[PLT-4374] Added active state for recent mentions and flagged posts. (#6253)

* [PLT-4374] Added active state for recent mentions and flagged posts.

* Increased hover opacity to 0.7 on mention and flag icon.

webapp/sass/layout/_headers.scss

@@ -462,12 +462,20 @@
             text-decoration: none;
 
             &:hover {
-                @include opacity(1);
+                @include opacity(0.7);
             }
 
             &:focus {
                 color: inherit;
             }
+
+            &.active {
+                color: $primary-color;
+                @include opacity(1);
+                .icon {
+                    fill: $primary-color;
+                }
+            }
         }
     }