Issue #3096203 by bnjmnm, xjm, lauriii: Create Classy library dependency tests...

Issue #3096203 by bnjmnm, xjm, lauriii: Create Classy library dependency tests that can be used for all themes, and verify by providing an Umami-specific classy/dropbutton

core/profiles/demo_umami/themes/umami/css/classy/components/dropbutton.css

+/**
+ * @file
+ * General styles for dropbuttons.
+ */
+
+.js .dropbutton-widget {
+  border: 1px solid #ccc;
+  background-color: white;
+}
+.js .dropbutton-widget:hover {
+  border-color: #b8b8b8;
+}
+.dropbutton .dropbutton-action > * {
+  padding: 0.1em 0.5em;
+  white-space: nowrap;
+}
+.dropbutton .secondary-action {
+  border-top: 1px solid #e8e8e8;
+}
+.dropbutton-multiple .dropbutton {
+  border-right: 1px solid #e8e8e8; /* LTR */
+}
+[dir="rtl"] .dropbutton-multiple .dropbutton {
+  border-right: 0 none;
+  border-left: 1px solid #e8e8e8;
+}
+.dropbutton-multiple .dropbutton .dropbutton-action > * {
+  margin-right: 0.25em; /* LTR */
+}
+[dir="rtl"] .dropbutton-multiple .dropbutton .dropbutton-action > * {
+  margin-right: 0;
+  margin-left: 0.25em;
+}

core/profiles/demo_umami/themes/umami/umami.info.yml

@@ -11,6 +11,7 @@ libraries:
 
 libraries-override:
   classy/messages: false
+  classy/dropbutton: umami/classy.dropbutton
   layout_builder/twocol_section:
     css:
       theme:
@@ -27,6 +28,8 @@ libraries-override:
 libraries-extend:
   tour/tour-styling:
     - umami/demo-umami-tour
+  core/drupal.dropbutton:
+    - umami/classy.dropbutton
 
 regions:
   pre_header: Pre-header

core/profiles/demo_umami/themes/umami/umami.libraries.yml

@@ -130,3 +130,9 @@ oneplusfourgrid_section:
   css:
     theme:
       layouts/oneplusfourgrid_section/oneplusfourgrid_section.css: {}
+
+classy.dropbutton:
+  version: VERSION
+  css:
+    component:
+      css/classy/components/dropbutton.css: { weight: -10 }