UX: Fix mobile styling for admin color schemes (#14314)

app/assets/javascripts/admin/addon/templates/customize-colors-show.hbs

@@ -17,7 +17,7 @@
         label="admin.customize.copy"
       }}
       {{d-button
-        class="btn-default"
+        class="btn-default copy-to-clipboard"
         action=(action "copyToClipboard" model)
         icon="far-clipboard"
         label="admin.customize.copy_to_clipboard"
@@ -38,8 +38,6 @@
       {{/if}}
     </div>
 
-    <br>
-
     <div class="admin-controls">
       {{#unless model.theme_id}}
         <div class="pull-right">