diff --git a/core/themes/seven/css/theme/ckeditor-dialog.css b/core/themes/seven/css/theme/ckeditor-dialog.css
new file mode 100644
index 0000000000000000000000000000000000000000..f3d2d86a7c364044bc22714b1f80e5096e2e545c
--- /dev/null
+++ b/core/themes/seven/css/theme/ckeditor-dialog.css
@@ -0,0 +1,254 @@
+/**
+ * @file
+ * CKEditor-native dialogs theming.
+ */
+
+.cke_dialog_background_cover {
+  display: none;
+}
+.cke_dialog:before {
+  content: '';
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  background: #000;
+  opacity: 0.70;
+}
+[dir="rtl"] .cke_reset_all * {
+  text-align: right;
+  direction: rtl;
+}
+.cke_reset_all .cke_dialog_body {
+  position: relative;
+  border: 0;
+  border-radius: 0;
+  background: none;
+}
+.cke_reset_all .cke_dialog_body * {
+  font: 13px/1.538em "Lucida Grande", "Lucida Sans Unicode", "DejaVu Sans", "Lucida Sans", sans-serif;
+}
+
+/* Dialog's header. */
+.cke_reset_all .cke_dialog_title {
+  padding: 15px 49px 15px 15px;
+  border: 0;
+  border-top-left-radius: 5px;
+  border-top-right-radius: 5px;
+  font-size: 1.3344em;
+  line-height: 1.315em;
+  font-weight: 600;
+  background: #6b6b6b;
+  color: #fff;
+  box-shadow: none;
+  text-shadow: none;
+  -webkit-font-smoothing: antialiased;
+}
+[dir="rtl"] .cke_reset_all .cke_dialog_title {
+  padding: 15px 15px 15px 49px;
+}
+
+/* More specificity to prevent overriding in high density screens. */
+.cke_reset_all .cke_dialog .cke_dialog_close_button {
+  top: 16px;
+  right: 20px;
+  width: 16px;
+  height: 16px;
+  background: url(../../../../misc/icons/ffffff/ex.svg) 0 0 no-repeat;
+  opacity: 1;
+}
+[dir="rtl"] .cke_reset_all .cke_dialog .cke_dialog_close_button {
+  left: 20px;
+  right: auto;
+}
+.cke_reset_all .cke_dialog .cke_label {
+  display: none;
+}
+
+/* Dialog's body. */
+.cke_reset_all .cke_dialog_contents {
+  border-bottom-left-radius: 5px;
+  border-bottom-right-radius: 5px;
+}
+.cke_reset_all .cke_dialog_contents_body {
+  padding: 1em;
+}
+.cke_reset_all tr:hover,
+.cke_reset_all tr:focus {
+  background: none;
+}
+[dir="rtl"] .cke_reset_all .cke_dialog_ui_hbox_first,
+[dir="rtl"] .cke_reset_all .cke_dialog_ui_hbox_child {
+  padding-left: 10px;
+  padding-right: 0;
+}
+.cke_reset_all .cke_dialog_body label {
+  display: table;
+  margin: 0 0 0.1em;
+  padding: 0;
+  font-weight: bold;
+}
+.cke_reset_all .cke_dialog_body .cke_dialog_ui_input_text,
+.cke_reset_all .cke_dialog_body .cke_dialog_ui_input_textarea,
+.cke_reset_all .cke_dialog_body div.cke_dialog_ui_input_select {
+  border: 0;
+}
+.cke_reset_all .cke_dialog_body textarea,
+.cke_reset_all .cke_dialog_body input[type="text"],
+.cke_reset_all select.cke_dialog_ui_input_select {
+  box-sizing: border-box;
+  max-width: 100%;
+  margin: 0 0 3px;
+  padding: 0.3em 0.4em 0.3em 0.5em;
+  border: 1px solid #b8b8b8;
+  border-top-color: #999;
+  border-radius: 2px;
+  font-size: 1em;
+  line-height: normal;
+  background: #fcfcfa;
+  color: #595959;
+  box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.125);
+  -webkit-transition: border linear 0.2s, box-shadow linear 0.2s;
+  transition: border linear 0.2s, box-shadow linear 0.2s;
+}
+.cke_reset_all select.cke_dialog_ui_input_select {
+  padding-right: 1.5em;
+  background: #fcfcfa url(../../../../misc/icons/333333/caret-down.svg) no-repeat 99% 63%;
+}
+.cke_reset_all .cke_dialog_body textarea:focus,
+.cke_reset_all .cke_dialog_body input[type="text"]:focus,
+.cke_reset_all select.cke_dialog_ui_input_select:focus {
+  border-color: #40b6ff;
+  outline: 0;
+  box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.05), 0 0 8px #40b6ff;
+  background-color: #fff;
+}
+
+/* Dialog's footer. */
+.cke_reset_all .cke_dialog .cke_dialog_footer {
+  margin: 0;
+  padding: 15px 20px;
+  border: 0;
+  border-bottom-left-radius: 5px;
+  border-bottom-right-radius: 5px;
+  outline: none;
+  text-align: left;
+  background: #f5f5f2;
+}
+[dir="rtl"] .cke_reset_all .cke_dialog .cke_dialog_footer {
+  text-align: right;
+}
+.cke_reset_all .cke_resizer {
+  display: none;
+}
+.cke_reset_all .cke_dialog_footer_buttons {
+  margin: 0;
+}
+.cke_dialog_footer_buttons td {
+  float: right;
+}
+[dir="rtl"] .cke_dialog_footer_buttons td {
+  float: left;
+}
+.cke_reset_all a.cke_dialog_ui_button {
+  position: relative;
+  box-sizing: border-box;
+  display: inline-block;
+  margin-right: 1em;
+  padding: 4px 1.5em;
+  border: 1px solid #a6a6a6;
+  border-radius: 20em;
+  text-align: center;
+  font-weight: 600;
+  font-size: 14px;
+  font-size: 0.875rem;
+  line-height: normal;
+  background-color: #f2f1eb;
+  background-image: -webkit-linear-gradient(top, #f6f6f3, #e7e7df);
+  background-image: linear-gradient(to bottom, #f6f6f3, #e7e7df);
+  color: #333;
+  text-decoration: none;
+  text-shadow: 0 1px hsla(0, 0%, 100%, 0.6);
+  cursor: pointer;
+  -webkit-appearance: none;
+  -moz-appearance: none;
+  -webkit-transition: all 0.1s;
+  transition: all 0.1s;
+  -webkit-font-smoothing: antialiased;
+}
+[dir="rtl"] .cke_reset_all a.cke_dialog_ui_button {
+  margin-left: 1em;
+  margin-right: 0;
+}
+
+/* More specificity to prevent overriding in high contrast mode. */
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button:hover,
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button:focus {
+  padding: 4px 1.5em;
+  border: 1px solid #a6a6a6;
+  background-color: #f9f8f6;
+  background-image: -webkit-linear-gradient(top, #fcfcfa, #e9e9dd);
+  background-image: linear-gradient(to bottom, #fcfcfa, #e9e9dd);
+  color: #1a1a1a;
+  text-decoration: none;
+  box-shadow: 0 1px 2px hsla(0, 0%, 0%, 0.125)
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button:focus {
+  z-index: 10;
+  border: 1px solid #3AB2FF;
+  box-shadow: 0 0 0.5em 0.1em hsla(203, 100%, 60%, 0.7);
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button:active {
+  padding: 4px 1.5em;
+  border: 1px solid #a6a6a6;
+  background-color: #dfdfd9;
+  background-image: -webkit-linear-gradient(top, #f6f6f3, #e7e7df);
+  background-image: linear-gradient(to bottom, #f6f6f3, #e7e7df);
+  box-shadow: inset 0 1px 3px hsla(0, 0%, 0%, 0.2);
+  -webkit-transition: none;
+  transition: none;
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button span {
+  padding: 0;
+  font-size: 0.875rem;
+  line-height: normal;
+  text-shadow: 0 1px hsla(0, 0%, 100%, 0.6);
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button:hover span,
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button:focus span,
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button:active span {
+  padding: 0;
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button_ok {
+  border-color: #1e5c90;
+  font-weight: 700;
+  background-color: #0071b8;
+  background-image: -webkit-linear-gradient(top, #007bc6, #0071b8);
+  background-image: linear-gradient(to bottom, #007bc6, #0071b8);
+  color: #fff;
+  text-shadow: 0 1px hsla(0, 0%, 0%, 0.5);
+  -webkit-font-smoothing: antialiased;
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button_ok:hover,
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button_ok:focus {
+  background-color: #2369a6;
+  background-image: -webkit-linear-gradient(top, #0c97ed, #1f86c7);
+  background-image: linear-gradient(to bottom, #0c97ed, #1f86c7);
+  border-color: #1e5c90;
+  color: #fff;
+  box-shadow: 0 1px 2px hsla(203, 10%, 10%, 0.25);
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button_ok:focus {
+  border: 1px solid #1280df;
+  box-shadow: 0 0 0.5em 0.1em hsla(203, 100%, 60%, 0.7);
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button_ok:active {
+  background-image: -webkit-linear-gradient(top, #08639b, #0071b8);
+  background-image: linear-gradient(to bottom, #08639b, #0071b8);
+  border-color: #144b78;
+  box-shadow: inset 0 1px 3px hsla(0, 0%, 0%, 0.2);
+}
+.cke_reset_all .cke_dialog_footer_buttons a.cke_dialog_ui_button_ok span {
+  text-shadow: 0 1px hsla(0, 0%, 0%, 0.5);
+}
diff --git a/core/themes/seven/seven.info.yml b/core/themes/seven/seven.info.yml
index 9452d5a9b9c3b85cf058e6bf61045aed3208ff82..993e0003d83d903928f2e150bda4af131565ebec 100644
--- a/core/themes/seven/seven.info.yml
+++ b/core/themes/seven/seven.info.yml
@@ -37,6 +37,8 @@ libraries-override:
   classy/dialog:
     seven/seven.drupal.dialog
 libraries-extend:
+  core/ckeditor:
+    - seven/ckeditor-dialog
   core/drupal.vertical-tabs:
     - seven/vertical-tabs
   core/jquery.ui:
diff --git a/core/themes/seven/seven.libraries.yml b/core/themes/seven/seven.libraries.yml
index a5b6d8afbf75518ab11fe9999bcbf1f43947d743..e68b75a916129ec574b19ec4202ee52ccf9464dd 100644
--- a/core/themes/seven/seven.libraries.yml
+++ b/core/themes/seven/seven.libraries.yml
@@ -93,6 +93,12 @@ seven.drupal.dialog:
     theme:
       css/components/dialog.css: {}
 
+ckeditor-dialog:
+  version: VERSION
+  css:
+    theme:
+      css/theme/ckeditor-dialog.css: {}
+
 tour-styling:
   version: VERSION
   css: