diff -u b/core/themes/seven/seven.info.yml b/core/themes/seven/seven.info.yml
--- b/core/themes/seven/seven.info.yml
+++ b/core/themes/seven/seven.info.yml
@@ -10,6 +10,7 @@
  - seven/global-styling
 stylesheets-remove:
   - core/assets/vendor/jquery.ui/themes/base/dialog.css
+  - @classy/css/layout.css
 quickedit_stylesheets:
   - css/components/quickedit.css
 regions:
only in patch2:
unchanged:
--- a/core/themes/bartik/bartik.info.yml
+++ b/core/themes/bartik/bartik.info.yml
@@ -5,6 +5,8 @@ description: 'A flexible, recolorable theme with many regions and a responsive,
 package: Core
 version: VERSION
 core: 8.x
+stylesheets-remove:
+  - @classy/css/layout.css
 libraries:
   - bartik/global-styling
 ckeditor_stylesheets: