add separator before milestone reference in collapsed view

app/assets/stylesheets/pages/milestone.scss

@@ -66,6 +66,12 @@
   .milestone-stat:last-child {
     margin-right: 0;
   }
+
+  .right-sidebar-collapsed & {
+    .reference {
+      border-top: 1px solid $border-gray-normal;
+    }
+  }
 }
 
 .milestone-summary {

app/views/shared/milestones/_sidebar.html.haml

@@ -96,7 +96,7 @@
 
     - milestone_ref = milestone.try(:to_reference, full: true)
     - if milestone_ref.present?
-      .block
+      .block.reference
         .sidebar-collapsed-icon.dont-change-state
           = clipboard_button(clipboard_text: milestone_ref, title: "Copy reference to clipboard", placement: "left")
         .cross-project-reference.hide-collapsed