diff -u b/core/themes/seven/seven.libraries.yml b/core/themes/seven/seven.libraries.yml
--- b/core/themes/seven/seven.libraries.yml
+++ b/core/themes/seven/seven.libraries.yml
@@ -75,14 +75,14 @@
 vertical-tabs:
   version: VERSION
   css:
-    theme:
+    component:
       css/components/vertical-tabs.css: {}
 
 seven.jquery.ui:
   version: VERSION
   css:
-    theme:
-      css/components/jquery.ui/theme.css: {}
+    component:
+      css/components/jquery.ui/theme.css: { weight: -1 }
 
 seven.drupal.dialog:
   version: VERSION
diff -u b/core/themes/seven/seven.theme b/core/themes/seven/seven.theme
--- b/core/themes/seven/seven.theme
+++ b/core/themes/seven/seven.theme
@@ -207,11 +207,11 @@
     $libraries['drupal.vertical-tabs']['dependencies'][] = 'seven/vertical-tabs';
   }
   if (isset($libraries['jquery.ui'])) {
-    unset($libraries['jquery.ui']['css']['component']['assets/vendor/jquery.ui/themes/base/theme.css']);
+    unset($libraries['jquery.ui']['css']['theme']['assets/vendor/jquery.ui/themes/base/theme.css']);
     $libraries['jquery.ui']['dependencies'][] = 'seven/seven.jquery.ui';
   }
   if (isset($libraries['drupal.dialog'])) {
-    unset($libraries['drupal.dialog']['css']['component']['misc/dialog.theme.css']);
+    unset($libraries['drupal.dialog']['css']['theme']['misc/dialog.theme.css']);
     $libraries['drupal.dialog']['dependencies'][] = 'seven/seven.drupal.dialog';
   }
 }