diff --git a/core/modules/system/system.base.css b/core/modules/system/system.base.css
index 5bbde172733a7a06ce5f56dce52ca0a01383bc5e..a0b66e65f0962e445b49f23ccd29b2e519bcf328 100644
--- a/core/modules/system/system.base.css
+++ b/core/modules/system/system.base.css
@@ -288,6 +288,7 @@ figure,
 footer,
 header,
 hgroup,
+main,
 menu,
 nav,
 section,