PLT-6614 - Mentions badge styling and dropdown icon style (#6426)

* Mentions badge styling and dropdown icon style

* PLT-6134 - Fixing emoji picker border in RHS

webapp/sass/layout/_sidebar-left.scss

@@ -53,7 +53,7 @@
         padding: 1em 1em 0;
     }
 
-    .badge {
+    .mention-badge {
         background-color: $primary-color;
         position: absolute;
         right: 10px;

webapp/sass/layout/_team-sidebar.scss

@@ -54,7 +54,7 @@
                         width: 31px;
                     }
 
-                    .badge {
+                    .mention-badge {
                         font-size: 10px;
                         position: absolute;
                         right: -6px;