent::setUp();
 
diff --git a/core/modules/user/tests/src/Functional/UserPictureTest.php b/core/modules/user/tests/src/Functional/UserPictureTest.php
index 3e853d70f9ec0eb08417227c440e9de7ac20dea9..efb785d6259c9a579f75ca68a393c865ea054300 100644
--- a/core/modules/user/tests/src/Functional/UserPictureTest.php
+++ b/core/modules/user/tests/src/Functional/UserPictureTest.php
@@ -30,6 +30,11 @@ class UserPictureTest extends BrowserTestBase {
    */
   protected $profile = 'standard';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * A regular user.
    *
diff --git a/core/modules/user/tests/src/Functional/UserRegistrationTest.php b/core/modules/user/tests/src/Functional/UserRegistrationTest.php
index 766baf304c2a2415c74afef1b1cc2b68aaac87bd..b72d7ec776febf7c54548124d25937496c42d0b5 100644
--- a/core/modules/user/tests/src/Functional/UserRegistrationTest.php
+++ b/core/modules/user/tests/src/Functional/UserRegistrationTest.php
@@ -24,6 +24,11 @@ class UserRegistrationTest extends BrowserTestBase {
    */
   public static $modules = ['field_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testRegistrationWithEmailVerification() {
     $config = $this->config('user.settings');
     // Require email verification.
diff --git a/core/modules/user/tests/src/Functional/UserRoleAdminTest.php b/core/modules/user/tests/src/Functional/UserRoleAdminTest.php
index c7e52135d695538f8a892c5f50b6897fe1fe5b42..ff529f83febfd12b6a07a94630721909f9e79543 100644
--- a/core/modules/user/tests/src/Functional/UserRoleAdminTest.php
+++ b/core/modules/user/tests/src/Functional/UserRoleAdminTest.php
@@ -27,6 +27,11 @@ class UserRoleAdminTest extends BrowserTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php b/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php
index 6cd80562c54019dd30188be197c6ef15d3c1e4d9..4a417494fc2df26b492c8562cc595e35f1b1ef47 100644
--- a/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php
+++ b/core/modules/user/tests/src/Functional/UserRolesAssignmentTest.php
@@ -17,6 +17,11 @@ protected function setUp() {
     $this->drupalLogin($admin_user);
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that a user can be assigned a role and that the role can be removed
    * again.
diff --git a/core/modules/user/tests/src/Functional/UserSearchTest.php b/core/modules/user/tests/src/Functional/UserSearchTest.php
index 24ab0afef558aab835593a7b47023bdb5310e78e..49fca33902e5e452ea03e4cecc082b23f005aaa6 100644
--- a/core/modules/user/tests/src/Functional/UserSearchTest.php
+++ b/core/modules/user/tests/src/Functional/UserSearchTest.php
@@ -19,6 +19,11 @@ class UserSearchTest extends BrowserTestBase {
    */
   public static $modules = ['search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testUserSearch() {
     // Verify that a user without 'administer users' permission cannot search
     // for users by email address. Additionally, ensure that the username has a
diff --git a/core/modules/user/tests/src/Functional/UserSubAdminTest.php b/core/modules/user/tests/src/Functional/UserSubAdminTest.php
index 029df0301acd654f95a82ff28069f0c22fc35f7a..0de619f2410b078bcffea74edfcefc1d9617e928 100644
--- a/core/modules/user/tests/src/Functional/UserSubAdminTest.php
+++ b/core/modules/user/tests/src/Functional/UserSubAdminTest.php
@@ -16,6 +16,11 @@ class UserSubAdminTest extends BrowserTestBase {
    */
   public static $modules = ['user_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test create and cancel forms as 'sub-admin'.
    */
diff --git a/core/modules/user/tests/src/Functional/UserTimeZoneTest.php b/core/modules/user/tests/src/Functional/UserTimeZoneTest.php
index ccf43253def6e4dae8e59fcb4ce5311ad05cf860..914fffa1c9aa804068c73a8031e071b933b4e435 100644
--- a/core/modules/user/tests/src/Functional/UserTimeZoneTest.php
+++ b/core/modules/user/tests/src/Functional/UserTimeZoneTest.php
@@ -19,6 +19,11 @@ class UserTimeZoneTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the display of dates and time when user-configurable time zones are set.
    */
diff --git a/core/modules/user/tests/src/Functional/UserTokenReplaceTest.php b/core/modules/user/tests/src/Functional/UserTokenReplaceTest.php
index 7ff6b31b8ea301c958c80414bb10305c9da589e1..1bc36a61510f6a5f6461d9c40d060e54b20c15fd 100644
--- a/core/modules/user/tests/src/Functional/UserTokenReplaceTest.php
+++ b/core/modules/user/tests/src/Functional/UserTokenReplaceTest.php
@@ -24,6 +24,11 @@ class UserTokenReplaceTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'user_hooks_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/user/tests/src/Functional/UserTranslationUITest.php b/core/modules/user/tests/src/Functional/UserTranslationUITest.php
index d087d528d719ab8dc2eaecf75b9c1ee4f662de8f..811a2f1744285324c3e9ae1102b37b97fc71aa4c 100644
--- a/core/modules/user/tests/src/Functional/UserTranslationUITest.php
+++ b/core/modules/user/tests/src/Functional/UserTranslationUITest.php
@@ -25,6 +25,11 @@ class UserTranslationUITest extends ContentTranslationUITestBase {
    */
   public static $modules = ['language', 'content_translation', 'user', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp() {
     $this->entityTypeId = 'user';
     $this->testLanguageSelector = FALSE;
diff --git a/core/modules/user/tests/src/Functional/Views/AccessRoleTest.php b/core/modules/user/tests/src/Functional/Views/AccessRoleTest.php
index 62bcd6c0f7cedf5e2116b2e47c18d8858052962a..4093fa45587db2c1bc1b1665a85c359b288d8d6c 100644
--- a/core/modules/user/tests/src/Functional/Views/AccessRoleTest.php
+++ b/core/modules/user/tests/src/Functional/Views/AccessRoleTest.php
@@ -25,6 +25,11 @@ class AccessRoleTest extends AccessTestBase {
    */
   public static $testViews = ['test_access_role'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests role access plugin.
    */
diff --git a/core/modules/user/tests/src/Functional/Views/BulkFormAccessTest.php b/core/modules/user/tests/src/Functional/Views/BulkFormAccessTest.php
index 5f613f3b16840c27e61188bae6f3649417373241..358ae1379137169a16b121e5b06f740bbe850cbd 100644
--- a/core/modules/user/tests/src/Functional/Views/BulkFormAccessTest.php
+++ b/core/modules/user/tests/src/Functional/Views/BulkFormAccessTest.php
@@ -21,6 +21,11 @@ class BulkFormAccessTest extends UserTestBase {
    */
   public static $modules = ['user_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/user/tests/src/Functional/Views/BulkFormTest.php b/core/modules/user/tests/src/Functional/Views/BulkFormTest.php
index a9ba63feed6b63a695347c1551adc4fcdb67bb7e..f7cb4f3fe04334ae70f25352c646c08ec0bd9d6d 100644
--- a/core/modules/user/tests/src/Functional/Views/BulkFormTest.php
+++ b/core/modules/user/tests/src/Functional/Views/BulkFormTest.php
@@ -21,6 +21,11 @@ class BulkFormTest extends UserTestBase {
    */
   public static $modules = ['views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/user/tests/src/Functional/Views/FilterPermissionUiTest.php b/core/modules/user/tests/src/Functional/Views/FilterPermissionUiTest.php
index d08c2f31695fa01bb21e8262585a9ca9da4e18a3..18358585835b6c17741766c23f6dafb5ecf672b6 100644
--- a/core/modules/user/tests/src/Functional/Views/FilterPermissionUiTest.php
+++ b/core/modules/user/tests/src/Functional/Views/FilterPermissionUiTest.php
@@ -27,6 +27,11 @@ class FilterPermissionUiTest extends ViewTestBase {
    */
   public static $modules = ['user', 'user_test_views', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/user/tests/src/Functional/Views/HandlerFieldRoleTest.php b/core/modules/user/tests/src/Functional/Views/HandlerFieldRoleTest.php
index 9c2430e11a3cffdb5c0956b71de1c48704780a7d..ca191b5a02777c69c481aa07a79991c8da64f233 100644
--- a/core/modules/user/tests/src/Functional/Views/HandlerFieldRoleTest.php
+++ b/core/modules/user/tests/src/Functional/Views/HandlerFieldRoleTest.php
@@ -20,6 +20,11 @@ class HandlerFieldRoleTest extends UserTestBase {
    */
   public static $testViews = ['test_views_handler_field_role'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testRole() {
     // Create a couple of roles for the view.
     $rolename_a = 'a' . $this->randomMachineName(8);
diff --git a/core/modules/user/tests/src/Functional/Views/HandlerFieldUserNameTest.php b/core/modules/user/tests/src/Functional/Views/HandlerFieldUserNameTest.php
index 0525e3d1fe05b321ba197db79297336fcb597ef6..108121e61d9e1b09dbd0461cd9181806bbb8d827 100644
--- a/core/modules/user/tests/src/Functional/Views/HandlerFieldUserNameTest.php
+++ b/core/modules/user/tests/src/Functional/Views/HandlerFieldUserNameTest.php
@@ -20,6 +20,11 @@ class HandlerFieldUserNameTest extends UserTestBase {
    */
   public static $testViews = ['test_views_handler_field_user_name'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testUserName() {
     /** @var \Drupal\Core\Render\RendererInterface $renderer */
     $renderer = \Drupal::service('renderer');
diff --git a/core/modules/user/tests/src/Functional/Views/HandlerFilterUserNameTest.php b/core/modules/user/tests/src/Functional/Views/HandlerFilterUserNameTest.php
index a5d271092a0213de42a746b7e0372204e99f6bfd..dbb8fc56c43652d456c81d170fbd7afdb8bd2247 100644
--- a/core/modules/user/tests/src/Functional/Views/HandlerFilterUserNameTest.php
+++ b/core/modules/user/tests/src/Functional/Views/HandlerFilterUserNameTest.php
@@ -21,6 +21,11 @@ class HandlerFilterUserNameTest extends ViewTestBase {
    */
   public static $modules = ['views_ui', 'user_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/user/tests/src/Functional/Views/RolesRidArgumentTest.php b/core/modules/user/tests/src/Functional/Views/RolesRidArgumentTest.php
index fd36ec49bd571c7db58c18440a188e1f0643b0f5..50c24f5afb6f9c2fff7599bbac61d7672e60d9a5 100644
--- a/core/modules/user/tests/src/Functional/Views/RolesRidArgumentTest.php
+++ b/core/modules/user/tests/src/Functional/Views/RolesRidArgumentTest.php
@@ -17,6 +17,11 @@ class RolesRidArgumentTest extends UserTestBase {
    */
   public static $testViews = ['test_user_roles_rid'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the generated title of a user: roles argument.
    */
diff --git a/core/modules/user/tests/src/Functional/Views/UserChangedTest.php b/core/modules/user/tests/src/Functional/Views/UserChangedTest.php
index 2271c0ce0726ba5d2c4ac8f0371c9c18c7c9fc7d..d22d2b4710f748f08cc67466f28fe4b80ec81254 100644
--- a/core/modules/user/tests/src/Functional/Views/UserChangedTest.php
+++ b/core/modules/user/tests/src/Functional/Views/UserChangedTest.php
@@ -19,6 +19,11 @@ class UserChangedTest extends ViewTestBase {
    */
   public static $modules = ['views_ui', 'user_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/user/tests/src/Functional/Views/UserFieldsAccessChangeTest.php b/core/modules/user/tests/src/Functional/Views/UserFieldsAccessChangeTest.php
index 7f75cf3aadb9bc51222305efe08f1b1d08b35f42..ca3e8e9cccbb4e08c5158151bf374424f6dc9dd3 100644
--- a/core/modules/user/tests/src/Functional/Views/UserFieldsAccessChangeTest.php
+++ b/core/modules/user/tests/src/Functional/Views/UserFieldsAccessChangeTest.php
@@ -16,6 +16,11 @@ class UserFieldsAccessChangeTest extends UserTestBase {
    */
   public static $modules = ['user_access_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php b/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
index 9f80094c09452650293e643ebae5fcf83b37888c..d62bae8193e660119d34ca8cbe3e3e803ef98e76 100644
--- a/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
+++ b/core/modules/user/tests/src/FunctionalJavascript/RegistrationWithUserFieldsTest.php
@@ -33,6 +33,11 @@ class RegistrationWithUserFieldsTest extends WebDriverTestBase {
    */
   public static $modules = ['field_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/BulkFormTest.php b/core/modules/views/tests/src/Functional/BulkFormTest.php
index 73862992be213847812715e49324b15b1da25665..033902438e74ca35e886ebf17d02c83092d033e4 100644
--- a/core/modules/views/tests/src/Functional/BulkFormTest.php
+++ b/core/modules/views/tests/src/Functional/BulkFormTest.php
@@ -21,6 +21,11 @@ class BulkFormTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'action_bulk_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the bulk form.
    */
diff --git a/core/modules/views/tests/src/Functional/DefaultViewsTest.php b/core/modules/views/tests/src/Functional/DefaultViewsTest.php
index 1e1cbee2a4e9207602a38e3761c8d67dc5e297aa..071786a47072caffeef191175993f71d0c64d6a9 100644
--- a/core/modules/views/tests/src/Functional/DefaultViewsTest.php
+++ b/core/modules/views/tests/src/Functional/DefaultViewsTest.php
@@ -32,6 +32,11 @@ class DefaultViewsTest extends ViewTestBase {
    */
   public static $modules = ['views', 'node', 'search', 'comment', 'taxonomy', 'block', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An array of argument arrays to use for default views.
    *
diff --git a/core/modules/views/tests/src/Functional/Entity/BaseFieldAccessTest.php b/core/modules/views/tests/src/Functional/Entity/BaseFieldAccessTest.php
index 7a75c3cb2fd60c0d7916fc2e7c2aec5ab097c94a..ae81caa8b2fd58b6cd47ec12e7fde746da41bd30 100644
--- a/core/modules/views/tests/src/Functional/Entity/BaseFieldAccessTest.php
+++ b/core/modules/views/tests/src/Functional/Entity/BaseFieldAccessTest.php
@@ -29,6 +29,11 @@ class BaseFieldAccessTest extends ViewTestBase {
     'views', 'views_test_config', 'entity_test', 'node', 'views_entity_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Entity/EntityQueryAccessTest.php b/core/modules/views/tests/src/Functional/Entity/EntityQueryAccessTest.php
index 73a7f655109d5c277a677efa376aa2cdf842dfb4..077e8c30634947bbb4d5627bb12034cbba833573 100644
--- a/core/modules/views/tests/src/Functional/Entity/EntityQueryAccessTest.php
+++ b/core/modules/views/tests/src/Functional/Entity/EntityQueryAccessTest.php
@@ -25,6 +25,11 @@ class EntityQueryAccessTest extends ViewTestBase {
     'views_test_query_access',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that the 'media_access' query tag is respected by Views.
    */
diff --git a/core/modules/views/tests/src/Functional/Entity/FieldEntityTest.php b/core/modules/views/tests/src/Functional/Entity/FieldEntityTest.php
index 2393b6d2699390a035c1ff7d126062d63b00b882..e88c06b277f03a1dfd3f6b6c85bafb0a70471f4e 100644
--- a/core/modules/views/tests/src/Functional/Entity/FieldEntityTest.php
+++ b/core/modules/views/tests/src/Functional/Entity/FieldEntityTest.php
@@ -33,6 +33,11 @@ class FieldEntityTest extends ViewTestBase {
    */
   public static $modules = ['node', 'comment'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Entity/FieldEntityTranslationTest.php b/core/modules/views/tests/src/Functional/Entity/FieldEntityTranslationTest.php
index 2a227c543373b7c04f08e1d6dc9aece9493766d5..6c82768153ee76d4d25f8e21c3ae19369b39b412 100644
--- a/core/modules/views/tests/src/Functional/Entity/FieldEntityTranslationTest.php
+++ b/core/modules/views/tests/src/Functional/Entity/FieldEntityTranslationTest.php
@@ -21,6 +21,11 @@ class FieldEntityTranslationTest extends ViewTestBase {
    */
   public static $modules = ['language', 'locale', 'content_translation', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Entity/FieldRenderedEntityTranslationTest.php b/core/modules/views/tests/src/Functional/Entity/FieldRenderedEntityTranslationTest.php
index 5f04bc9208d7c569120343fb4f19ed6673f66e60..7d7b3d24547d9f2ed862f2244d7f0b7cdafc351d 100644
--- a/core/modules/views/tests/src/Functional/Entity/FieldRenderedEntityTranslationTest.php
+++ b/core/modules/views/tests/src/Functional/Entity/FieldRenderedEntityTranslationTest.php
@@ -18,6 +18,11 @@ class FieldRenderedEntityTranslationTest extends ViewTestBase {
    */
   public static $modules = ['language', 'locale', 'content_translation', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Entity/ViewNonTranslatableEntityTest.php b/core/modules/views/tests/src/Functional/Entity/ViewNonTranslatableEntityTest.php
index 911cd61e66a5c04bfb701824f00372dc1273794b..e8d9094f85a415c3a4b6b6d85ced413ab9f04b64 100644
--- a/core/modules/views/tests/src/Functional/Entity/ViewNonTranslatableEntityTest.php
+++ b/core/modules/views/tests/src/Functional/Entity/ViewNonTranslatableEntityTest.php
@@ -25,6 +25,11 @@ class ViewNonTranslatableEntityTest extends BrowserTestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests displaying a view of non-translatable entities.
    */
diff --git a/core/modules/views/tests/src/Functional/GlossaryTest.php b/core/modules/views/tests/src/Functional/GlossaryTest.php
index ed247f1829bc1de8cb0968d4d6b68a1513053735..04cda6e32b07d3c2ff7b3128fd447608e768a7fb 100644
--- a/core/modules/views/tests/src/Functional/GlossaryTest.php
+++ b/core/modules/views/tests/src/Functional/GlossaryTest.php
@@ -23,6 +23,11 @@ class GlossaryTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the default glossary view.
    */
diff --git a/core/modules/views/tests/src/Functional/Hal/ViewHalJsonAnonTest.php b/core/modules/views/tests/src/Functional/Hal/ViewHalJsonAnonTest.php
index 134b00f223bda62381b327ba39994044dcfcf57b..45e5d3acc0e229f4b87de099cf82967fc3ad888f 100644
--- a/core/modules/views/tests/src/Functional/Hal/ViewHalJsonAnonTest.php
+++ b/core/modules/views/tests/src/Functional/Hal/ViewHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class ViewHalJsonAnonTest extends ViewResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Hal/ViewHalJsonBasicAuthTest.php b/core/modules/views/tests/src/Functional/Hal/ViewHalJsonBasicAuthTest.php
index 87c39852cff537138a3be311673a84575fe9623f..9bedfb5135659e01d3703d9f38ef3b03e8c584db 100644
--- a/core/modules/views/tests/src/Functional/Hal/ViewHalJsonBasicAuthTest.php
+++ b/core/modules/views/tests/src/Functional/Hal/ViewHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class ViewHalJsonBasicAuthTest extends ViewResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Hal/ViewHalJsonCookieTest.php b/core/modules/views/tests/src/Functional/Hal/ViewHalJsonCookieTest.php
index aa5aa4f6b7ad71794212f2a64b95ece915297435..da2ca72b7b794c84505f10073948da62e03f4e3f 100644
--- a/core/modules/views/tests/src/Functional/Hal/ViewHalJsonCookieTest.php
+++ b/core/modules/views/tests/src/Functional/Hal/ViewHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class ViewHalJsonCookieTest extends ViewResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Handler/AreaHTTPStatusCodeTest.php b/core/modules/views/tests/src/Functional/Handler/AreaHTTPStatusCodeTest.php
index dc914ce219e6d0f8aeb575b647faf5e366d2771c..d284f4719a061697ac86dc3c583e9db3ba1374a1 100644
--- a/core/modules/views/tests/src/Functional/Handler/AreaHTTPStatusCodeTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/AreaHTTPStatusCodeTest.php
@@ -27,6 +27,11 @@ class AreaHTTPStatusCodeTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the area handler.
    */
diff --git a/core/modules/views/tests/src/Functional/Handler/AreaTest.php b/core/modules/views/tests/src/Functional/Handler/AreaTest.php
index 1827319bbd05d48a6181cd788ed8d143d09d33d4..170147eab00b7ef1fb33ff5eccf46b62db25a461 100644
--- a/core/modules/views/tests/src/Functional/Handler/AreaTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/AreaTest.php
@@ -29,6 +29,11 @@ class AreaTest extends ViewTestBase {
    */
   public static $modules = ['node', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Handler/AreaTitleWebTest.php b/core/modules/views/tests/src/Functional/Handler/AreaTitleWebTest.php
index 9e1fcfad233dc7c1a71e4f32953600f390b536d0..23ab8dc28ade973f812a945eb9d68ba1745c7014 100644
--- a/core/modules/views/tests/src/Functional/Handler/AreaTitleWebTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/AreaTitleWebTest.php
@@ -20,6 +20,11 @@ class AreaTitleWebTest extends ViewTestBase {
    */
   public static $testViews = ['test_area_title'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Handler/FieldDropButtonTest.php b/core/modules/views/tests/src/Functional/Handler/FieldDropButtonTest.php
index e0e380b0f8d68eefec6387705643a75f68a92474..7eae8284a671bb25bcac0ea4beb6cb45bcd1b1e9 100644
--- a/core/modules/views/tests/src/Functional/Handler/FieldDropButtonTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FieldDropButtonTest.php
@@ -26,6 +26,11 @@ class FieldDropButtonTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Handler/FieldEntityLinkBaseTest.php b/core/modules/views/tests/src/Functional/Handler/FieldEntityLinkBaseTest.php
index bd3f3f65cf7138f0d2429c76799cf2859483dca0..04794ecd9779b1c26b2288dd61ce336310d14635 100644
--- a/core/modules/views/tests/src/Functional/Handler/FieldEntityLinkBaseTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FieldEntityLinkBaseTest.php
@@ -25,6 +25,11 @@ class FieldEntityLinkBaseTest extends ViewTestBase {
    */
   public static $modules = ['node', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Handler/FieldEntityOperationsTest.php b/core/modules/views/tests/src/Functional/Handler/FieldEntityOperationsTest.php
index c8f962dbe8ef772b5022bc3521a919850324afa0..c6c5a0909df99f73aa795647849dc51f11cf9fbc 100644
--- a/core/modules/views/tests/src/Functional/Handler/FieldEntityOperationsTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FieldEntityOperationsTest.php
@@ -28,6 +28,11 @@ class FieldEntityOperationsTest extends ViewTestBase {
    */
   public static $modules = ['node', 'language', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Handler/FieldGroupRowsWebTest.php b/core/modules/views/tests/src/Functional/Handler/FieldGroupRowsWebTest.php
index 275960cb0d4a9162cd43c890eff0e019cea9a2f1..aa4a5617b7990877eb253500bf1c24fb80534260 100644
--- a/core/modules/views/tests/src/Functional/Handler/FieldGroupRowsWebTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FieldGroupRowsWebTest.php
@@ -28,6 +28,11 @@ class FieldGroupRowsWebTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The page node type.
    *
diff --git a/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php b/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php
index c4715ab61c6d8a787e94fa057bfd12fb1a0693e1..7b3e747a555d0ca59b44d0fb81a6752e5d380347 100644
--- a/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php
@@ -33,6 +33,11 @@ class FieldWebTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Maps between the key in the expected result and the query result.
    *
diff --git a/core/modules/views/tests/src/Functional/Handler/FilterDateTest.php b/core/modules/views/tests/src/Functional/Handler/FilterDateTest.php
index 90bddc5f7a7de195219054f4f01d90a9db06a6ab..0ef10459b60f6ca3c5aeb44f19673e43400e3989 100644
--- a/core/modules/views/tests/src/Functional/Handler/FilterDateTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FilterDateTest.php
@@ -31,6 +31,11 @@ class FilterDateTest extends ViewTestBase {
    */
   public static $modules = ['node', 'views_ui', 'datetime'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * The date formatter.
    *
diff --git a/core/modules/views/tests/src/Functional/Handler/FilterPlaceholderTextTest.php b/core/modules/views/tests/src/Functional/Handler/FilterPlaceholderTextTest.php
index 7d852f7c87003378789354c130ed09dde7e84bff..4453acbac47a33a29ab1afefba1799b652c8baeb 100644
--- a/core/modules/views/tests/src/Functional/Handler/FilterPlaceholderTextTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FilterPlaceholderTextTest.php
@@ -23,6 +23,11 @@ class FilterPlaceholderTextTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that HTML placeholders are added, when appropriate.
    */
diff --git a/core/modules/views/tests/src/Functional/Handler/HandlerAllTest.php b/core/modules/views/tests/src/Functional/Handler/HandlerAllTest.php
index e08f01d67543688a9724ff908aa932ad7ee1ac5a..e948273ec0b13c7d11a985253c7d47a0e1dec8ef 100644
--- a/core/modules/views/tests/src/Functional/Handler/HandlerAllTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/HandlerAllTest.php
@@ -44,6 +44,11 @@ class HandlerAllTest extends ViewTestBase {
     'user',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests most of the handlers.
    */
diff --git a/core/modules/views/tests/src/Functional/Handler/HandlerTest.php b/core/modules/views/tests/src/Functional/Handler/HandlerTest.php
index cffe6d1402628934691481f415d11f0dd77c65b8..08ee8f7cbf2e92cb461a33ebb566f36eda739a9a 100644
--- a/core/modules/views/tests/src/Functional/Handler/HandlerTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/HandlerTest.php
@@ -32,6 +32,11 @@ class HandlerTest extends ViewTestBase {
    */
   public static $modules = ['views_ui', 'comment', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
     $this->drupalCreateContentType(['type' => 'page']);
diff --git a/core/modules/views/tests/src/Functional/Plugin/AccessTest.php b/core/modules/views/tests/src/Functional/Plugin/AccessTest.php
index 31a64cc1cf108d0b182c93d88b2f60771ada624c..317d6da374563f9da56cdfb22d49b58231f155dc 100644
--- a/core/modules/views/tests/src/Functional/Plugin/AccessTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/AccessTest.php
@@ -29,6 +29,11 @@ class AccessTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Web user for testing.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/ArgumentDefaultTest.php b/core/modules/views/tests/src/Functional/Plugin/ArgumentDefaultTest.php
index a5eb2f02fe199b918e8d40b29c98a53b52d6cf2f..fe6ff11510f34f094daf296aeb8a2a926934e48a 100644
--- a/core/modules/views/tests/src/Functional/Plugin/ArgumentDefaultTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/ArgumentDefaultTest.php
@@ -31,6 +31,11 @@ class ArgumentDefaultTest extends ViewTestBase {
     'test_argument_default_query_param',
     ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/CacheTagTest.php b/core/modules/views/tests/src/Functional/Plugin/CacheTagTest.php
index 32081addb25edd9f31906751723db99503d34baf..1adba7d801bf9044a6532ca5794b02a02a62e932 100644
--- a/core/modules/views/tests/src/Functional/Plugin/CacheTagTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/CacheTagTest.php
@@ -29,6 +29,11 @@ class CacheTagTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The node storage.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/CacheWebTest.php b/core/modules/views/tests/src/Functional/Plugin/CacheWebTest.php
index c919bcb8312fdb6693739b0b07071020b3408298..016c0abd8c3c63c0aaecfe08e2f5faae85b9186d 100644
--- a/core/modules/views/tests/src/Functional/Plugin/CacheWebTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/CacheWebTest.php
@@ -31,6 +31,11 @@ class CacheWebTest extends ViewTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Plugin/ContextualFiltersBlockContextTest.php b/core/modules/views/tests/src/Functional/Plugin/ContextualFiltersBlockContextTest.php
index 9db8d155f63035a5e53aaecec2032fdb77eecc91..2dc22f75482e58a721fc90803a8b59eb81e833a3 100644
--- a/core/modules/views/tests/src/Functional/Plugin/ContextualFiltersBlockContextTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/ContextualFiltersBlockContextTest.php
@@ -23,6 +23,11 @@ class ContextualFiltersBlockContextTest extends ViewTestBase {
    */
   public static $modules = ['block', 'block_test_views', 'views_ui', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/DisabledDisplayTest.php b/core/modules/views/tests/src/Functional/Plugin/DisabledDisplayTest.php
index a85612cca2825f4b9534333935ae0a4998fe44f9..4fe00c745869c0298f44ba87f15cac24d02aa673 100644
--- a/core/modules/views/tests/src/Functional/Plugin/DisabledDisplayTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/DisabledDisplayTest.php
@@ -26,6 +26,11 @@ class DisabledDisplayTest extends ViewTestBase {
    */
   public static $modules = ['block', 'node', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Plugin/DisplayAttachmentTest.php b/core/modules/views/tests/src/Functional/Plugin/DisplayAttachmentTest.php
index 44668447c783c16347e4e169d0bb55b28159b6b5..a09faf12b9cc22ed3d67385a6def6648495ba7a0 100644
--- a/core/modules/views/tests/src/Functional/Plugin/DisplayAttachmentTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/DisplayAttachmentTest.php
@@ -27,6 +27,11 @@ class DisplayAttachmentTest extends ViewTestBase {
    */
   public static $modules = ['node', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Plugin/DisplayEntityReferenceTest.php b/core/modules/views/tests/src/Functional/Plugin/DisplayEntityReferenceTest.php
index 817c51d7875adf8e0b3bab69f0a2cfcad1c5a28d..8a9b32db121e872240d1aff4f21ad372e18d75b1 100644
--- a/core/modules/views/tests/src/Functional/Plugin/DisplayEntityReferenceTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/DisplayEntityReferenceTest.php
@@ -34,6 +34,11 @@ class DisplayEntityReferenceTest extends ViewTestBase {
    */
   public static $modules = ['entity_test', 'field', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The used field name in the test.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/DisplayFeedTest.php b/core/modules/views/tests/src/Functional/Plugin/DisplayFeedTest.php
index b4afccd478ba4030dced217f958a4fa70c698c18..456450f80738188c31dd0f4060d258e4730b3886 100644
--- a/core/modules/views/tests/src/Functional/Plugin/DisplayFeedTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/DisplayFeedTest.php
@@ -28,6 +28,11 @@ class DisplayFeedTest extends ViewTestBase {
    */
   public static $modules = ['block', 'node', 'views', 'views_test_rss'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Plugin/DisplayPageWebTest.php b/core/modules/views/tests/src/Functional/Plugin/DisplayPageWebTest.php
index 501d9226eedab7977c5dd5cb9dd24a6164e46742..d361db0e4b1273feffabe34e267fd7dde0b19a2b 100644
--- a/core/modules/views/tests/src/Functional/Plugin/DisplayPageWebTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/DisplayPageWebTest.php
@@ -29,6 +29,11 @@ class DisplayPageWebTest extends ViewTestBase {
    */
   public static $modules = ['menu_ui', 'block', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Plugin/DisplayTest.php b/core/modules/views/tests/src/Functional/Plugin/DisplayTest.php
index 44905a3926530ce35d6c254beba5275d2a4d23a2..1b2adc228cf78722bd295f8ac4b265bacaed22e4 100644
--- a/core/modules/views/tests/src/Functional/Plugin/DisplayTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/DisplayTest.php
@@ -28,6 +28,11 @@ class DisplayTest extends ViewTestBase {
    */
   public static $modules = ['views_ui', 'node', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp();
 
diff --git a/core/modules/views/tests/src/Functional/Plugin/ExposedFormCheckboxesTest.php b/core/modules/views/tests/src/Functional/Plugin/ExposedFormCheckboxesTest.php
index cecc8fabd2a87d8cf3b1da9cc8142f4bbf443816..f6bd8adae37579e65639f2abd8228af622925add 100644
--- a/core/modules/views/tests/src/Functional/Plugin/ExposedFormCheckboxesTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/ExposedFormCheckboxesTest.php
@@ -29,6 +29,11 @@ class ExposedFormCheckboxesTest extends ViewTestBase {
    */
   public static $modules = ['node', 'views_ui', 'taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test terms.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php b/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php
index 53a0e4dda7e3d7b978a09f1913ee6749f593398d..6240fb041212d5fa0e618b5150b41c8d05c40de0 100644
--- a/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php
@@ -33,6 +33,11 @@ class ExposedFormTest extends ViewTestBase {
    */
   public static $modules = ['node', 'views_ui', 'block', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Plugin/FilterTest.php b/core/modules/views/tests/src/Functional/Plugin/FilterTest.php
index 90c00f786dd42840c500b2695eaa084b2c4e85c0..d968125deaef1d955684c9e929bc19bf50fd08b3 100644
--- a/core/modules/views/tests/src/Functional/Plugin/FilterTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/FilterTest.php
@@ -29,6 +29,11 @@ class FilterTest extends ViewTestBase {
    */
   public static $modules = ['views_ui', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Plugin/MenuLinkTest.php b/core/modules/views/tests/src/Functional/Plugin/MenuLinkTest.php
index 77591b44dde104553ae1dffd1346dda7114b7e16..1bba00e1ba8a9ea557a70373a5da9ee2bdf7ddef 100644
--- a/core/modules/views/tests/src/Functional/Plugin/MenuLinkTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/MenuLinkTest.php
@@ -26,6 +26,11 @@ class MenuLinkTest extends ViewTestBase {
    */
   public static $modules = ['views', 'views_ui', 'user', 'node', 'menu_ui', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to administer views, menus and view content.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/MiniPagerTest.php b/core/modules/views/tests/src/Functional/Plugin/MiniPagerTest.php
index 492d22f987979695678bd7e5e07db9bb2ab06a1e..5ab9390f2e78986d810a6885e3da6a3a77ac00ec 100644
--- a/core/modules/views/tests/src/Functional/Plugin/MiniPagerTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/MiniPagerTest.php
@@ -27,6 +27,11 @@ class MiniPagerTest extends ViewTestBase {
    */
   public static $modules = ['node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Nodes used by the test.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/NumericFormatPluralTest.php b/core/modules/views/tests/src/Functional/Plugin/NumericFormatPluralTest.php
index c20fa6e5c6b93fb9e50aae8e61f8cb0f645e9203..57a2f8befe42109a235a8566bb481e2aff391cc6 100644
--- a/core/modules/views/tests/src/Functional/Plugin/NumericFormatPluralTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/NumericFormatPluralTest.php
@@ -21,6 +21,11 @@ class NumericFormatPluralTest extends ViewTestBase {
    */
   public static $modules = ['views_ui', 'file', 'language', 'locale'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/PagerTest.php b/core/modules/views/tests/src/Functional/Plugin/PagerTest.php
index 56c37fb3576896f97a4d29b7ad3f30667b70777a..c7c68674010255eaf0b817cf3dc2bf33f27c2a77 100644
--- a/core/modules/views/tests/src/Functional/Plugin/PagerTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/PagerTest.php
@@ -30,6 +30,11 @@ class PagerTest extends ViewTestBase {
    */
   public static $modules = ['node', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * String translation storage object.
    *
diff --git a/core/modules/views/tests/src/Functional/Plugin/StyleOpmlTest.php b/core/modules/views/tests/src/Functional/Plugin/StyleOpmlTest.php
index 90f027c7f50a466b61aadf9cf593c0d13d4126df..88fc6b59023b031c4c09ec203ac2477d3e1b5eb8 100644
--- a/core/modules/views/tests/src/Functional/Plugin/StyleOpmlTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/StyleOpmlTest.php
@@ -26,6 +26,11 @@ class StyleOpmlTest extends ViewTestBase {
    */
   public static $modules = ['aggregator'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Plugin/StyleSummaryTest.php b/core/modules/views/tests/src/Functional/Plugin/StyleSummaryTest.php
index a2359b97344e974d19e63a5dc2b114727687df5c..f39f6b43ac8ca2413f8d440cd252d1a04094edb4 100644
--- a/core/modules/views/tests/src/Functional/Plugin/StyleSummaryTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/StyleSummaryTest.php
@@ -17,6 +17,11 @@ class StyleSummaryTest extends ViewTestBase {
    */
   public static $modules = ['entity_test', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Plugin/StyleTableTest.php b/core/modules/views/tests/src/Functional/Plugin/StyleTableTest.php
index cbfd0288d4f53a975b6c0ea5d3a0064ec075f38e..3af722395d48e860a814e5dabc5de49c382ff077 100644
--- a/core/modules/views/tests/src/Functional/Plugin/StyleTableTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/StyleTableTest.php
@@ -21,6 +21,11 @@ class StyleTableTest extends ViewTestBase {
    */
   public static $testViews = ['test_table'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Plugin/ViewsBulkTest.php b/core/modules/views/tests/src/Functional/Plugin/ViewsBulkTest.php
index e3faa88405fd8cbb5fa8eb017b9b56f9658873ba..03a06428a0f2ea511bf9e076ab1a84e4e409d834 100644
--- a/core/modules/views/tests/src/Functional/Plugin/ViewsBulkTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/ViewsBulkTest.php
@@ -25,6 +25,11 @@ class ViewsBulkTest extends ViewTestBase {
    */
   public static $modules = ['node', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Plugin/ViewsFormTest.php b/core/modules/views/tests/src/Functional/Plugin/ViewsFormTest.php
index 67c4cb035b78d3f14f1ecdc2e9559889e23f7ca9..d8556ca1bc9b9d96433fde22ce5ef5142b659da0 100644
--- a/core/modules/views/tests/src/Functional/Plugin/ViewsFormTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/ViewsFormTest.php
@@ -18,6 +18,11 @@ class ViewsFormTest extends ViewTestBase {
    */
   public static $modules = ['action_bulk_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the Views form wrapper.
    */
diff --git a/core/modules/views/tests/src/Functional/RenderCacheWebTest.php b/core/modules/views/tests/src/Functional/RenderCacheWebTest.php
index f8dfdd810da26b8abd7532f6a0161b07cf75f0e6..57e63999149f5c1a65a46c209f25bcb42f4db1ae 100644
--- a/core/modules/views/tests/src/Functional/RenderCacheWebTest.php
+++ b/core/modules/views/tests/src/Functional/RenderCacheWebTest.php
@@ -16,6 +16,11 @@ class RenderCacheWebTest extends ViewTestBase {
    */
   public static $modules = ['node', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Rest/ViewJsonAnonTest.php b/core/modules/views/tests/src/Functional/Rest/ViewJsonAnonTest.php
index 694aee165bc107316be2c943a346f3fdbc47d284..e7e7f76f6fdfba9f596a111969195cf241a5442e 100644
--- a/core/modules/views/tests/src/Functional/Rest/ViewJsonAnonTest.php
+++ b/core/modules/views/tests/src/Functional/Rest/ViewJsonAnonTest.php
@@ -21,4 +21,9 @@ class ViewJsonAnonTest extends ViewResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/views/tests/src/Functional/Rest/ViewJsonBasicAuthTest.php b/core/modules/views/tests/src/Functional/Rest/ViewJsonBasicAuthTest.php
index 4ebe08c3367cc5a7dbe99c1f21f46f58c5493463..c6078203dad972e62ee8dadd5efd199c6436b201 100644
--- a/core/modules/views/tests/src/Functional/Rest/ViewJsonBasicAuthTest.php
+++ b/core/modules/views/tests/src/Functional/Rest/ViewJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class ViewJsonBasicAuthTest extends ViewResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Rest/ViewJsonCookieTest.php b/core/modules/views/tests/src/Functional/Rest/ViewJsonCookieTest.php
index feeeab260277874b1c304c502ba86d98c9d8cde6..e772c4bbcb50f9f6e9a0ad999f9591bde6066e72 100644
--- a/core/modules/views/tests/src/Functional/Rest/ViewJsonCookieTest.php
+++ b/core/modules/views/tests/src/Functional/Rest/ViewJsonCookieTest.php
@@ -26,4 +26,9 @@ class ViewJsonCookieTest extends ViewResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/views/tests/src/Functional/Rest/ViewXmlAnonTest.php b/core/modules/views/tests/src/Functional/Rest/ViewXmlAnonTest.php
index 7582a54f056f585e2a981082324824106bbfc75b..ad94fec6d9baae8dafc2cbfa8600fcd2f3d38c97 100644
--- a/core/modules/views/tests/src/Functional/Rest/ViewXmlAnonTest.php
+++ b/core/modules/views/tests/src/Functional/Rest/ViewXmlAnonTest.php
@@ -23,4 +23,9 @@ class ViewXmlAnonTest extends ViewResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/views/tests/src/Functional/Rest/ViewXmlBasicAuthTest.php b/core/modules/views/tests/src/Functional/Rest/ViewXmlBasicAuthTest.php
index ba9e58b3e6b1c56e010ca124b3348eaa7b2d481a..52ab59f0b11e4c97e9114bedc671987509ea1647 100644
--- a/core/modules/views/tests/src/Functional/Rest/ViewXmlBasicAuthTest.php
+++ b/core/modules/views/tests/src/Functional/Rest/ViewXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class ViewXmlBasicAuthTest extends ViewResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/Rest/ViewXmlCookieTest.php b/core/modules/views/tests/src/Functional/Rest/ViewXmlCookieTest.php
index 8f362a06c140f83cf15aa39a38d6755ae6878c80..4f5e9169b31ce680d2811fd035b05f9b229cc918 100644
--- a/core/modules/views/tests/src/Functional/Rest/ViewXmlCookieTest.php
+++ b/core/modules/views/tests/src/Functional/Rest/ViewXmlCookieTest.php
@@ -28,4 +28,9 @@ class ViewXmlCookieTest extends ViewResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/views/tests/src/Functional/SearchIntegrationTest.php b/core/modules/views/tests/src/Functional/SearchIntegrationTest.php
index fbbc96582b72efa6fa4d0758f3b210c70d26784b..134417329d1b87bf1521d4239d3681fa2abcb48c 100644
--- a/core/modules/views/tests/src/Functional/SearchIntegrationTest.php
+++ b/core/modules/views/tests/src/Functional/SearchIntegrationTest.php
@@ -21,6 +21,11 @@ class SearchIntegrationTest extends ViewTestBase {
    */
   public static $modules = ['node', 'search'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views/tests/src/Functional/SearchMultilingualTest.php b/core/modules/views/tests/src/Functional/SearchMultilingualTest.php
index e7763e5362c56d8a290baf8dedfebae39336b271..78a6c3f2c617142b13e108ec1aca0fa835e6bede 100644
--- a/core/modules/views/tests/src/Functional/SearchMultilingualTest.php
+++ b/core/modules/views/tests/src/Functional/SearchMultilingualTest.php
@@ -22,6 +22,11 @@ class SearchMultilingualTest extends ViewTestBase {
    */
   public static $modules = ['node', 'search', 'language', 'content_translation'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views/tests/src/Functional/TaxonomyGlossaryTest.php b/core/modules/views/tests/src/Functional/TaxonomyGlossaryTest.php
index 6e9d477677b09e1695e5f9ad9a961c6c774fbf5b..65f8e02366927eb09aea458b8fd28212c1536c9f 100644
--- a/core/modules/views/tests/src/Functional/TaxonomyGlossaryTest.php
+++ b/core/modules/views/tests/src/Functional/TaxonomyGlossaryTest.php
@@ -20,6 +20,11 @@ class TaxonomyGlossaryTest extends ViewTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views/tests/src/Functional/UserBatchActionTest.php b/core/modules/views/tests/src/Functional/UserBatchActionTest.php
index 60c1d255876cbd563bc7be30bc499d568fd723a0..efb78079ae7e353cb1b34d255da1b04c6387ed36 100644
--- a/core/modules/views/tests/src/Functional/UserBatchActionTest.php
+++ b/core/modules/views/tests/src/Functional/UserBatchActionTest.php
@@ -19,6 +19,11 @@ class UserBatchActionTest extends BrowserTestBase {
    */
   public static $modules = ['user', 'user_batch_action_test', 'views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests user admin batch.
    */
diff --git a/core/modules/views/tests/src/Functional/UserPathTest.php b/core/modules/views/tests/src/Functional/UserPathTest.php
index 27a0f27a9bbaa500bf4c9e6528e632fc4bef7ed4..d31452bdae448dab6dfe41e731e93ebe5235962d 100644
--- a/core/modules/views/tests/src/Functional/UserPathTest.php
+++ b/core/modules/views/tests/src/Functional/UserPathTest.php
@@ -14,6 +14,11 @@ class UserPathTest extends ViewTestBase {
    */
   public static $modules = ['views', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The test views to use.
    *
diff --git a/core/modules/views/tests/src/Functional/ViewAjaxTest.php b/core/modules/views/tests/src/Functional/ViewAjaxTest.php
index 9f8c6022181c30a4eb5d664085251c08f2d83fa4..32236d8f55c790b161b6274a016e1ee1daac5e2b 100644
--- a/core/modules/views/tests/src/Functional/ViewAjaxTest.php
+++ b/core/modules/views/tests/src/Functional/ViewAjaxTest.php
@@ -18,6 +18,11 @@ class ViewAjaxTest extends ViewTestBase {
    */
   public static $testViews = ['test_ajax_view', 'test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/ViewElementTest.php b/core/modules/views/tests/src/Functional/ViewElementTest.php
index 2dbc54f6b50570f5926f2233d8dd281faaa73cd5..b682df7604bd84e83687cac3cbcc3d54f0154ee3 100644
--- a/core/modules/views/tests/src/Functional/ViewElementTest.php
+++ b/core/modules/views/tests/src/Functional/ViewElementTest.php
@@ -18,6 +18,11 @@ class ViewElementTest extends ViewTestBase {
    */
   public static $testViews = ['test_view_embed'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/ViewsEscapingTest.php b/core/modules/views/tests/src/Functional/ViewsEscapingTest.php
index d66d90863c52be96cb6485a481f94c199a3df728..c10ff8144b181df5f28e42e0c99b72d35abf3650 100644
--- a/core/modules/views/tests/src/Functional/ViewsEscapingTest.php
+++ b/core/modules/views/tests/src/Functional/ViewsEscapingTest.php
@@ -16,6 +16,11 @@ class ViewsEscapingTest extends ViewTestBase {
    */
   public static $testViews = ['test_page_display', 'test_field_header'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Used by WebTestBase::setup()
    *
diff --git a/core/modules/views/tests/src/Functional/ViewsFormMultipleTest.php b/core/modules/views/tests/src/Functional/ViewsFormMultipleTest.php
index c4c709e3bfc6e14c3827ac58319e86da0230c27e..5d420cf04de5888a40051dab5e04574428ed1cf0 100644
--- a/core/modules/views/tests/src/Functional/ViewsFormMultipleTest.php
+++ b/core/modules/views/tests/src/Functional/ViewsFormMultipleTest.php
@@ -16,6 +16,11 @@ class ViewsFormMultipleTest extends ViewTestBase {
    */
   public static $testViews = ['test_form_multiple'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/ViewsNoResultsBehaviorTest.php b/core/modules/views/tests/src/Functional/ViewsNoResultsBehaviorTest.php
index bb8a77eca29a7caa623ac3d1ce21dcee7c6b4afc..be15beb8ce8e5787874e64449781229cd082327e 100644
--- a/core/modules/views/tests/src/Functional/ViewsNoResultsBehaviorTest.php
+++ b/core/modules/views/tests/src/Functional/ViewsNoResultsBehaviorTest.php
@@ -16,6 +16,11 @@ class ViewsNoResultsBehaviorTest extends ViewTestBase {
    */
   public static $modules = ['node', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/Functional/ViewsThemeIntegrationTest.php b/core/modules/views/tests/src/Functional/ViewsThemeIntegrationTest.php
index 5807dad53518c20642fa5082ff1eef1a92daf251..3dcfa00b41fa747b0532fe5474460dc90553f0b3 100644
--- a/core/modules/views/tests/src/Functional/ViewsThemeIntegrationTest.php
+++ b/core/modules/views/tests/src/Functional/ViewsThemeIntegrationTest.php
@@ -18,6 +18,11 @@ class ViewsThemeIntegrationTest extends ViewTestBase {
    */
   public static $testViews = ['test_page_display'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 
   /**
    * Used by WebTestBase::setup()
diff --git a/core/modules/views/tests/src/Functional/Wizard/BasicTest.php b/core/modules/views/tests/src/Functional/Wizard/BasicTest.php
index 8b92beba1a66b55978067fa5e3e41ae75b27f374..79cf695fedcdeb64e16d44d4616c320890c88658 100644
--- a/core/modules/views/tests/src/Functional/Wizard/BasicTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/BasicTest.php
@@ -14,6 +14,11 @@
  */
 class BasicTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Wizard/EntityTestRevisionTest.php b/core/modules/views/tests/src/Functional/Wizard/EntityTestRevisionTest.php
index 2c5f52fcae312c03850158f2903f979c5e38549c..2e59b61dbd27a19f7b2e6754ec91206a805f3b08 100644
--- a/core/modules/views/tests/src/Functional/Wizard/EntityTestRevisionTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/EntityTestRevisionTest.php
@@ -14,6 +14,11 @@ class EntityTestRevisionTest extends WizardTestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests creating a view of revisions where the type is not on the base table.
    */
diff --git a/core/modules/views/tests/src/Functional/Wizard/ItemsPerPageTest.php b/core/modules/views/tests/src/Functional/Wizard/ItemsPerPageTest.php
index b42baf5cd06367843cf4c6c9403c8a9783ec0416..4ab72da1df27bab26a5b63ae0a6f82c43d74c146 100644
--- a/core/modules/views/tests/src/Functional/Wizard/ItemsPerPageTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/ItemsPerPageTest.php
@@ -10,6 +10,11 @@
  */
 class ItemsPerPageTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Wizard/MenuTest.php b/core/modules/views/tests/src/Functional/Wizard/MenuTest.php
index eb106f60e1f48be3d83f340101d49f2d57085d6f..98f7d619df4e0c2b19939d9ecd9e2f3fca057d76 100644
--- a/core/modules/views/tests/src/Functional/Wizard/MenuTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/MenuTest.php
@@ -12,6 +12,11 @@
  */
 class MenuTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the menu functionality.
    */
diff --git a/core/modules/views/tests/src/Functional/Wizard/NodeWizardTest.php b/core/modules/views/tests/src/Functional/Wizard/NodeWizardTest.php
index 21bdf1709da66e6c62cb523577e07b0ee4e847e3..6f245462313322148f12ec0126739b96aba82eb1 100644
--- a/core/modules/views/tests/src/Functional/Wizard/NodeWizardTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/NodeWizardTest.php
@@ -10,6 +10,11 @@
  */
 class NodeWizardTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests creating a view with node titles.
    */
diff --git a/core/modules/views/tests/src/Functional/Wizard/PagerTest.php b/core/modules/views/tests/src/Functional/Wizard/PagerTest.php
index c8c697c08145911388b8a54f4b7fa5f5b663f494..92bc0035ed0efa0e094799a541d90d7ac7f08503 100644
--- a/core/modules/views/tests/src/Functional/Wizard/PagerTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/PagerTest.php
@@ -9,6 +9,11 @@
  */
 class PagerTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the pager option.
    */
diff --git a/core/modules/views/tests/src/Functional/Wizard/SortingTest.php b/core/modules/views/tests/src/Functional/Wizard/SortingTest.php
index ee36bf2f7ad7def28c8b7ac488d7ee6d4f7ef654..af8b0a12c93909dae5821482a743a466cfe0eada 100644
--- a/core/modules/views/tests/src/Functional/Wizard/SortingTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/SortingTest.php
@@ -9,6 +9,11 @@
  */
 class SortingTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views/tests/src/Functional/Wizard/TaggedWithTest.php b/core/modules/views/tests/src/Functional/Wizard/TaggedWithTest.php
index 0a8d67424877d62beae9610d0bfc23f2f1028643..4eee68c7607aa0aedaf665064844c15f8f4a08b4 100644
--- a/core/modules/views/tests/src/Functional/Wizard/TaggedWithTest.php
+++ b/core/modules/views/tests/src/Functional/Wizard/TaggedWithTest.php
@@ -23,6 +23,11 @@ class TaggedWithTest extends WizardTestBase {
    */
   public static $modules = ['taxonomy'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Node type with an autocomplete tagging field.
    *
diff --git a/core/modules/views/tests/src/FunctionalJavascript/BlockExposedFilterAJAXTest.php b/core/modules/views/tests/src/FunctionalJavascript/BlockExposedFilterAJAXTest.php
index c483ba0331a2d942af511edc4924ab64d8e688ee..e2000b3f9733f7b4b38b5316e5922fb80f23365a 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/BlockExposedFilterAJAXTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/BlockExposedFilterAJAXTest.php
@@ -24,6 +24,11 @@ class BlockExposedFilterAJAXTest extends WebDriverTestBase {
 
   public static $testViews = ['test_block_exposed_ajax', 'test_block_exposed_ajax_with_page'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/FunctionalJavascript/ClickSortingAJAXTest.php b/core/modules/views/tests/src/FunctionalJavascript/ClickSortingAJAXTest.php
index c45255e543b63b7c995fb5b27d5fa5e0411fdbe5..19c48a7093c2216279c29eb732a2d2a748ca2beb 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/ClickSortingAJAXTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/ClickSortingAJAXTest.php
@@ -22,6 +22,11 @@ class ClickSortingAJAXTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_test_config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public static $testViews = ['test_content_ajax'];
 
   /**
diff --git a/core/modules/views/tests/src/FunctionalJavascript/ExposedFilterAJAXTest.php b/core/modules/views/tests/src/FunctionalJavascript/ExposedFilterAJAXTest.php
index 0ab4277c3140a98a13fd09f7dbca790195346422..0fa130156bb6e3deac339411d8eda806a1821d7c 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/ExposedFilterAJAXTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/ExposedFilterAJAXTest.php
@@ -21,6 +21,11 @@ class ExposedFilterAJAXTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_test_modal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views/tests/src/FunctionalJavascript/GlossaryViewTest.php b/core/modules/views/tests/src/FunctionalJavascript/GlossaryViewTest.php
index 8da67861ad6dbb87f13c65ed6f5835706c1fc8db..aff18ad345346d9e859968d55ff73069841c6707 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/GlossaryViewTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/GlossaryViewTest.php
@@ -24,6 +24,11 @@ class GlossaryViewTest extends WebDriverTestBase {
    */
   public static $modules = ['language', 'node', 'views', 'views_test_config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * @var array
    * The test Views to enable.
diff --git a/core/modules/views/tests/src/FunctionalJavascript/PaginationAJAXTest.php b/core/modules/views/tests/src/FunctionalJavascript/PaginationAJAXTest.php
index 8febc85c5f78e518e2d3a1875723e5a6e89f5568..84f6936968e1e5bb76fb0c1e4227d86f80d64f53 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/PaginationAJAXTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/PaginationAJAXTest.php
@@ -22,6 +22,11 @@ class PaginationAJAXTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_test_config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * @var array
    * Test Views to enable.
diff --git a/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/ContextualFilterTest.php b/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/ContextualFilterTest.php
index f0ac6085487c076ee1d5e45ff7f08a1b5a928678..baf00034ed5940d8ae763dd07efbf38eeb982a33 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/ContextualFilterTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/ContextualFilterTest.php
@@ -17,6 +17,11 @@ class ContextualFilterTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui', 'views_test_config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/FieldTest.php b/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/FieldTest.php
index 079fe99ee4af000269e8016acb21f2a5aef92d78..b28ba577b6e0cc6d91937bcf0b7ed6ccd32d40df 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/FieldTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/FieldTest.php
@@ -21,6 +21,11 @@ class FieldTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui', 'views_test_config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/GroupedExposedFilterTest.php b/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/GroupedExposedFilterTest.php
index 1bc8a486d32e4ddd77acb5cb2bc5d8c4a7e6052f..e61e8eaff3687cd6bac6d2a2749172746219afa8 100644
--- a/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/GroupedExposedFilterTest.php
+++ b/core/modules/views/tests/src/FunctionalJavascript/Plugin/views/Handler/GroupedExposedFilterTest.php
@@ -19,6 +19,11 @@ class GroupedExposedFilterTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui', 'user', 'views_test_config'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/AnalyzeTest.php b/core/modules/views_ui/tests/src/Functional/AnalyzeTest.php
index 2492944235cb2db1c7efc9ef0ee5865cac3ae264..ac2a8b13f227746a4fde696268218e3150ec6e6e 100644
--- a/core/modules/views_ui/tests/src/Functional/AnalyzeTest.php
+++ b/core/modules/views_ui/tests/src/Functional/AnalyzeTest.php
@@ -18,6 +18,11 @@ class AnalyzeTest extends UITestBase {
    */
   public static $modules = ['views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/AreaEntityUITest.php b/core/modules/views_ui/tests/src/Functional/AreaEntityUITest.php
index 4e39164c308f7e72c34cb69d29ce6be5dcb895d4..305315c8027eaa5a352381c407edaae16c5a0df8 100644
--- a/core/modules/views_ui/tests/src/Functional/AreaEntityUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/AreaEntityUITest.php
@@ -19,6 +19,11 @@ class AreaEntityUITest extends UITestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testUI() {
     // Set up a block and a entity_test entity.
     $block = Block::create(['id' => 'test_id', 'plugin' => 'system_main_block']);
diff --git a/core/modules/views_ui/tests/src/Functional/ArgumentValidatorTest.php b/core/modules/views_ui/tests/src/Functional/ArgumentValidatorTest.php
index 5a33970f7b226c3ec162717ce421f52ff52c456e..b5bfe30474a3910c2d239f89a0ef17eaf01b1daf 100644
--- a/core/modules/views_ui/tests/src/Functional/ArgumentValidatorTest.php
+++ b/core/modules/views_ui/tests/src/Functional/ArgumentValidatorTest.php
@@ -18,6 +18,11 @@ class ArgumentValidatorTest extends UITestBase {
    */
   public static $testViews = ['test_argument'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the 'Specify validation criteria' checkbox functionality.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/CachedDataUITest.php b/core/modules/views_ui/tests/src/Functional/CachedDataUITest.php
index 1ef4ca2f95bc5d024013e90023dff249b445cfb3..e50005f49e5f0d71ed1ced2dfc7317ecb65d1f6e 100644
--- a/core/modules/views_ui/tests/src/Functional/CachedDataUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/CachedDataUITest.php
@@ -16,6 +16,11 @@ class CachedDataUITest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the shared tempstore views data in the UI.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/CustomBooleanTest.php b/core/modules/views_ui/tests/src/Functional/CustomBooleanTest.php
index a8219a34b7a1feab14de4c278da91a83a4ad5e3b..5d4dcdea2f630ca36bbefb9bfce8ea92138750fe 100644
--- a/core/modules/views_ui/tests/src/Functional/CustomBooleanTest.php
+++ b/core/modules/views_ui/tests/src/Functional/CustomBooleanTest.php
@@ -20,6 +20,11 @@ class CustomBooleanTest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * \Drupal\views\Tests\ViewTestBase::viewsData().
    */
diff --git a/core/modules/views_ui/tests/src/Functional/DefaultViewsTest.php b/core/modules/views_ui/tests/src/Functional/DefaultViewsTest.php
index 6fe73093ca66716bb11efff6ec796feb0e2a57c9..7a4ad1eaa4d50037d12e459e723d1fa0fd37ffdd 100644
--- a/core/modules/views_ui/tests/src/Functional/DefaultViewsTest.php
+++ b/core/modules/views_ui/tests/src/Functional/DefaultViewsTest.php
@@ -21,6 +21,11 @@ class DefaultViewsTest extends UITestBase {
    */
   public static $testViews = ['test_view_status', 'test_page_display_menu', 'test_page_display_arguments'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views_ui/tests/src/Functional/DisplayAttachmentTest.php b/core/modules/views_ui/tests/src/Functional/DisplayAttachmentTest.php
index 537cedf656eb8a742c27d23fc3bd5566e8873851..bcbf4b709bb3f049baf6dd57fd8175f9beeaf612 100644
--- a/core/modules/views_ui/tests/src/Functional/DisplayAttachmentTest.php
+++ b/core/modules/views_ui/tests/src/Functional/DisplayAttachmentTest.php
@@ -21,6 +21,11 @@ class DisplayAttachmentTest extends UITestBase {
    */
   public static $testViews = ['test_attachment_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the attachment UI.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/DisplayCRUDTest.php b/core/modules/views_ui/tests/src/Functional/DisplayCRUDTest.php
index c1c7cef441cad70ff4df2f9183876a1dfdcd5813..23a355709a301f35dea9000a38b40598d5e68bd3 100644
--- a/core/modules/views_ui/tests/src/Functional/DisplayCRUDTest.php
+++ b/core/modules/views_ui/tests/src/Functional/DisplayCRUDTest.php
@@ -25,6 +25,11 @@ class DisplayCRUDTest extends UITestBase {
    */
   public static $modules = ['contextual'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests adding a display.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/DisplayExtenderUITest.php b/core/modules/views_ui/tests/src/Functional/DisplayExtenderUITest.php
index b222f15d7a69cebc15f2bf3231ab5b939ee943f6..9a4edbc3b6b672dcfa5ee6a259d6c0ff4df646c8 100644
--- a/core/modules/views_ui/tests/src/Functional/DisplayExtenderUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/DisplayExtenderUITest.php
@@ -18,6 +18,11 @@ class DisplayExtenderUITest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the display extender UI.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/DisplayFeedTest.php b/core/modules/views_ui/tests/src/Functional/DisplayFeedTest.php
index 9dba45010f09ba620310921bb8b65908f87ed0d4..8394193df06ec7ad5b8446e7f1a49133f2aafcc1 100644
--- a/core/modules/views_ui/tests/src/Functional/DisplayFeedTest.php
+++ b/core/modules/views_ui/tests/src/Functional/DisplayFeedTest.php
@@ -24,6 +24,11 @@ class DisplayFeedTest extends UITestBase {
    */
   public static $modules = ['views_ui', 'aggregator'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests feed display admin UI.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/DisplayPathTest.php b/core/modules/views_ui/tests/src/Functional/DisplayPathTest.php
index 5973a5d59bfc4bdb1b8e993fdd107ba37ec91344..cdf36704cf35aee75a1805ca2c840b80585a95b5 100644
--- a/core/modules/views_ui/tests/src/Functional/DisplayPathTest.php
+++ b/core/modules/views_ui/tests/src/Functional/DisplayPathTest.php
@@ -27,6 +27,11 @@ protected function setUp($import_test_views = TRUE) {
    */
   public static $modules = ['menu_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/DisplayTest.php b/core/modules/views_ui/tests/src/Functional/DisplayTest.php
index 8fa5a80de387055b3c379ec466992eb12508e3e6..44d74a218594b3ee86ef4ccb0052e76be9b905fe 100644
--- a/core/modules/views_ui/tests/src/Functional/DisplayTest.php
+++ b/core/modules/views_ui/tests/src/Functional/DisplayTest.php
@@ -27,6 +27,11 @@ class DisplayTest extends UITestBase {
    */
   public static $modules = ['contextual'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests adding a display.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/DuplicateTest.php b/core/modules/views_ui/tests/src/Functional/DuplicateTest.php
index 91d88fa60c542c1a59f61f7a5febc75c408c3720..cddd7d666765b9aa14bf1ac71896e9c66ab109d2 100644
--- a/core/modules/views_ui/tests/src/Functional/DuplicateTest.php
+++ b/core/modules/views_ui/tests/src/Functional/DuplicateTest.php
@@ -9,6 +9,11 @@
  */
 class DuplicateTest extends UITestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views_ui/tests/src/Functional/ExposedFormUITest.php b/core/modules/views_ui/tests/src/Functional/ExposedFormUITest.php
index 0822eb833c91fa85443d2330b1ccb8cf0fb52dfb..c863d9362c80b89a77e40d5ec14b58b0ec4bacaa 100644
--- a/core/modules/views_ui/tests/src/Functional/ExposedFormUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/ExposedFormUITest.php
@@ -23,6 +23,11 @@ class ExposedFormUITest extends UITestBase {
    */
   public static $modules = ['node', 'views_ui', 'block', 'taxonomy', 'field_ui', 'datetime'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Array of error message strings raised by the grouped form.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/FieldUITest.php b/core/modules/views_ui/tests/src/Functional/FieldUITest.php
index dc3081f6505fbb97bb2fb2a67eb3c07c74ff1de9..4c52aea7cccc0b2ffbba17d37c679378004b8e1a 100644
--- a/core/modules/views_ui/tests/src/Functional/FieldUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/FieldUITest.php
@@ -13,6 +13,11 @@
  */
 class FieldUITest extends UITestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/FilterBooleanWebTest.php b/core/modules/views_ui/tests/src/Functional/FilterBooleanWebTest.php
index e6adfeea713217abc194d97af862e957bacc3726..f62c8c0ae8867afe0a46ea01eb4ace04537359a9 100644
--- a/core/modules/views_ui/tests/src/Functional/FilterBooleanWebTest.php
+++ b/core/modules/views_ui/tests/src/Functional/FilterBooleanWebTest.php
@@ -17,6 +17,11 @@ class FilterBooleanWebTest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the filter boolean UI.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/FilterNumericWebTest.php b/core/modules/views_ui/tests/src/Functional/FilterNumericWebTest.php
index 8dc568de9bdf2f784b966aa0ded68e39d9433a73..eac88e4dd22ba140c004ee8802318e00a049979e 100644
--- a/core/modules/views_ui/tests/src/Functional/FilterNumericWebTest.php
+++ b/core/modules/views_ui/tests/src/Functional/FilterNumericWebTest.php
@@ -20,6 +20,11 @@ class FilterNumericWebTest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the filter numeric UI.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/FilterUITest.php b/core/modules/views_ui/tests/src/Functional/FilterUITest.php
index 9b7bbcde11879126cf63d03d4cf204fefb7d38fd..6422bb4863ea7a1d68e291081fa6e76b567e7bb6 100644
--- a/core/modules/views_ui/tests/src/Functional/FilterUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/FilterUITest.php
@@ -24,6 +24,11 @@ class FilterUITest extends UITestBase {
    */
   public static $modules = ['views_ui', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/Functional/GroupByTest.php b/core/modules/views_ui/tests/src/Functional/GroupByTest.php
index 6a348b70d4a17f099ac7f301c763d789665c5405..e79ff9d20892b5e7e15638383aed58be394ff912 100644
--- a/core/modules/views_ui/tests/src/Functional/GroupByTest.php
+++ b/core/modules/views_ui/tests/src/Functional/GroupByTest.php
@@ -16,6 +16,11 @@ class GroupByTest extends UITestBase {
    */
   public static $testViews = ['test_views_groupby_save'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests whether basic saving works.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/HandlerTest.php b/core/modules/views_ui/tests/src/Functional/HandlerTest.php
index e37c61f4665e9758b7e0fae64deb938e83355c93..557a9920274a1221851468ec73627cab9a5fe920 100644
--- a/core/modules/views_ui/tests/src/Functional/HandlerTest.php
+++ b/core/modules/views_ui/tests/src/Functional/HandlerTest.php
@@ -21,6 +21,11 @@ class HandlerTest extends UITestBase {
    */
   public static $modules = ['node_test_views'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Views used by this test.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/NewViewConfigSchemaTest.php b/core/modules/views_ui/tests/src/Functional/NewViewConfigSchemaTest.php
index ef493ff8c8945ba8eb96ba1bb7423973fa587cd3..58b0bdfdd938e950621ee1e72e4ba572761719e8 100644
--- a/core/modules/views_ui/tests/src/Functional/NewViewConfigSchemaTest.php
+++ b/core/modules/views_ui/tests/src/Functional/NewViewConfigSchemaTest.php
@@ -16,6 +16,11 @@ class NewViewConfigSchemaTest extends UITestBase {
    */
   public static $modules = ['views_ui', 'node', 'comment', 'file', 'taxonomy', 'dblog', 'aggregator'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests creating brand new views.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php b/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php
index 24116d97ae2afc9ebc862b30bf77d82e1c628d66..1bc982a1c5fa174a33f02a654744a109ea0e3b55 100644
--- a/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php
+++ b/core/modules/views_ui/tests/src/Functional/OverrideDisplaysTest.php
@@ -9,6 +9,11 @@
  */
 class OverrideDisplaysTest extends UITestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function setUp($import_test_views = TRUE) {
     parent::setUp($import_test_views);
 
diff --git a/core/modules/views_ui/tests/src/Functional/PreviewTest.php b/core/modules/views_ui/tests/src/Functional/PreviewTest.php
index b76e464c8c341a50ef0b4b77d6f2d911b2473bc0..a082c89231c88a44b7a88e45e8600f4f95f38eb7 100644
--- a/core/modules/views_ui/tests/src/Functional/PreviewTest.php
+++ b/core/modules/views_ui/tests/src/Functional/PreviewTest.php
@@ -16,6 +16,11 @@ class PreviewTest extends UITestBase {
    */
   public static $testViews = ['test_preview', 'test_preview_error', 'test_pager_full', 'test_mini_pager', 'test_click_sort'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests contextual links in the preview form.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/QueryTest.php b/core/modules/views_ui/tests/src/Functional/QueryTest.php
index 0eb58ce7102df7d0f35b6244ea7acff372e4a730..d806e82262fe7feff48de548cc095e5f93cb39fa 100644
--- a/core/modules/views_ui/tests/src/Functional/QueryTest.php
+++ b/core/modules/views_ui/tests/src/Functional/QueryTest.php
@@ -19,6 +19,11 @@ class QueryTest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/Functional/RearrangeFieldsTest.php b/core/modules/views_ui/tests/src/Functional/RearrangeFieldsTest.php
index 125a7e928b8e1f88a89086d7f58d8e067304fdcb..0ca4b57d194fff482f315fc979acf95df11611b8 100644
--- a/core/modules/views_ui/tests/src/Functional/RearrangeFieldsTest.php
+++ b/core/modules/views_ui/tests/src/Functional/RearrangeFieldsTest.php
@@ -19,6 +19,11 @@ class RearrangeFieldsTest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Gets the fields from the View.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/RedirectTest.php b/core/modules/views_ui/tests/src/Functional/RedirectTest.php
index 4df38cee9e309a959a26dc44218df179f6c8cb17..b332b6a673d99674985c052dc3dbd4741d6cb96c 100644
--- a/core/modules/views_ui/tests/src/Functional/RedirectTest.php
+++ b/core/modules/views_ui/tests/src/Functional/RedirectTest.php
@@ -16,6 +16,11 @@ class RedirectTest extends UITestBase {
    */
   public static $testViews = ['test_view', 'test_redirect_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the redirecting.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/ReportFieldsTest.php b/core/modules/views_ui/tests/src/Functional/ReportFieldsTest.php
index d2527d0b9da43296fd9dd1b804319b852fde3c10..840e91f621061b77978aed3611f8e01d317354d4 100644
--- a/core/modules/views_ui/tests/src/Functional/ReportFieldsTest.php
+++ b/core/modules/views_ui/tests/src/Functional/ReportFieldsTest.php
@@ -17,6 +17,11 @@ class ReportFieldsTest extends UITestBase {
    */
   public static $testViews = ['test_field_field_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/Functional/ReportTest.php b/core/modules/views_ui/tests/src/Functional/ReportTest.php
index e7979930c1f7a61b1957f05c4b517ee16ce3ed29..5322e01084730da88b21ea25178d9a84817fdbcb 100644
--- a/core/modules/views_ui/tests/src/Functional/ReportTest.php
+++ b/core/modules/views_ui/tests/src/Functional/ReportTest.php
@@ -16,6 +16,11 @@ class ReportTest extends UITestBase {
    */
   public static $modules = ['views', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Stores an admin user used by the different tests.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/RowUITest.php b/core/modules/views_ui/tests/src/Functional/RowUITest.php
index 8b256f4373eb391dbab9f29e3308e0d8f4d98cdf..637bbb576d5774ca397cb783cf10d4d127de1f58 100644
--- a/core/modules/views_ui/tests/src/Functional/RowUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/RowUITest.php
@@ -20,6 +20,11 @@ class RowUITest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests changing the row plugin and changing some options of a row.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/SettingsTest.php b/core/modules/views_ui/tests/src/Functional/SettingsTest.php
index 1ac98c6e634f702a7103865475829e3d2d6828b7..d5ce503523f17e273e3f910f2b6e16df83557877 100644
--- a/core/modules/views_ui/tests/src/Functional/SettingsTest.php
+++ b/core/modules/views_ui/tests/src/Functional/SettingsTest.php
@@ -16,6 +16,11 @@ class SettingsTest extends UITestBase {
    */
   protected $adminUser;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/Functional/StorageTest.php b/core/modules/views_ui/tests/src/Functional/StorageTest.php
index 02f4fc77df7c2c5dd2333f0dd830daf83c26d71a..86708a93028a778ec3627fd14727158648575f12 100644
--- a/core/modules/views_ui/tests/src/Functional/StorageTest.php
+++ b/core/modules/views_ui/tests/src/Functional/StorageTest.php
@@ -20,6 +20,11 @@ class StorageTest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Modules to enable.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/StyleTableTest.php b/core/modules/views_ui/tests/src/Functional/StyleTableTest.php
index d00df330227439f3d0641cf15eabf4c27e0bf449..3efbbb7355ea8dc50191c3c33ce301bb7ab544b1 100644
--- a/core/modules/views_ui/tests/src/Functional/StyleTableTest.php
+++ b/core/modules/views_ui/tests/src/Functional/StyleTableTest.php
@@ -12,6 +12,11 @@
  */
 class StyleTableTest extends UITestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests created a table style view.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/StyleUITest.php b/core/modules/views_ui/tests/src/Functional/StyleUITest.php
index 62f682a5f9255c7f48eaa0b4599646bd42c43adc..0bd7e98639c21bfbc31324d79126c37d0df80101 100644
--- a/core/modules/views_ui/tests/src/Functional/StyleUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/StyleUITest.php
@@ -19,6 +19,11 @@ class StyleUITest extends UITestBase {
    */
   public static $testViews = ['test_view'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests changing the style plugin and changing some options of a style.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/TokenizeAreaUITest.php b/core/modules/views_ui/tests/src/Functional/TokenizeAreaUITest.php
index df42d8e11d33193f9f0bde5f6a70cee1603f7125..3a8bea6fae077fea28248881e2e536c7f60a7807 100644
--- a/core/modules/views_ui/tests/src/Functional/TokenizeAreaUITest.php
+++ b/core/modules/views_ui/tests/src/Functional/TokenizeAreaUITest.php
@@ -18,6 +18,11 @@ class TokenizeAreaUITest extends UITestBase {
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test that the right tokens are shown as available for replacement.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/TranslatedViewTest.php b/core/modules/views_ui/tests/src/Functional/TranslatedViewTest.php
index a8d3c8b96f514084c8890c09d4067f38e34958d3..d3c521b5eae07ba1b05c111d64422758eb861482 100644
--- a/core/modules/views_ui/tests/src/Functional/TranslatedViewTest.php
+++ b/core/modules/views_ui/tests/src/Functional/TranslatedViewTest.php
@@ -21,6 +21,11 @@ class TranslatedViewTest extends UITestBase {
     'views_ui',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Languages to enable.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/UnsavedPreviewTest.php b/core/modules/views_ui/tests/src/Functional/UnsavedPreviewTest.php
index 3265e1a2f564e5b7a72e7bcec42141cd143dcab2..96c3778446a902993a679c50b2d437ccb2321506 100644
--- a/core/modules/views_ui/tests/src/Functional/UnsavedPreviewTest.php
+++ b/core/modules/views_ui/tests/src/Functional/UnsavedPreviewTest.php
@@ -16,6 +16,11 @@ class UnsavedPreviewTest extends UITestBase {
     */
   public static $testViews = ['content'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An admin user with the 'administer views' permission.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/ViewEditTest.php b/core/modules/views_ui/tests/src/Functional/ViewEditTest.php
index 645bac54a81790ed7a6f5fba74b20caaa7949597..82eec0b60d3cce6a0d5c76d84133f6bd4c2f0fef 100644
--- a/core/modules/views_ui/tests/src/Functional/ViewEditTest.php
+++ b/core/modules/views_ui/tests/src/Functional/ViewEditTest.php
@@ -19,6 +19,11 @@ class ViewEditTest extends UITestBase {
    */
   public static $testViews = ['test_view', 'test_display', 'test_groupwise_term_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the delete link on a views UI.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/ViewsListTest.php b/core/modules/views_ui/tests/src/Functional/ViewsListTest.php
index 956ab9bc0cb9be3983eaf330a0f43dfcd14f6934..80ac1b8d00398c8ad903f6861272dccca701bf06 100644
--- a/core/modules/views_ui/tests/src/Functional/ViewsListTest.php
+++ b/core/modules/views_ui/tests/src/Functional/ViewsListTest.php
@@ -19,6 +19,11 @@ class ViewsListTest extends UITestBase {
    */
   public static $modules = ['block', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A user with permission to administer views.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/ViewsUITourTest.php b/core/modules/views_ui/tests/src/Functional/ViewsUITourTest.php
index 8a2dd2953f3b20c1a858d5a7f30975da94e7c69e..2dd089da7b3c1c77fe3ed2b071d787a38a9f7b49 100644
--- a/core/modules/views_ui/tests/src/Functional/ViewsUITourTest.php
+++ b/core/modules/views_ui/tests/src/Functional/ViewsUITourTest.php
@@ -19,6 +19,11 @@ class ViewsUITourTest extends TourTestBase {
    */
   protected $adminUser;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * String translation storage object.
    *
diff --git a/core/modules/views_ui/tests/src/Functional/WizardTest.php b/core/modules/views_ui/tests/src/Functional/WizardTest.php
index 81154817ef9933aeb6a8a18052418d8e9a7a77cf..855efeddc1dfee84da9864d93c19427a5d7eb3fc 100644
--- a/core/modules/views_ui/tests/src/Functional/WizardTest.php
+++ b/core/modules/views_ui/tests/src/Functional/WizardTest.php
@@ -14,6 +14,11 @@
  */
 class WizardTest extends WizardTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests filling in the wizard with really long strings.
    */
diff --git a/core/modules/views_ui/tests/src/Functional/XssTest.php b/core/modules/views_ui/tests/src/Functional/XssTest.php
index cabb48ebcfe3a1ea82c54980d0b7787b6cb26b4d..3e7fc34b14e130b27d3d468c3231bc0426edf1bf 100644
--- a/core/modules/views_ui/tests/src/Functional/XssTest.php
+++ b/core/modules/views_ui/tests/src/Functional/XssTest.php
@@ -16,6 +16,11 @@ class XssTest extends UITestBase {
    */
   public static $modules = ['node', 'user', 'views_ui', 'views_ui_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testViewsUi() {
     $this->drupalGet('admin/structure/views/view/sa_contrib_2013_035');
     $this->assertEscaped('<marquee>test</marquee>', 'Field admin label is properly escaped.');
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/DisplayTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/DisplayTest.php
index 6b7cd1226f88b7fb0215af123a57f27448a9b822..799bb876214184366597fb2bdb94b1b12ece712b 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/DisplayTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/DisplayTest.php
@@ -28,6 +28,11 @@ class DisplayTest extends WebDriverTestBase {
     'views_test_config',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   public static $testViews = ['test_content_ajax', 'test_display'];
 
   /**
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/FilterCriteriaTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/FilterCriteriaTest.php
index f12c4784320dbfb9afb8c2fcccc45148e39134a5..1f28058fa99c9cf5a2677f090e539316769966a8 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/FilterCriteriaTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/FilterCriteriaTest.php
@@ -16,6 +16,11 @@ class FilterCriteriaTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/FilterOptionsTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/FilterOptionsTest.php
index 6f2f6259682d1f05dce940f528864cdc9afb5815..69c9021e172a40e56fc266c899bb03e0428dbd21 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/FilterOptionsTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/FilterOptionsTest.php
@@ -16,6 +16,11 @@ class FilterOptionsTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui', 'views_ui_test_field'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/LibraryCachingTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/LibraryCachingTest.php
index b1b158ba6ce30b4f1b3567e07994651921b6acee..c4e14c63cf299468f1220038d91fff39ee8ffe8d 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/LibraryCachingTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/LibraryCachingTest.php
@@ -16,6 +16,11 @@ class LibraryCachingTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if the Views UI dialogs open on consecutive requests.
    */
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php
index 489a3748df44a59498cf0630ea6cfea359367530..ae33591b102a12179954eaa6046a7d8dabd25ba0 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/PreviewTest.php
@@ -31,6 +31,11 @@ class PreviewTest extends WebDriverTestBase {
     'views_test_config',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsListingTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsListingTest.php
index fc696c03a866ff0097613063b1fe7280f33ddf0d..f6a9976dcf9a1ba4fdc7cfb152fb037785340419 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsListingTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsListingTest.php
@@ -17,6 +17,11 @@ class ViewsListingTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsWizardTest.php b/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsWizardTest.php
index 16369f12fea1ce1804003ab5a9f5fbdeda93b911..33611fbe1e5a61e922c480404523ec2911793139 100644
--- a/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsWizardTest.php
+++ b/core/modules/views_ui/tests/src/FunctionalJavascript/ViewsWizardTest.php
@@ -17,6 +17,11 @@ class ViewsWizardTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'views', 'views_ui', 'block', 'user'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonAnonTest.php b/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonAnonTest.php
index 0c2fe0046325d25847794852abf888e2f550f213..741970775c112c4cb829b772de9311bbf6b2c13f 100644
--- a/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonAnonTest.php
+++ b/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class WorkflowHalJsonAnonTest extends WorkflowResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonBasicAuthTest.php b/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonBasicAuthTest.php
index b2e9807333a7b86e51b4a09a735898ca9c27a60e..2a9c18bf165eba8783eab555bd17aaffa10351c8 100644
--- a/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonBasicAuthTest.php
+++ b/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class WorkflowHalJsonBasicAuthTest extends WorkflowHalJsonAnonTest {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonCookieTest.php b/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonCookieTest.php
index 94199e5fa4825d8670867e8b1bc74bf8ae012147..db1a75c1d1202542c1c5aaa79fabb311208c8113 100644
--- a/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonCookieTest.php
+++ b/core/modules/workflows/tests/src/Functional/Hal/WorkflowHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class WorkflowHalJsonCookieTest extends WorkflowHalJsonAnonTest {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonAnonTest.php b/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonAnonTest.php
index edb7d0b556e7953da1c2dcf4eb0b8a638045a766..4865353f8f54d01d08550f73350b77f7d21dae8c 100644
--- a/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonAnonTest.php
+++ b/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonAnonTest.php
@@ -21,4 +21,9 @@ class WorkflowJsonAnonTest extends WorkflowResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonBasicAuthTest.php b/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonBasicAuthTest.php
index db687cfbb48b5afe11d4996695644d6312179f48..0c979d6d6e2f19da99021c89708ccf01a909ce2f 100644
--- a/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonBasicAuthTest.php
+++ b/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class WorkflowJsonBasicAuthTest extends WorkflowResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonCookieTest.php b/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonCookieTest.php
index 19bd342503fd3a7fbb2352d7295bf13678506858..42165deb536b5f451e75f81f77a666e745a6ea99 100644
--- a/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonCookieTest.php
+++ b/core/modules/workflows/tests/src/Functional/Rest/WorkflowJsonCookieTest.php
@@ -26,4 +26,9 @@ class WorkflowJsonCookieTest extends WorkflowResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlAnonTest.php b/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlAnonTest.php
index a66cc7763bf12a535526f5c5ee04bb4da8de5007..dbd938d23009a4a54a58cd67bd04a80d0c9e0a79 100644
--- a/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlAnonTest.php
+++ b/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlAnonTest.php
@@ -23,4 +23,9 @@ class WorkflowXmlAnonTest extends WorkflowResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlBasicAuthTest.php b/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlBasicAuthTest.php
index db443e4763cdf1a360507c9ca79828ef5ba5f520..0f1bbb721915670e9dea934c4cb272eabc9ffd19 100644
--- a/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlBasicAuthTest.php
+++ b/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class WorkflowXmlBasicAuthTest extends WorkflowResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlCookieTest.php b/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlCookieTest.php
index 50ea707ba8b4fef9f5975c0d290aedcef5ec500b..e5ad8f6d790b68c67207f531e2f799fb37ff8908 100644
--- a/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlCookieTest.php
+++ b/core/modules/workflows/tests/src/Functional/Rest/WorkflowXmlCookieTest.php
@@ -28,4 +28,9 @@ class WorkflowXmlCookieTest extends WorkflowResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/workflows/tests/src/Functional/WorkflowCustomStateTransitionAccessTest.php b/core/modules/workflows/tests/src/Functional/WorkflowCustomStateTransitionAccessTest.php
index 327b17255816aa87a9fc16cd1a5d31ff8d0a77c2..c0b044ed791f28df86640eab073a12eda35dc238 100644
--- a/core/modules/workflows/tests/src/Functional/WorkflowCustomStateTransitionAccessTest.php
+++ b/core/modules/workflows/tests/src/Functional/WorkflowCustomStateTransitionAccessTest.php
@@ -20,6 +20,11 @@ class WorkflowCustomStateTransitionAccessTest extends BrowserTestBase {
     'workflow_type_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A test admin user.
    *
diff --git a/core/modules/workflows/tests/src/Functional/WorkflowUiNoTypeTest.php b/core/modules/workflows/tests/src/Functional/WorkflowUiNoTypeTest.php
index 01c61ac6b00d6cc117f656f8e01a53bc2d81417e..94c862e6b4ef775b065eafaa0c55433aa5c498d7 100644
--- a/core/modules/workflows/tests/src/Functional/WorkflowUiNoTypeTest.php
+++ b/core/modules/workflows/tests/src/Functional/WorkflowUiNoTypeTest.php
@@ -18,6 +18,11 @@ class WorkflowUiNoTypeTest extends BrowserTestBase {
    */
   public static $modules = ['workflows', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php b/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php
index 227ddd769a0c5d31f0a091f10d77a5911d44bc3e..5a6fa195a9e4f0963aae1a2ad28f1bceb4630631 100644
--- a/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php
+++ b/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php
@@ -20,6 +20,11 @@ class WorkflowUiTest extends BrowserTestBase {
    */
   public static $modules = ['workflows', 'workflow_type_test', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonAnonTest.php b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonAnonTest.php
index f44286f1262a43728415c2565e93f8e2b012daaf..17c0e7ea0800a9bedf16c3d6b37a11f5e6087104 100644
--- a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonAnonTest.php
+++ b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonAnonTest.php
@@ -23,4 +23,9 @@ class WorkspaceJsonAnonTest extends WorkspaceResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonBasicAuthTest.php b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonBasicAuthTest.php
index 8be512a7935d24ea6b2c5848ce9da84ed6f5f7c2..c8721232eb9246834fc7b7019908949fda1da873 100644
--- a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonBasicAuthTest.php
+++ b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonBasicAuthTest.php
@@ -18,6 +18,11 @@ class WorkspaceJsonBasicAuthTest extends WorkspaceResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonCookieTest.php b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonCookieTest.php
index dfba4aeeb596ba699e3208e8018097e7632c683e..f7c230df2ca975f017e82651e5b3f8cf75b85add 100644
--- a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonCookieTest.php
+++ b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceJsonCookieTest.php
@@ -28,4 +28,9 @@ class WorkspaceJsonCookieTest extends WorkspaceResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlAnonTest.php b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlAnonTest.php
index c87b438a2321af2ab0bfa7948c6ad8bcef89a381..c2c5f3c5d4e321b38adc036a9104233dd479f114 100644
--- a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlAnonTest.php
+++ b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlAnonTest.php
@@ -25,6 +25,11 @@ class WorkspaceXmlAnonTest extends WorkspaceResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlBasicAuthTest.php b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlBasicAuthTest.php
index 8769d9e8bac130409b2bc6bc43973c1693f2f37d..8ba105cb82fcf26b8cb276f6afda43d2f1c4dcb9 100644
--- a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlBasicAuthTest.php
+++ b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlBasicAuthTest.php
@@ -20,6 +20,11 @@ class WorkspaceXmlBasicAuthTest extends WorkspaceResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlCookieTest.php b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlCookieTest.php
index c37a28376d051b84dc02f1d9b46de8f0c9afd39c..c7066a8dadaf0c03b90be6414da906b9258a01bc 100644
--- a/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlCookieTest.php
+++ b/core/modules/workspaces/tests/src/Functional/EntityResource/WorkspaceXmlCookieTest.php
@@ -30,6 +30,11 @@ class WorkspaceXmlCookieTest extends WorkspaceResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workspaces/tests/src/Functional/PathWorkspacesTest.php b/core/modules/workspaces/tests/src/Functional/PathWorkspacesTest.php
index 78ae786c52768b8b8b40de4b5a785d3421683ecd..1787815b1f6047f0f4f3ff58f32db909560d8861 100644
--- a/core/modules/workspaces/tests/src/Functional/PathWorkspacesTest.php
+++ b/core/modules/workspaces/tests/src/Functional/PathWorkspacesTest.php
@@ -21,6 +21,11 @@ class PathWorkspacesTest extends BrowserTestBase {
    */
   protected static $modules = ['block', 'content_translation', 'node', 'path', 'workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspaceBypassTest.php b/core/modules/workspaces/tests/src/Functional/WorkspaceBypassTest.php
index cbed0a5f3288ddfc65f1321323395f18a33e1e31..ce5aeceeb00ee540b7335e2050d860ef5e28ed66 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspaceBypassTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspaceBypassTest.php
@@ -20,6 +20,11 @@ class WorkspaceBypassTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'user', 'block', 'workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verifies that a user can edit anything in a workspace they own.
    */
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspaceCacheContextTest.php b/core/modules/workspaces/tests/src/Functional/WorkspaceCacheContextTest.php
index 8945a69176cdeaba2222fab697190c9b0be23f37..517e6b8d71045c655b5d20aa848194a03a8d2061 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspaceCacheContextTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspaceCacheContextTest.php
@@ -22,6 +22,11 @@ class WorkspaceCacheContextTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'node', 'workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the 'workspace' cache context.
    */
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspaceConcurrentEditingTest.php b/core/modules/workspaces/tests/src/Functional/WorkspaceConcurrentEditingTest.php
index 43e04f0d5ac9c5c902108bd302de82e3c821fc0d..6b53ae4109b2ccbb3edfb392f060d0ff9c9b043c 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspaceConcurrentEditingTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspaceConcurrentEditingTest.php
@@ -18,6 +18,11 @@ class WorkspaceConcurrentEditingTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'node', 'workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test editing a node in multiple workspaces.
    */
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspacePermissionsTest.php b/core/modules/workspaces/tests/src/Functional/WorkspacePermissionsTest.php
index c70ceeac6688556c93d4c6e7969108bdc1b92fad..99d2b0aaf40958cfaecd907bcafdde474505f1f7 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspacePermissionsTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspacePermissionsTest.php
@@ -19,6 +19,11 @@ class WorkspacePermissionsTest extends BrowserTestBase {
    */
   public static $modules = ['workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verifies that a user can create but not edit a workspace.
    */
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspaceSwitcherTest.php b/core/modules/workspaces/tests/src/Functional/WorkspaceSwitcherTest.php
index 63d7d8609f2475f01eda76c5c0e8d87dd63c4bd1..7c8c8fa30f377185896f6707c78056db322b59d2 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspaceSwitcherTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspaceSwitcherTest.php
@@ -20,6 +20,11 @@ class WorkspaceSwitcherTest extends BrowserTestBase {
    */
   public static $modules = ['block', 'workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspaceTest.php b/core/modules/workspaces/tests/src/Functional/WorkspaceTest.php
index a0f887706172d909a2f5d3a2818cd97b7918ac55..5fb3b6792b644bcd21187f03dcda802359149f33 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspaceTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspaceTest.php
@@ -18,6 +18,11 @@ class WorkspaceTest extends BrowserTestBase {
    */
   public static $modules = ['workspaces', 'toolbar', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A test user.
    *
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspaceViewTest.php b/core/modules/workspaces/tests/src/Functional/WorkspaceViewTest.php
index df1b3c8c57f04119f9fb057541096c05d73bdd2e..7468511990a2b10aacfad80b6b84ef7988cd8c61 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspaceViewTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspaceViewTest.php
@@ -19,6 +19,11 @@ class WorkspaceViewTest extends BrowserTestBase {
    */
   public static $modules = ['workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verifies that a user can view their own workspace.
    */
diff --git a/core/modules/workspaces/tests/src/Functional/WorkspacesUninstallTest.php b/core/modules/workspaces/tests/src/Functional/WorkspacesUninstallTest.php
index 7e09248c0b5d638c57d0cce438358a868e665d41..975bacabf97fdb472292f35b786d2a4f7722d5b2 100644
--- a/core/modules/workspaces/tests/src/Functional/WorkspacesUninstallTest.php
+++ b/core/modules/workspaces/tests/src/Functional/WorkspacesUninstallTest.php
@@ -21,6 +21,11 @@ class WorkspacesUninstallTest extends BrowserTestBase {
    */
   public static $modules = ['workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests deleting workspace entities and uninstalling Workspaces module.
    */
diff --git a/core/modules/workspaces/tests/src/FunctionalJavascript/WorkspaceToolbarIntegrationTest.php b/core/modules/workspaces/tests/src/FunctionalJavascript/WorkspaceToolbarIntegrationTest.php
index c0eb05728092af6d1c675bf65ac63d4b58d55e30..889f50261ab01291b39a624a2c5e5e9b4680dd80 100644
--- a/core/modules/workspaces/tests/src/FunctionalJavascript/WorkspaceToolbarIntegrationTest.php
+++ b/core/modules/workspaces/tests/src/FunctionalJavascript/WorkspaceToolbarIntegrationTest.php
@@ -16,6 +16,11 @@ class WorkspaceToolbarIntegrationTest extends OffCanvasTestBase {
    */
   public static $modules = ['toolbar', 'workspaces'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/profiles/demo_umami/modules/demo_umami_content/tests/src/Functional/DefaultContentFilesAccessTest.php b/core/profiles/demo_umami/modules/demo_umami_content/tests/src/Functional/DefaultContentFilesAccessTest.php
index cda82219f46ce088322987b1632b42d8b9ae79eb..4a176df14b512b5c46e26c66d21c95b9f5e38a0c 100644
--- a/core/profiles/demo_umami/modules/demo_umami_content/tests/src/Functional/DefaultContentFilesAccessTest.php
+++ b/core/profiles/demo_umami/modules/demo_umami_content/tests/src/Functional/DefaultContentFilesAccessTest.php
@@ -11,6 +11,11 @@
  */
 class DefaultContentFilesAccessTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that sample images, recipes and articles are not accessible.
    */
diff --git a/core/profiles/minimal/tests/src/Functional/MinimalTest.php b/core/profiles/minimal/tests/src/Functional/MinimalTest.php
index d743fee5f434ab79de3712e8660ecd0e7324074b..b0c587e937a7a9f55f6cf28edfb1cfda99aa3636 100644
--- a/core/profiles/minimal/tests/src/Functional/MinimalTest.php
+++ b/core/profiles/minimal/tests/src/Functional/MinimalTest.php
@@ -17,6 +17,11 @@ class MinimalTest extends BrowserTestBase {
 
   protected $profile = 'minimal';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests Minimal installation profile.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxCallbacksTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxCallbacksTest.php
index ffdbd98eb91dc1eafb45a547c6d8d9dc19f28577..26e2343601bd4493c7e1a565c69df365fd74eade 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxCallbacksTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxCallbacksTest.php
@@ -16,6 +16,11 @@ class AjaxCallbacksTest extends WebDriverTestBase {
    */
   public static $modules = ['ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if Ajax callback works on date element.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php
index 52e095267e769eb9d759c728304a0413a8c3034e..00f01d75145024f93250dc9cb02639e2a49d1d57 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormCacheTest.php
@@ -19,6 +19,11 @@ class AjaxFormCacheTest extends WebDriverTestBase {
    */
   public static $modules = ['ajax_test', 'ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the usage of form cache for AJAX forms.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormImageButtonTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormImageButtonTest.php
index 0865b79766a0aeeeb03f24f114fe98d9a84d3bec..64034733cea41e75aae545a6469f2a2c49738ce8 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormImageButtonTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormImageButtonTest.php
@@ -16,6 +16,11 @@ class AjaxFormImageButtonTest extends WebDriverTestBase {
    */
   public static $modules = ['ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests image buttons can be operated with the keyboard ENTER key.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php
index 5a167f729cb92263eed2968543ec0f9a70afc4ef..1ac000ce74daa20d02c6711e49e848d478ad4cbc 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php
@@ -16,6 +16,11 @@ class AjaxFormPageCacheTest extends WebDriverTestBase {
    */
   public static $modules = ['ajax_test', 'ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxInGroupTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxInGroupTest.php
index d70b68d8e510e7c2fa229bb40cd2e10383627ce5..a6bf4f2f445794d3652c7e91605a09ab15465e8c 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxInGroupTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxInGroupTest.php
@@ -16,6 +16,11 @@ class AjaxInGroupTest extends WebDriverTestBase {
    */
   protected static $modules = ['ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
index 5d11ce49b4bc758fffdb8864cc3af79f94d4b94d..87e2f88cd5b38244cb49e9677d8edd203b9e5c58 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
@@ -16,6 +16,11 @@ class AjaxTest extends WebDriverTestBase {
    */
   public static $modules = ['ajax_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testAjaxWithAdminRoute() {
     \Drupal::service('theme_installer')->install(['stable', 'seven']);
     $theme_config = \Drupal::configFactory()->getEditable('system.theme');
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/BackwardCompatibilityTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/BackwardCompatibilityTest.php
index 9a45583b7c2cbdb6c2f0007a32654043a7fda78c..4c2b94d9ed6dd0b510993efdd803ab737f388f50 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/BackwardCompatibilityTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/BackwardCompatibilityTest.php
@@ -18,6 +18,11 @@ class BackwardCompatibilityTest extends WebDriverTestBase {
     'js_ajax_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensures Drupal.Ajax.element_settings BC layer.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/CommandsTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/CommandsTest.php
index eca511d82239b4b63127f7bfe483b84b59341ade..8dee3fed6963ed184765720044ebf76bbdf92e69 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/CommandsTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/CommandsTest.php
@@ -16,6 +16,11 @@ class CommandsTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'ajax_test', 'ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests the various Ajax Commands.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/DialogTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/DialogTest.php
index b0c655190d88c316ae9027012a992db52cbfa755..e6f7c666e10babbf9014f42929c25571854082ad 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/DialogTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/DialogTest.php
@@ -18,6 +18,11 @@ class DialogTest extends WebDriverTestBase {
    */
   protected static $modules = ['ajax_test', 'ajax_forms_test', 'contact'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Test sending non-JS and AJAX requests to open and manipulate modals.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ElementValidationTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ElementValidationTest.php
index 48bda56cdf930d02fd4f3f492400267220e7a90f..ad85e98b2a099c5a6ca8e551bb523771a920ce89 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ElementValidationTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ElementValidationTest.php
@@ -16,6 +16,11 @@ class ElementValidationTest extends WebDriverTestBase {
    */
   public static $modules = ['ajax_test', 'ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tries to post an Ajax change to a form that has a validated element.
    *
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/FormValuesTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/FormValuesTest.php
index d1a3e5c2b92c82b0bce64d718d43878b478ac1a0..0911bbe1d7e2d47b03b87b4e18c86538519ede1f 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/FormValuesTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/FormValuesTest.php
@@ -16,6 +16,11 @@ class FormValuesTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'ajax_test', 'ajax_forms_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MessageCommandTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MessageCommandTest.php
index 22cbbab76efbbbff307d892e2e470f9e461d71e7..04b824c57483e6f84f8de62a9d0c7cdee46fccf7 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MessageCommandTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MessageCommandTest.php
@@ -16,6 +16,11 @@ class MessageCommandTest extends WebDriverTestBase {
    */
   protected static $modules = ['ajax_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test AJAX MessageCommand use in a form.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MultiFormTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MultiFormTest.php
index 283223537c1b3f3e91de59a9e511861567d43304..0a1547f8f531385d09da58cd1b9dd5afbe14dd6e 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MultiFormTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MultiFormTest.php
@@ -21,6 +21,11 @@ class MultiFormTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ThrobberTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ThrobberTest.php
index 3ece94942b67a36e553ec73098d72e4f5d6af32e..d64e4f1b766b4a400f9249296f007a6c845fcf57 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ThrobberTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/ThrobberTest.php
@@ -22,6 +22,11 @@ class ThrobberTest extends WebDriverTestBase {
     'hold_test',
   ];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/BrowserWithJavascriptTest.php b/core/tests/Drupal/FunctionalJavascriptTests/BrowserWithJavascriptTest.php
index 76454f741c7698c01ee861f17206123b4e46601d..672b0488ff42001f5841811fa5a72ed872847900 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/BrowserWithJavascriptTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/BrowserWithJavascriptTest.php
@@ -19,6 +19,11 @@ class BrowserWithJavascriptTest extends WebDriverTestBase {
    */
   public static $modules = ['test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testJavascript() {
     $this->drupalGet('<front>');
     $session = $this->getSession();
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php
index 1c76c26ea350b2fff36bdef059b2fef9eceae09b..20acd677de54212af2b5e96c55606e7edc7bf678 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/FormGroupingElementsTest.php
@@ -18,6 +18,11 @@ class FormGroupingElementsTest extends WebDriverTestBase {
    */
   public static $modules = ['form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
index 89c0b1ec024eb3fd78f6105bf5c599c7e2d528e1..b99f32da140866a772fcece0e1481c09919fd328 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
@@ -17,6 +17,11 @@ class JsMessageTest extends WebDriverTestBase {
    */
   public static $modules = ['js_message_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Core/MachineNameTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/MachineNameTest.php
index 4396a8b6e34d10fbc3bd6de182bd736887da30b0..aaa9440e75b619aa8147f465afab29eb3983a608 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Core/MachineNameTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/MachineNameTest.php
@@ -21,6 +21,11 @@ class MachineNameTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'form_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Core/Session/SessionTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/Session/SessionTest.php
index f4a180038242fb9917faa20eff10bdde3874a246..1ba1132bcfcc4313b0eb7223f1a43f6a5158caee 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Core/Session/SessionTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/Session/SessionTest.php
@@ -17,6 +17,11 @@ class SessionTest extends WebDriverTestBase {
    */
   public static $modules = ['menu_link_content', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Dialog/DialogPositionTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Dialog/DialogPositionTest.php
index 4bfe3e0b3ae18525eda8770e325791ea5ad3bd5f..280682341a54cfcd1d05b84f4040932beb2c4d04 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Dialog/DialogPositionTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Dialog/DialogPositionTest.php
@@ -16,6 +16,11 @@ class DialogPositionTest extends WebDriverTestBase {
    */
   public static $modules = ['block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests if the dialog UI works properly with block layout page.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
index fe4c9cf6c6434757660c504465e8ff838e57b8c1..0b86802c98a399084798467227d40f4821443411 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
@@ -23,6 +23,11 @@ class EntityReferenceAutocompleteWidgetTest extends WebDriverTestBase {
    */
   public static $modules = ['node', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptGetDrupalSettingsTest.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptGetDrupalSettingsTest.php
index 72ab2e24c4b76ac89734d7ddf7664ecacbc4da51..3016dd14682541ea1c9a2124970d7b2ec3eba777 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptGetDrupalSettingsTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptGetDrupalSettingsTest.php
@@ -14,6 +14,11 @@ class JavascriptGetDrupalSettingsTest extends WebDriverTestBase {
    */
   protected static $modules = ['test_page_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests retrieval of Drupal settings.
    *
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/TableDrag/TableDragTest.php b/core/tests/Drupal/FunctionalJavascriptTests/TableDrag/TableDragTest.php
index ee7fe96c2ba37a4f4bf10ee03d2f0091c5ce11c3..d9fa93034289a346fb6c9cd6e232d3ae0921972c 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/TableDrag/TableDragTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/TableDrag/TableDragTest.php
@@ -22,6 +22,11 @@ class TableDragTest extends WebDriverTestBase {
    */
   protected static $modules = ['tabledrag_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The state service.
    *
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Tests/DrupalSelenium2DriverTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Tests/DrupalSelenium2DriverTest.php
index 02fcc6ebaf6eb516364495ed3a20089eaeb2e1d9..687cbca4cabef095735ad48d70613f837c66eb24 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Tests/DrupalSelenium2DriverTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Tests/DrupalSelenium2DriverTest.php
@@ -23,6 +23,11 @@ class DrupalSelenium2DriverTest extends WebDriverTestBase {
    */
   protected static $modules = ['file', 'field_ui', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebAssertTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebAssertTest.php
index fa3a3d1aac23ea03cb455ba246a530f866b19d30..14deebe63b7695d572d0719a5eda2768dbce08e2 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebAssertTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebAssertTest.php
@@ -20,6 +20,11 @@ class JSWebAssertTest extends WebDriverTestBase {
    */
   public static $modules = ['js_webassert_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that JSWebAssert assertions work correctly.
    */
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebWithWebDriverAssertTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebWithWebDriverAssertTest.php
index d31a9a51c3fdbe8672dc87cdf65ba974d6addff7..18840e2a893aa1c0367ed4df4fd098ad65d515e1 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebWithWebDriverAssertTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebWithWebDriverAssertTest.php
@@ -16,4 +16,9 @@ class JSWebWithWebDriverAssertTest extends JSWebAssertTest {
    */
   protected $minkDefaultDriverClass = DrupalSelenium2Driver::class;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Bootstrap/UncaughtExceptionTest.php b/core/tests/Drupal/FunctionalTests/Bootstrap/UncaughtExceptionTest.php
index 1a0f19e971d78b3678e6a3b7354556b299b94373..61a6f2db04d0548169be2f1f16d4f319d785334d 100644
--- a/core/tests/Drupal/FunctionalTests/Bootstrap/UncaughtExceptionTest.php
+++ b/core/tests/Drupal/FunctionalTests/Bootstrap/UncaughtExceptionTest.php
@@ -40,6 +40,11 @@ class UncaughtExceptionTest extends BrowserTestBase {
    */
   public static $modules = ['error_service_test', 'error_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Breadcrumb/Breadcrumb404Test.php b/core/tests/Drupal/FunctionalTests/Breadcrumb/Breadcrumb404Test.php
index b29f2630c6c90eda28c6dfdd190b67d53a337a40..ef06f3a3fc373278037dea671cf22a9db891f7df 100644
--- a/core/tests/Drupal/FunctionalTests/Breadcrumb/Breadcrumb404Test.php
+++ b/core/tests/Drupal/FunctionalTests/Breadcrumb/Breadcrumb404Test.php
@@ -19,6 +19,11 @@ class Breadcrumb404Test extends BrowserTestBase {
    */
   public static $modules = ['system', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that different 404s don't create unnecessary cache entries.
    */
diff --git a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
index 3a94bddd76e64f687f4e49108a42bd316de69377..95a84babaf7ff6b42d3d16f7f11bc26bfcb95e84 100644
--- a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
+++ b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
@@ -26,6 +26,11 @@ class BrowserTestBaseTest extends BrowserTestBase {
    */
   public static $modules = ['test_page_test', 'form_test', 'system_test', 'node'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Tests basic page test.
    */
diff --git a/core/tests/Drupal/FunctionalTests/BrowserTestBaseUserAgentTest.php b/core/tests/Drupal/FunctionalTests/BrowserTestBaseUserAgentTest.php
index 8468fd5af831be115894dcbfe91260dadbb86ea2..ac6d760635253b5ff7a14e43788434fa965473e1 100644
--- a/core/tests/Drupal/FunctionalTests/BrowserTestBaseUserAgentTest.php
+++ b/core/tests/Drupal/FunctionalTests/BrowserTestBaseUserAgentTest.php
@@ -11,6 +11,11 @@
  */
 class BrowserTestBaseUserAgentTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The user agent string to use.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Core/Config/SchemaConfigListenerTest.php b/core/tests/Drupal/FunctionalTests/Core/Config/SchemaConfigListenerTest.php
index 698a7d1a0347c31430b8a3b362774f28ef576779..b0061f4f7bfb41186c4ba3bad841d7c545d5d006 100644
--- a/core/tests/Drupal/FunctionalTests/Core/Config/SchemaConfigListenerTest.php
+++ b/core/tests/Drupal/FunctionalTests/Core/Config/SchemaConfigListenerTest.php
@@ -19,4 +19,9 @@ class SchemaConfigListenerTest extends BrowserTestBase {
    */
   public static $modules = ['config_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Core/Test/ModuleInstallBatchTest.php b/core/tests/Drupal/FunctionalTests/Core/Test/ModuleInstallBatchTest.php
index 60c4356c391d918b84224fa2a8a021e88b43a3aa..dc02499d5138a6ace1281124df148dab0547785e 100644
--- a/core/tests/Drupal/FunctionalTests/Core/Test/ModuleInstallBatchTest.php
+++ b/core/tests/Drupal/FunctionalTests/Core/Test/ModuleInstallBatchTest.php
@@ -25,6 +25,11 @@ class ModuleInstallBatchTest extends BrowserTestBase {
    */
   public static $modules = ['test_batch_test', 'entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests loading entities created in a batch in test_batch_test_install().
    */
diff --git a/core/tests/Drupal/FunctionalTests/Datetime/TimestampAgoFormatterTest.php b/core/tests/Drupal/FunctionalTests/Datetime/TimestampAgoFormatterTest.php
index 6b592346abcebca2d582996ff2f90af484961711..9dd96c79401e4b1f4868c1da34be7504b7e06638 100644
--- a/core/tests/Drupal/FunctionalTests/Datetime/TimestampAgoFormatterTest.php
+++ b/core/tests/Drupal/FunctionalTests/Datetime/TimestampAgoFormatterTest.php
@@ -41,6 +41,11 @@ class TimestampAgoFormatterTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php b/core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
index 064be558b0c6a651692b234817d945126b7ffc61..bf1ca56d5d877180d4f40c32fdb994bb01442ab1 100644
--- a/core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
+++ b/core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
@@ -43,6 +43,11 @@ class TimestampTest extends BrowserTestBase {
    */
   public static $modules = ['node', 'entity_test', 'field_ui'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormCorrectUserInputMappingOnFieldDeltaElementsTest.php b/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormCorrectUserInputMappingOnFieldDeltaElementsTest.php
index 6c88599d8a7528e25b333fdabaff4a90ad123e1c..3248aadaf9ab20eab02517364b98e69619adbea0 100644
--- a/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormCorrectUserInputMappingOnFieldDeltaElementsTest.php
+++ b/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormCorrectUserInputMappingOnFieldDeltaElementsTest.php
@@ -33,6 +33,11 @@ class ContentEntityFormCorrectUserInputMappingOnFieldDeltaElementsTest extends B
    */
   public static $modules = ['entity_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormFieldValidationFilteringTest.php b/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormFieldValidationFilteringTest.php
index 3daa841d7ce3869855486ddfc2869adf8ba8ebce..615175269eab2a3760a4eefe50933e8e886d369f 100644
--- a/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormFieldValidationFilteringTest.php
+++ b/core/tests/Drupal/FunctionalTests/Entity/ContentEntityFormFieldValidationFilteringTest.php
@@ -50,6 +50,11 @@ class ContentEntityFormFieldValidationFilteringTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'field_test', 'file', 'image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Entity/DeleteMultipleFormTest.php b/core/tests/Drupal/FunctionalTests/Entity/DeleteMultipleFormTest.php
index 45f88d680e26a1d85553e5046f5a7d6ec378e840..ef57bd72af354f8101bbb0dd630213eb2fa4cc4b 100644
--- a/core/tests/Drupal/FunctionalTests/Entity/DeleteMultipleFormTest.php
+++ b/core/tests/Drupal/FunctionalTests/Entity/DeleteMultipleFormTest.php
@@ -31,6 +31,11 @@ class DeleteMultipleFormTest extends BrowserTestBase {
    */
   public static $modules = ['entity_test', 'user', 'language'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/FolderTest.php b/core/tests/Drupal/FunctionalTests/FolderTest.php
index 4a66be98b567aeefc51c9e374cdcd6320e75da7e..c977672d3bf6868993a16a850fc2dca29c915ad0 100644
--- a/core/tests/Drupal/FunctionalTests/FolderTest.php
+++ b/core/tests/Drupal/FunctionalTests/FolderTest.php
@@ -20,6 +20,11 @@ class FolderTest extends BrowserTestBase {
    */
   public static $modules = ['image'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testFolderSetup() {
     $directory = 'public://styles';
     $this->assertTrue(\Drupal::service('file_system')->prepareDirectory($directory, FALSE), 'Directory created.');
diff --git a/core/tests/Drupal/FunctionalTests/GetTestMethodCallerExtendsTest.php b/core/tests/Drupal/FunctionalTests/GetTestMethodCallerExtendsTest.php
index 81ebb813cd32b3694c7acaf0c0ff71cafac4bd4a..123c22b57380c77fdc126dfda885b3a95b1c305b 100644
--- a/core/tests/Drupal/FunctionalTests/GetTestMethodCallerExtendsTest.php
+++ b/core/tests/Drupal/FunctionalTests/GetTestMethodCallerExtendsTest.php
@@ -11,6 +11,11 @@
  */
 class GetTestMethodCallerExtendsTest extends GetTestMethodCallerTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * A test method that is not present in the parent class.
    */
@@ -18,7 +23,7 @@ public function testGetTestMethodCallerChildClass() {
     $method_caller = $this->getTestMethodCaller();
     $expected = [
       'file' => __FILE__,
-      'line' => 18,
+      'line' => 23,
       'function' => __CLASS__ . '->' . __FUNCTION__ . '()',
       'class' => BrowserTestBase::class,
       'object' => $this,
diff --git a/core/tests/Drupal/FunctionalTests/GetTestMethodCallerTest.php b/core/tests/Drupal/FunctionalTests/GetTestMethodCallerTest.php
index f40ff20e921a02afab9b0e51d2a0bf4a6761b315..9baad8f27b3b889c1e9d35add1d047c00e15eaa9 100644
--- a/core/tests/Drupal/FunctionalTests/GetTestMethodCallerTest.php
+++ b/core/tests/Drupal/FunctionalTests/GetTestMethodCallerTest.php
@@ -11,6 +11,11 @@
  */
 class GetTestMethodCallerTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests BrowserTestBase::getTestMethodCaller().
    */
@@ -18,7 +23,7 @@ public function testGetTestMethodCaller() {
     $method_caller = $this->getTestMethodCaller();
     $expected = [
       'file' => __FILE__,
-      'line' => 18,
+      'line' => 23,
       'function' => __CLASS__ . '->' . __FUNCTION__ . '()',
       'class' => BrowserTestBase::class,
       'object' => $this,
diff --git a/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonAnonTest.php
index 688f26b5f43f15791e4b4d4570a18528859e24c5..254103a087a146dd364d45948d219840a04b29b5 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class BaseFieldOverrideHalJsonAnonTest extends BaseFieldOverrideResourceTestBase
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonBasicAuthTest.php
index 84907fcc5782311ec23208ba244992854afa40b6..3ebdd19b4d3e69be0172934689a2044a8eccdbcd 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class BaseFieldOverrideHalJsonBasicAuthTest extends BaseFieldOverrideResourceTes
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonCookieTest.php
index e373bd824ba0d4bbec5fca61da4c69e9b67928e9..c119372abe0cb77aa7842fbc9b7e497445493a03 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/BaseFieldOverrideHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class BaseFieldOverrideHalJsonCookieTest extends BaseFieldOverrideResourceTestBa
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonAnonTest.php
index 443b607afa5e6d2e79f22e6a399b2bf5e0ec0975..06bea1c955b1accd106ef0e463495ed010c84e56 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class DateFormatHalJsonAnonTest extends DateFormatResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonBasicAuthTest.php
index afab361f3c94e9cea5d88f69c1e25c2bd6616551..106cc68773981e511a5bcea181b7579f627ff585 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class DateFormatHalJsonBasicAuthTest extends DateFormatResourceTestBase {
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonCookieTest.php
index 2b0fbd6a2e3f4c3fb4fa220f612c93ddc6fef4ba..17e01a7f7537a19db56ceb4bc47783d84004f65a 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/DateFormatHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class DateFormatHalJsonCookieTest extends DateFormatResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonAnonTest.php
index 1729c456bd323e4e98cb7565b9f6cfe061d5e62e..726971df204c477edec102e6fb87ab2a69341eaf 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class EntityFormDisplayHalJsonAnonTest extends EntityFormDisplayResourceTestBase
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonBasicAuthTest.php
index c8adf75796ef2998d3adb4267be761ef94b8ce43..4a051751c921759cecd1bdc77d48bd0f0cb4bfcf 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class EntityFormDisplayHalJsonBasicAuthTest extends EntityFormDisplayResourceTes
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonCookieTest.php
index d519e4a8df0b47c462e0d55d4c58b4203f0a9a02..1a7aa235fef54be3d2843ebacf097925d568aea0 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityFormDisplayHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class EntityFormDisplayHalJsonCookieTest extends EntityFormDisplayResourceTestBa
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonAnonTest.php
index 85d3b6f1167bb6fcacae67c75cbbf64180ee8af5..fb729e522304cee585ea30491074d0c418252590 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class EntityFormModeHalJsonAnonTest extends EntityFormModeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonBasicAuthTest.php
index 373a13eb66f4c6c172e19380d9724d3a857df81f..7cc7e85f91c7062b1d61f9679e3f413cf7f64c88 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class EntityFormModeHalJsonBasicAuthTest extends EntityFormModeResourceTestBase
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonCookieTest.php
index 2df80e31c24a16938d25f68c2148c275adffe954..4c471c8294581ecc396a9e13cf86119941e55f55 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityFormModeHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class EntityFormModeHalJsonCookieTest extends EntityFormModeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonAnonTest.php
index ff5feaef5eb3af606ea82007b8ae22e85a4d5818..0edefde3636afd46e88a8c26710139918444d04f 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class EntityViewDisplayHalJsonAnonTest extends EntityViewDisplayResourceTestBase
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonBasicAuthTest.php
index 4ba2f444658f6dfe0fbc79c7e40a9795334c2000..841ec8e3b9d7961350a709a7788f56c0bcc43198 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityViewDisplayHalJsonBasicAuthTest extends EntityViewDisplayHalJsonAnon
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonCookieTest.php
index 9f822bf636fc2b2515c68d2bc3e925074fb44aa5..a45e86265d0613cd401a8e4729e2460c2a97e944 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityViewDisplayHalJsonCookieTest.php
@@ -16,4 +16,9 @@ class EntityViewDisplayHalJsonCookieTest extends EntityViewDisplayHalJsonAnonTes
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonAnonTest.php
index fdd5d7c46c4401c048756b3859eee9d3b06fcbce..5ec8cddab6854a144f6569fb5a37f5a30f1f0c0c 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonAnonTest.php
@@ -17,6 +17,11 @@ class EntityViewModeHalJsonAnonTest extends EntityViewModeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonBasicAuthTest.php
index e13ea25b032b9e7922f031e449c7ea43d49e0b26..5d7b1b90fddeb2f559e256e377ac28cc69c20698 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonBasicAuthTest.php
@@ -17,6 +17,11 @@ class EntityViewModeHalJsonBasicAuthTest extends EntityViewModeResourceTestBase
    */
   public static $modules = ['hal', 'basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonCookieTest.php
index b5f4ad470f7720140dc3c6b062f3078246237707..2f883089ad454742954f2acab10d26e30b7fd25f 100644
--- a/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Hal/EntityViewModeHalJsonCookieTest.php
@@ -17,6 +17,11 @@ class EntityViewModeHalJsonCookieTest extends EntityViewModeResourceTestBase {
    */
   public static $modules = ['hal'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/HttpKernel/CorsIntegrationTest.php b/core/tests/Drupal/FunctionalTests/HttpKernel/CorsIntegrationTest.php
index cc43936d6f166f27d0b63965da080cd07337983d..75ba6fc2296b0324b42e416acc05b1a92a0e9cfc 100644
--- a/core/tests/Drupal/FunctionalTests/HttpKernel/CorsIntegrationTest.php
+++ b/core/tests/Drupal/FunctionalTests/HttpKernel/CorsIntegrationTest.php
@@ -21,6 +21,11 @@ class CorsIntegrationTest extends BrowserTestBase {
    */
   public static $modules = ['system', 'test_page_test', 'page_cache'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testCrossSiteRequest() {
     // Test default parameters.
     $cors_config = $this->container->getParameter('cors.config');
diff --git a/core/tests/Drupal/FunctionalTests/Image/ToolkitSetupFormTest.php b/core/tests/Drupal/FunctionalTests/Image/ToolkitSetupFormTest.php
index d501f1d98c2c95fc7ef346604edf54ac6abaca4f..9c9720e177bbfdaa6efbea72ec79859d8ef09da5 100644
--- a/core/tests/Drupal/FunctionalTests/Image/ToolkitSetupFormTest.php
+++ b/core/tests/Drupal/FunctionalTests/Image/ToolkitSetupFormTest.php
@@ -25,6 +25,11 @@ class ToolkitSetupFormTest extends BrowserTestBase {
    */
   public static $modules = ['system', 'image_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Image/ToolkitTest.php b/core/tests/Drupal/FunctionalTests/Image/ToolkitTest.php
index 17c91158c2658e411c3ee7a9a0538f907d7065a7..e91dab4b2979ddc2ef91b7ca2d62ac35dc952929 100644
--- a/core/tests/Drupal/FunctionalTests/Image/ToolkitTest.php
+++ b/core/tests/Drupal/FunctionalTests/Image/ToolkitTest.php
@@ -9,6 +9,11 @@
  */
 class ToolkitTest extends ToolkitTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Check that ImageToolkitManager::getAvailableToolkits() only returns
    * available toolkits.
diff --git a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileExistingSettingsTest.php b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileExistingSettingsTest.php
index ee97a023f401076c86d342d4a460415246005010..d5194bdec11ec6f2510668f7b9e243757972b4cc 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileExistingSettingsTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileExistingSettingsTest.php
@@ -22,6 +22,11 @@ class DistributionProfileExistingSettingsTest extends InstallerTestBase {
    */
   protected $info;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTest.php
index dce7ef51178b73c92a814e1180394418f47db395..bb7801e7d9ea7c8eae2a065dc8966be51773345f 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTest.php
@@ -18,6 +18,11 @@ class DistributionProfileTest extends InstallerTestBase {
    */
   protected $info;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected function prepareEnvironment() {
     parent::prepareEnvironment();
     $this->info = [
diff --git a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationQueryTest.php b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationQueryTest.php
index e4a447f5e6cfefb45e9bd13f0c0de3de50e21160..0fc21f42b9ac11393a6fba4a8fe63346d0e593e8 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationQueryTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationQueryTest.php
@@ -13,6 +13,11 @@
  */
 class DistributionProfileTranslationQueryTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationTest.php b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationTest.php
index ac6697a0276a480cbc2748f453110eab09fc7f43..ec6d81146367afa0ee1a08aef19ba2a69dc887d0 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/DistributionProfileTranslationTest.php
@@ -13,6 +13,11 @@
  */
 class DistributionProfileTranslationTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesBcTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesBcTest.php
index 41526333446f8b680142a9798c4bdce10ea3fe6c..2f3890efc0141bc72267ea1a417f6aad2af9463e 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesBcTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesBcTest.php
@@ -12,6 +12,11 @@
  */
 class InstallProfileDependenciesBcTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesTest.php
index 4ceb7f8af90e9019e5e94e899ab1afa9b4c24736..1e397e069ec8ad2f022e54d5d285fb167f631b54 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallProfileDependenciesTest.php
@@ -12,6 +12,11 @@
  */
 class InstallProfileDependenciesTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryErrorTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryErrorTest.php
index 0d955b6957c566e61c5e1f5a136aa9d829c670b2..38a08bf3b8769654291a2dfd49b9b6ad51c0f263 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryErrorTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryErrorTest.php
@@ -11,6 +11,11 @@
  */
 class InstallerConfigDirectorySetNoDirectoryErrorTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The directory where the sync directory should be created during install.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryTest.php
index dcb47b5ee3406fa46a9c0bc34ddf6171e9e7a4b5..5863d931f465ef1e7c513feee34c8203a2ea4969 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerConfigDirectorySetNoDirectoryTest.php
@@ -11,6 +11,11 @@
  */
 class InstallerConfigDirectorySetNoDirectoryTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The sync directory created during the install.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerCustomConfigDirectoryCreateTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerCustomConfigDirectoryCreateTest.php
index 9e7ab31578a2cd2c86efd4924b56bea3079064c1..ee8b68e18d48b789b18fb9c0156181f03cb7d2c9 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerCustomConfigDirectoryCreateTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerCustomConfigDirectoryCreateTest.php
@@ -12,6 +12,11 @@
  */
 class InstallerCustomConfigDirectoryCreateTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerDatabaseErrorMessagesTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerDatabaseErrorMessagesTest.php
index 69c209070389721255719335813e273556fbc7da..021fbc9a221ce38cf915a5a89a8193b74d88b34d 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerDatabaseErrorMessagesTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerDatabaseErrorMessagesTest.php
@@ -11,6 +11,11 @@
  */
 class InstallerDatabaseErrorMessagesTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerEmptySettingsTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerEmptySettingsTest.php
index 839009ecfbe4ad14767ad1090748f6e56da0bae4..2f3e5acc660e063c698878742ba0e1eb458e593b 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerEmptySettingsTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerEmptySettingsTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerEmptySettingsTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigDirectoryTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigDirectoryTest.php
index ec6b72b48fc32b26ab618287c83991f7651a3935..eae925a62af25625c3e9a4d839961d73e677821b 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigDirectoryTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigDirectoryTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigDirectoryTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The expected file perms of the folder.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigMultilingualTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigMultilingualTest.php
index db05d32031e6c7f3109184217f26e489f472473b..2feb840693d7c2dbd2beb8aca2acd1bad2fbf2e8 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigMultilingualTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigMultilingualTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigMultilingualTest extends InstallerExistingConfigTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoConfigTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoConfigTest.php
index 01ddefa9048a256fd1b169583c0a8187c783b6ab..b19ee442677f7efea9871c0ec411755ffa4903ba 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoConfigTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoConfigTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigNoConfigTest extends InstallerExistingConfigTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   protected $profile = 'no_config_profile';
 
   /**
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoSystemSiteTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoSystemSiteTest.php
index 4ac68d4e8637c48883e872b796bc3ebc819de984..42d1c11f6cb08eb9da932bac6a1646482c8d86d5 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoSystemSiteTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigNoSystemSiteTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigNoSystemSiteTest extends InstallerExistingConfigTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigProfileHookInstall.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigProfileHookInstall.php
index 2d9d6cdfc121c4480fecdf4e60047033456619e5..09f377415353c05fee7e76ed5d8105137ae262e4 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigProfileHookInstall.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigProfileHookInstall.php
@@ -11,6 +11,11 @@ class InstallerExistingConfigProfileHookInstall extends InstallerExistingConfigT
 
   protected $profile = 'config_profile_with_hook_install';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryMultilingualTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryMultilingualTest.php
index e223998ed7cf6a4f934d704d65cfd7fcb8d69e67..42bf5b5fbb7006f1d061f06d464f70229606b72f 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryMultilingualTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryMultilingualTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigSyncDirectoryMultilingualTest extends InstallerExistingConfigTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryProfileHookInstall.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryProfileHookInstall.php
index 63aea303de3b66a51b077d2bab91e122e4d7ba04..38a06971fa2188acad23c75144eaf45e20ea955d 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryProfileHookInstall.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDirectoryProfileHookInstall.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigSyncDirectoryProfileHookInstall extends InstallerExistingConfigTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDriectoryProfileMismatchTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDriectoryProfileMismatchTest.php
index 54b25ee8de676ab0a672d528a88c0f770b23bf59..80b392a72a70b87feb1fb4459529019fbe6f863f 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDriectoryProfileMismatchTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigSyncDriectoryProfileMismatchTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigSyncDriectoryProfileMismatchTest extends InstallerExistingConfigTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigTest.php
index c1e75a87aeb4bc63e158e9dd44bcd1ccf3da30ae..01e71cf8561444c855f74d29d50a711fbbe20a67 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingConfigTest extends InstallerExistingConfigTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingDatabaseSettingsTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingDatabaseSettingsTest.php
index caf8b48097cea508dcd7202955a5b42956b6c741..021abd42f745743d6c7aa7dc727e037041127b79 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingDatabaseSettingsTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingDatabaseSettingsTest.php
@@ -12,6 +12,11 @@
  */
 class InstallerExistingDatabaseSettingsTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingInstallationTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingInstallationTest.php
index 7b29d4acc834127ed58695d39e9a594bcafabb74..1c8bfb9e5cec60b842f1a0d3402f6d240ce24143 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingInstallationTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingInstallationTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerExistingInstallationTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Verifies that Drupal can't be reinstalled while an existing installation is
    * available.
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsMismatchProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsMismatchProfileTest.php
index 596f522fb8426f4b9088b67d5d7b7c1e0b352af6..acbd93047e4c5cfe4d0bd468330f01b3740f0057 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsMismatchProfileTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsMismatchProfileTest.php
@@ -15,6 +15,11 @@
  */
 class InstallerExistingSettingsMismatchProfileTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsNoProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsNoProfileTest.php
index 791135e7a0b1075de5f84e53d9bbdbc160264f0e..42f3542212059a37539ef038cb9fb28f36801287 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsNoProfileTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsNoProfileTest.php
@@ -13,6 +13,11 @@
  */
 class InstallerExistingSettingsNoProfileTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsReadOnlyMismatchProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsReadOnlyMismatchProfileTest.php
index 46d6f8b94714be7086c760abfedc498e5de50d22..86ac0a5956f848ab097b853338629282dc49768f 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsReadOnlyMismatchProfileTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsReadOnlyMismatchProfileTest.php
@@ -15,6 +15,11 @@
  */
 class InstallerExistingSettingsReadOnlyMismatchProfileTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsTest.php
index 5af025e5ee4c668198e40d35d3862f17809bcb5c..f5fb5dc225e4bcfe058699692acd8c396119e712 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerExistingSettingsTest.php
@@ -13,6 +13,11 @@
  */
 class InstallerExistingSettingsTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguageDirectionTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguageDirectionTest.php
index ac2c46297f046c58f5a1f22b83d406d5fdb658b9..48d50af4d1e8a93186f082e25658a4d61f6e830a 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguageDirectionTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguageDirectionTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerLanguageDirectionTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Overrides the language code the installer should use.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguagePageTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguagePageTest.php
index 5ea9692f341bd415f6c6e80a5a997dc64121d47f..692dd314b1cbd3972ffd3df3312795537740693a 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguagePageTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerLanguagePageTest.php
@@ -11,6 +11,11 @@
  */
 class InstallerLanguagePageTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Installer step: Select language.
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerNonEnglishProfileWithoutLocaleModuleTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerNonEnglishProfileWithoutLocaleModuleTest.php
index 1ae12c7115a807b7bdafdede85a6ef0283a58157..ecfe255b94040147d967961221f9eef7e7cb71dc 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerNonEnglishProfileWithoutLocaleModuleTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerNonEnglishProfileWithoutLocaleModuleTest.php
@@ -11,6 +11,11 @@
  */
 class InstallerNonEnglishProfileWithoutLocaleModuleTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The testing profile name.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerProfileRequirementsTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerProfileRequirementsTest.php
index 56e7e245370bf6c208b74aa187f8e5c1f090f995..1dd1649e3ec7ac6491359e47bbf2117b6f2d9ea8 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerProfileRequirementsTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerProfileRequirementsTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerProfileRequirementsTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerSiteConfigProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerSiteConfigProfileTest.php
index 791befd0468b6795ad7f7bc00b375ec9c7c95b0d..a0483aba0190c2df7171e984c1b23146c9dfda1b 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerSiteConfigProfileTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerSiteConfigProfileTest.php
@@ -10,6 +10,11 @@
  */
 class InstallerSiteConfigProfileTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php
index 5a09571b3993313bc88830f9928ae831105dfc9c..f282de86785a7b6396a55162207aa566dda83c19 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerSkipPermissionHardeningTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerSkipPermissionHardeningTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php
index 97d59d055376c95cdd90d60b7d24a16ed23209eb..1fd54494825344c609649101870ae5d8f450bf67 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensures that the user page is available after installation.
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageForeignTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageForeignTest.php
index 58100cdbf3d73b7fade0272496b7d6e715423ed6..846aa212ffaaa2511b6e859c5143a57097ef7f16 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageForeignTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageForeignTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerTranslationMultipleLanguageForeignTest extends InstallerTranslationMultipleLanguageTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Overrides the language code in which to install Drupal.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageKeepEnglishTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageKeepEnglishTest.php
index 3c103103a31ebc4d90b1e90e65a7e88bff2edd56..5ff0f7521d739b411d7a8ee3999b050b8aec7e99 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageKeepEnglishTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageKeepEnglishTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerTranslationMultipleLanguageKeepEnglishTest extends InstallerTranslationMultipleLanguageForeignTest {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Switch to the multilingual testing profile with English kept.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageTest.php
index dcd112ae19bcf54747b1985af727c35e5b1669f0..0f06d17a5cf3deb0080bd17e89993f4cada74c73 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationMultipleLanguageTest.php
@@ -9,6 +9,11 @@
  */
 class InstallerTranslationMultipleLanguageTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Switch to the multilingual testing profile.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationQueryTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationQueryTest.php
index 152713b273256a3d03eddbad82de4910e31bbc8a..5c1c14a989612070a712785be82a542d5555109d 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationQueryTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationQueryTest.php
@@ -11,6 +11,11 @@
  */
 class InstallerTranslationQueryTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Overrides the language code in which to install Drupal.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationTest.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationTest.php
index 55ce6b534c7c75bbd70e7b887580c52f187da271..c38d4719fc8942e4d992f101be246d511a158824 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTranslationTest.php
@@ -12,6 +12,11 @@
  */
 class InstallerTranslationTest extends InstallerTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'classy';
+
   /**
    * Overrides the language code in which to install Drupal.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/MinimalInstallerTest.php b/core/tests/Drupal/FunctionalTests/Installer/MinimalInstallerTest.php
index baefe0fe1c6f1f27275770ab64262d9178efcc0a..4ff32ec9d07fc1cd7afd7d2885cf166743b76af6 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/MinimalInstallerTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/MinimalInstallerTest.php
@@ -18,6 +18,11 @@ class MinimalInstallerTest extends ConfigAfterInstallerTestBase {
    */
   protected $profile = 'minimal';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensures that the exported minimal configuration is up to date.
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/MultipleDistributionsProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/MultipleDistributionsProfileTest.php
index 4ced7a704e5134bd832bb80eeec6fc66cbc67687..a0f2069cba56f24872be136af8fa701b896ec171 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/MultipleDistributionsProfileTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/MultipleDistributionsProfileTest.php
@@ -18,6 +18,11 @@ class MultipleDistributionsProfileTest extends InstallerTestBase {
    */
   protected $info;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/SingleVisibleProfileTest.php b/core/tests/Drupal/FunctionalTests/Installer/SingleVisibleProfileTest.php
index a6366ee76079a8ba111ba551e6832a2f915cab0a..02e60a817e7a6b0f3dbb4b4de66516bbb7b69f5e 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/SingleVisibleProfileTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/SingleVisibleProfileTest.php
@@ -20,6 +20,11 @@ class SingleVisibleProfileTest extends InstallerTestBase {
    */
   protected $profile = NULL;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/SiteNameTest.php b/core/tests/Drupal/FunctionalTests/Installer/SiteNameTest.php
index b77fe35a725a573e0d2ce5d6f32684676efe6a45..44087f2004e871f8f0211b856dfd40cae1949574 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/SiteNameTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/SiteNameTest.php
@@ -18,6 +18,11 @@ class SiteNameTest extends BrowserTestBase {
    */
   protected $siteName;
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Installer/TestingProfileInstallTest.php b/core/tests/Drupal/FunctionalTests/Installer/TestingProfileInstallTest.php
index d18de97d566789ccf3e07fe943b318f357a5a381..b358787ba98d5f20313718bb91c3d335fc0af39b 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/TestingProfileInstallTest.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/TestingProfileInstallTest.php
@@ -16,6 +16,11 @@ class TestingProfileInstallTest extends BrowserTestBase {
    */
   protected $profile = 'testing';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Ensure the Update module and its dependencies are installed.
    */
diff --git a/core/tests/Drupal/FunctionalTests/MailCaptureTest.php b/core/tests/Drupal/FunctionalTests/MailCaptureTest.php
index 0f48d79e0e041d9edeed5dcd6e281ac935b313a5..74e2f07ef8c1441ccf70754c8505990aece78d94 100644
--- a/core/tests/Drupal/FunctionalTests/MailCaptureTest.php
+++ b/core/tests/Drupal/FunctionalTests/MailCaptureTest.php
@@ -17,6 +17,11 @@ class MailCaptureTest extends BrowserTestBase {
     getMails as drupalGetMails;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Test to see if the wrapper function is executed correctly.
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonAnonTest.php
index d5a416ad85e69d01e3ba45d1711eee51625cc463..6e75e823763a60493fa73f28d9fba0b04eb84405 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonAnonTest.php
@@ -21,4 +21,9 @@ class BaseFieldOverrideJsonAnonTest extends BaseFieldOverrideResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonBasicAuthTest.php
index c40de5517b3c4435b8ab5c5d5ff201df74fd7d3b..c922c8d6d1a64c0cee8d52ae8fa0708159788e2d 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class BaseFieldOverrideJsonBasicAuthTest extends BaseFieldOverrideResourceTestBa
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonCookieTest.php
index a60fdf493682a167e454bcfcad34b7c39f524553..142cc6cb095c1738367a64c87a89ee1faa67220b 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideJsonCookieTest.php
@@ -26,4 +26,9 @@ class BaseFieldOverrideJsonCookieTest extends BaseFieldOverrideResourceTestBase
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlAnonTest.php
index 7b995b425045d4c649db24de678daeaa31aa6da3..887c53fd42f68df4656e0fdc791f57b87a3de7a2 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlAnonTest.php
@@ -23,4 +23,9 @@ class BaseFieldOverrideXmlAnonTest extends BaseFieldOverrideResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlBasicAuthTest.php
index 1e3f833567418e3ade3dbfa59fd947ead307b612..3a3f08bf5719c54b99cc280a44e5691381b15b1e 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlBasicAuthTest.php
@@ -28,6 +28,11 @@ class BaseFieldOverrideXmlBasicAuthTest extends BaseFieldOverrideResourceTestBas
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlCookieTest.php
index ba1d166c826c39563496a7700e5d863379e0c309..0aed06ffcb7f7a86bc379ee9e4ca18b311522003 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/BaseFieldOverrideXmlCookieTest.php
@@ -28,4 +28,9 @@ class BaseFieldOverrideXmlCookieTest extends BaseFieldOverrideResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonAnonTest.php
index ad53e9da2f2fcd3dad5e2a394bf40097a39026c4..a114aa609a937155ad5bfc7eae0e6e89f18b8908 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonAnonTest.php
@@ -21,4 +21,9 @@ class DateFormatJsonAnonTest extends DateFormatResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonBasicAuthTest.php
index 453f8a19203512d376a517d283df9476b43d6bb7..0ae83504a45f6f396407c800a4e92682956dedce 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonBasicAuthTest.php
@@ -26,6 +26,11 @@ class DateFormatJsonBasicAuthTest extends DateFormatResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonCookieTest.php
index 2c1548f32dbf5e999cc154e0564414fc8054db4a..61e1ccaee5fef0f291cf8edc0e494e510a4b76fe 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/DateFormatJsonCookieTest.php
@@ -26,4 +26,9 @@ class DateFormatJsonCookieTest extends DateFormatResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlAnonTest.php
index 8eec7d4e8c00f66ed77c1bcf863ee7ca11e25200..47ea72b28f0088b0073799728547e1d193441f4d 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlAnonTest.php
@@ -23,4 +23,9 @@ class DateFormatXmlAnonTest extends DateFormatResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlBasicAuthTest.php
index eb787a99b83c9c39b8d8d64f96e4ca47be33219c..8a09a33a8422d15a8b1f91cfc68c215d095227e2 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class DateFormatXmlBasicAuthTest extends DateFormatResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlCookieTest.php
index 124614d27d2516a9065dfe3ec177cf2258cfd8b9..7fd076fda7c9c7dba982d15237e0a8a9146d1d2d 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/DateFormatXmlCookieTest.php
@@ -28,4 +28,9 @@ class DateFormatXmlCookieTest extends DateFormatResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonAnonTest.php
index 9ae38d80d17d09d38b8772f05cc48e35abf1f62a..b39205e65c5d2e11138de0f3fb1e6f1eb48e0983 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonAnonTest.php
@@ -21,4 +21,9 @@ class EntityFormDisplayJsonAnonTest extends EntityFormDisplayResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonBasicAuthTest.php
index 36ca913eddaec60d93c6e45b08243512564e5986..a3871c8455992e6c183e84133ace483543090b2b 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonBasicAuthTest.php
@@ -26,6 +26,11 @@ class EntityFormDisplayJsonBasicAuthTest extends EntityFormDisplayResourceTestBa
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonCookieTest.php
index 5154ababbaed2cb3c891c2e8c80dba851b19856b..1fdebc9f81f211afda2ce0b0233b9bf227b99bae 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayJsonCookieTest.php
@@ -26,4 +26,9 @@ class EntityFormDisplayJsonCookieTest extends EntityFormDisplayResourceTestBase
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlAnonTest.php
index da1437ed123c9bfa3c1abc57b2cda22b342e5cc2..56375974cc33af994644b9baeab90dda37ad071f 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlAnonTest.php
@@ -23,4 +23,9 @@ class EntityFormDisplayXmlAnonTest extends EntityFormDisplayResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlBasicAuthTest.php
index 2edf2460a9a569e36064020cc1c54149935b6f4e..ba89d79e1f4521f2107c6c1b72696c8eb346e420 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlBasicAuthTest.php
@@ -28,6 +28,11 @@ class EntityFormDisplayXmlBasicAuthTest extends EntityFormDisplayResourceTestBas
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlCookieTest.php
index e9e93b0d475ed99a4a4b6e83302359a3602c44e5..391370ec84056d14d7073d34e639ecf4f519c58a 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormDisplayXmlCookieTest.php
@@ -28,4 +28,9 @@ class EntityFormDisplayXmlCookieTest extends EntityFormDisplayResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonAnonTest.php
index a1cea00f1f13856d41815dcdc9ef6c1361e6c6ce..816e1e9af9edc6f07b2c630f946569187e242931 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonAnonTest.php
@@ -21,4 +21,9 @@ class EntityFormModeJsonAnonTest extends EntityFormModeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonBasicAuthTest.php
index bbfb6fbc98ef7f8d9a660739d421170c2c72f700..a813e1a2de36c7d4127e77c9af8c023b86a06f65 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonBasicAuthTest.php
@@ -26,6 +26,11 @@ class EntityFormModeJsonBasicAuthTest extends EntityFormModeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonCookieTest.php
index 5f336260e0eddc0ba442bfa94719d3bffa27bdea..f8a1753a8777b02871490533598a53cec5691e98 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeJsonCookieTest.php
@@ -26,4 +26,9 @@ class EntityFormModeJsonCookieTest extends EntityFormModeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlAnonTest.php
index 2da724f804a35b80c8918b819e57f6cf1e5f3ae9..f5065283cc32eb4d7e5fd3a72e6795d8a7bb13fc 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlAnonTest.php
@@ -23,4 +23,9 @@ class EntityFormModeXmlAnonTest extends EntityFormModeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlBasicAuthTest.php
index 721ded8fd9595c13679fb3f4cc20a791343e478f..64ce5a08311f3e8418ea08c3120baafe09a1f220 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class EntityFormModeXmlBasicAuthTest extends EntityFormModeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlCookieTest.php
index 6f426570a5645979812697870275f472854f31e8..c02d46d58bfc01d496ee1427661898624fc4eb3e 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityFormModeXmlCookieTest.php
@@ -28,4 +28,9 @@ class EntityFormModeXmlCookieTest extends EntityFormModeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonAnonTest.php
index c26362aa748c2fc64509b3c7932bd9676a6aecb0..38b1c21f7a147400ec08cee58507b42f6ff92e8b 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonAnonTest.php
@@ -21,4 +21,9 @@ class EntityViewDisplayJsonAnonTest extends EntityViewDisplayResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonBasicAuthTest.php
index f4f2d15045c11cef4893671162f2c8c6e723573c..efd558c9f6f8083165387f26feaad8e647d25234 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityViewDisplayJsonBasicAuthTest extends EntityViewDisplayResourceTestBa
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonCookieTest.php
index 6f58323426443df7a29b3086ca24e4c435ae46e0..90ef3a05bc4a93c07c74d674e5b572039ba2d5b6 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayJsonCookieTest.php
@@ -26,4 +26,9 @@ class EntityViewDisplayJsonCookieTest extends EntityViewDisplayResourceTestBase
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlAnonTest.php
index 561f2374fd42e46ff94868ede9d636b24d5dff75..1ae34e3e8d9be0667f2d915f9f96c080571383ed 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlAnonTest.php
@@ -23,4 +23,9 @@ class EntityViewDisplayXmlAnonTest extends EntityViewDisplayResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlBasicAuthTest.php
index 7c7ce5bb03ab07b029e5c340f9c6b934a3c2dc94..be597c534ce52f067e2c575cc4371fc19d40b50e 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class EntityViewDisplayXmlBasicAuthTest extends EntityViewDisplayResourceTestBas
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlCookieTest.php
index 9024ff71aedb18225e5268fbe8edb45f198e1daf..e3f688a670f42d88258d4ca44107d20dba931dc3 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewDisplayXmlCookieTest.php
@@ -28,4 +28,9 @@ class EntityViewDisplayXmlCookieTest extends EntityViewDisplayResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonAnonTest.php
index 79d7e7740f1cabe30288bab1961c6fefeeaae5b6..6d65359c916b15134edaaa2d656504a27503620e 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonAnonTest.php
@@ -21,4 +21,9 @@ class EntityViewModeJsonAnonTest extends EntityViewModeResourceTestBase {
    */
   protected static $mimeType = 'application/json';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonBasicAuthTest.php
index e34a58c660eb8c2ee5a320c384fe93c4c88f5408..70f5271ea5fd491304a1b87afd266bd3bc4bb922 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonBasicAuthTest.php
@@ -16,6 +16,11 @@ class EntityViewModeJsonBasicAuthTest extends EntityViewModeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonCookieTest.php
index 5a8ac6d190a395e3a3d4be68df00b814125128cb..9c8cb402433e76771ea528ba5bb2626a5bc181a4 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeJsonCookieTest.php
@@ -26,4 +26,9 @@ class EntityViewModeJsonCookieTest extends EntityViewModeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlAnonTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlAnonTest.php
index 6e359484172d806b46b8261cd8c41af437a9c7b7..a518ea3c4767d34d40fe6df8ecbfa17ab3c60baf 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlAnonTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlAnonTest.php
@@ -23,4 +23,9 @@ class EntityViewModeXmlAnonTest extends EntityViewModeResourceTestBase {
    */
   protected static $mimeType = 'text/xml; charset=UTF-8';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlBasicAuthTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlBasicAuthTest.php
index 1b1e7181d0ad36ea18e2d6ab5f9956dbfa33157f..510ef4dea7b7d3cfd38352f3b6f5a79c7d136b93 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlBasicAuthTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlBasicAuthTest.php
@@ -18,6 +18,11 @@ class EntityViewModeXmlBasicAuthTest extends EntityViewModeResourceTestBase {
    */
   public static $modules = ['basic_auth'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlCookieTest.php b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlCookieTest.php
index bde3e24664cbd4bddc0e3565a2a1cc28a022f815..88df86e5cdcbe5b1c74a906fd2dc4bb74421bede 100644
--- a/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlCookieTest.php
+++ b/core/tests/Drupal/FunctionalTests/Rest/EntityViewModeXmlCookieTest.php
@@ -28,4 +28,9 @@ class EntityViewModeXmlCookieTest extends EntityViewModeResourceTestBase {
    */
   protected static $auth = 'cookie';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
 }
diff --git a/core/tests/Drupal/FunctionalTests/Routing/CaseInsensitivePathTest.php b/core/tests/Drupal/FunctionalTests/Routing/CaseInsensitivePathTest.php
index 96b59d7be00a45acdbc33c5d6445fc90c1686737..a5532b24ad13da55be3573c8b28c0fa6554c6a40 100644
--- a/core/tests/Drupal/FunctionalTests/Routing/CaseInsensitivePathTest.php
+++ b/core/tests/Drupal/FunctionalTests/Routing/CaseInsensitivePathTest.php
@@ -16,6 +16,11 @@ class CaseInsensitivePathTest extends BrowserTestBase {
    */
   public static $modules = ['system', 'views', 'node', 'system_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/tests/Drupal/FunctionalTests/Routing/DefaultFormatTest.php b/core/tests/Drupal/FunctionalTests/Routing/DefaultFormatTest.php
index 26296485e3783cbe38a290aeac8448eff44bfe24..6a6f63f33ca88042cf72bc5c24374e67ad95b2ea 100644
--- a/core/tests/Drupal/FunctionalTests/Routing/DefaultFormatTest.php
+++ b/core/tests/Drupal/FunctionalTests/Routing/DefaultFormatTest.php
@@ -14,6 +14,11 @@ class DefaultFormatTest extends BrowserTestBase {
    */
   public static $modules = ['system', 'default_format_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testFoo() {
     $this->drupalGet('/default_format_test/human');
     $this->assertSame('format:html', $this->getSession()->getPage()->getContent());
diff --git a/core/tests/Drupal/FunctionalTests/Routing/LazyRouteProviderInstallTest.php b/core/tests/Drupal/FunctionalTests/Routing/LazyRouteProviderInstallTest.php
index cec35a07acc0b7627795ea1f7853f6128461e70f..d0d9be35677e2a805615e422d3dd3be21916111e 100644
--- a/core/tests/Drupal/FunctionalTests/Routing/LazyRouteProviderInstallTest.php
+++ b/core/tests/Drupal/FunctionalTests/Routing/LazyRouteProviderInstallTest.php
@@ -14,6 +14,11 @@ class LazyRouteProviderInstallTest extends BrowserTestBase {
    */
   protected static $modules = ['lazy_route_provider_install_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests that the lazy route provider is used during a module install.
    */
diff --git a/core/tests/Drupal/FunctionalTests/Routing/PathEncodedTest.php b/core/tests/Drupal/FunctionalTests/Routing/PathEncodedTest.php
index bf33b18f309061779e9dd83009a66888f4ec6b25..9962b993890e86baf18ff9a7bad371040200237c 100644
--- a/core/tests/Drupal/FunctionalTests/Routing/PathEncodedTest.php
+++ b/core/tests/Drupal/FunctionalTests/Routing/PathEncodedTest.php
@@ -21,6 +21,11 @@ class PathEncodedTest extends BrowserTestBase {
    */
   public static $modules = ['system', 'path_encoded_test'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   public function testGetEncoded() {
     $route_paths = [
       'path_encoded_test.colon' => '/hi/llamma:party',
diff --git a/core/tests/Drupal/FunctionalTests/Routing/RouteCachingLanguageTest.php b/core/tests/Drupal/FunctionalTests/Routing/RouteCachingLanguageTest.php
index ba4ec2bea2c38dced4aca764fc9825932b497ce8..27eab11dc78b04a0c6c632c35d08ecbe8995366a 100644
--- a/core/tests/Drupal/FunctionalTests/Routing/RouteCachingLanguageTest.php
+++ b/core/tests/Drupal/FunctionalTests/Routing/RouteCachingLanguageTest.php
@@ -22,6 +22,11 @@ class RouteCachingLanguageTest extends BrowserTestBase {
    */
   public static $modules = ['path', 'node', 'content_translation', 'link', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * An user with permissions to administer content types.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Routing/RouteCachingNonPathLanguageNegotiationTest.php b/core/tests/Drupal/FunctionalTests/Routing/RouteCachingNonPathLanguageNegotiationTest.php
index 37a07c69fe563dee454f0095e552ae26b50e435e..43e5845306b42d2f90a02958ea2e8d08ed977831 100644
--- a/core/tests/Drupal/FunctionalTests/Routing/RouteCachingNonPathLanguageNegotiationTest.php
+++ b/core/tests/Drupal/FunctionalTests/Routing/RouteCachingNonPathLanguageNegotiationTest.php
@@ -23,6 +23,11 @@ class RouteCachingNonPathLanguageNegotiationTest extends BrowserTestBase {
    */
   public static $modules = ['language', 'block'];
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * The admin user.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Theme/BartikTest.php b/core/tests/Drupal/FunctionalTests/Theme/BartikTest.php
index 8ef9db422999b2aaf1410ada24772d1c295a8391..20b2a5da81d199488df55b4291be1f6ab531c277 100644
--- a/core/tests/Drupal/FunctionalTests/Theme/BartikTest.php
+++ b/core/tests/Drupal/FunctionalTests/Theme/BartikTest.php
@@ -14,15 +14,7 @@ class BartikTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  public function setUp() {
-    parent::setUp();
-
-    $this->assertTrue($this->container->get('theme_installer')->install(['bartik']));
-    $this->container->get('config.factory')
-      ->getEditable('system.theme')
-      ->set('default', 'bartik')
-      ->save();
-  }
+  protected $defaultTheme = 'bartik';
 
   /**
    * Tests that the Bartik theme always adds its message CSS and Classy's.
diff --git a/core/tests/Drupal/FunctionalTests/Theme/ClaroTest.php b/core/tests/Drupal/FunctionalTests/Theme/ClaroTest.php
index ad052c5c4150866e166a4e7aa034988110325dd6..a9f1d7b716e1feed686837d6d986addd79a96de5 100644
--- a/core/tests/Drupal/FunctionalTests/Theme/ClaroTest.php
+++ b/core/tests/Drupal/FunctionalTests/Theme/ClaroTest.php
@@ -25,15 +25,7 @@ class ClaroTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  public function setUp() {
-    parent::setUp();
-
-    $this->assertTrue(\Drupal::service('theme_installer')->install(['claro']));
-    $this->container->get('config.factory')
-      ->getEditable('system.theme')
-      ->set('default', 'claro')
-      ->save();
-  }
+  protected $defaultTheme = 'claro';
 
   /**
    * Tests that the Claro theme always adds its elements.css.
diff --git a/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php b/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php
index dca624e4e689391afda84922e6e6edabf233d3b7..9aabc6167180d093954165b4865832aaa0d37bd6 100644
--- a/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php
+++ b/core/tests/Drupal/FunctionalTests/Theme/ClassyTest.php
@@ -14,15 +14,7 @@ class ClassyTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  public function setUp() {
-    parent::setUp();
-
-    $this->assertTrue($this->container->get('theme_installer')->install(['classy']));
-    $this->container->get('config.factory')
-      ->getEditable('system.theme')
-      ->set('default', 'classy')
-      ->save();
-  }
+  protected $defaultTheme = 'classy';
 
   /**
    * Tests that the Classy theme always adds its message CSS.
diff --git a/core/tests/Drupal/FunctionalTests/UserHelpersTest.php b/core/tests/Drupal/FunctionalTests/UserHelpersTest.php
index 074f11e3f19b0609ae6f0cea478b6ffe0fcc41b0..ad053e362a21b2c74cdf876eb69758f1efe1f7e1 100644
--- a/core/tests/Drupal/FunctionalTests/UserHelpersTest.php
+++ b/core/tests/Drupal/FunctionalTests/UserHelpersTest.php
@@ -11,6 +11,11 @@
  */
 class UserHelpersTest extends BrowserTestBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
   /**
    * Tests WebTestBase::drupalUserIsLoggedIn().
    */
diff --git a/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php b/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
index de82e658397430f8e645c13d177f8da388a79f4d..05ec56c595983ca8c5211d57dbc6938549ba8988 100644
--- a/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
+++ b/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
@@ -187,8 +187,6 @@ public static function getSkippedDeprecations() {
       'Using the "Symfony\Component\Validator\Constraints\Length" constraint with the "min" option without setting the "allowEmptyString" one is deprecated and defaults to true. In 5.0, it will become optional and default to false.',
       'The "core/jquery.ui.checkboxradio" asset library is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. See https://www.drupal.org/node/3067969',
       'The "core/jquery.ui.controlgroup" asset library is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. See https://www.drupal.org/node/3067969',
-      // @todo Remove in https://www.drupal.org/project/drupal/issues/3082655
-      'Drupal\Tests\BrowserTestBase::$defaultTheme is required in drupal:9.0.0 when using an install profile that does not set a default theme. See https://www.drupal.org/node/2352949, which includes recommendations on which theme to use.',
       // The following deprecation is listed for Twig 2 compatibility when unit
       // testing using \Symfony\Component\ErrorHandler\DebugClassLoader.
       'The "Twig\Environment::getTemplateClass()" method is considered internal. It may change without further notice. You should not extend it from "Drupal\Core\Template\TwigEnvironment".',