Fixing attachment in RHS root post for compact view (#3289)

* Fixing attachment in RHS root post for compact view

* Improving spacing for mentions

webapp/sass/components/_mentions.scss

@@ -13,10 +13,10 @@
     @include clearfix;
     cursor: pointer;
     font-size: 13px;
-    height: 36px;
-    line-height: 36px;
-    margin: 5px 0;
-    padding: 2px;
+    height: 39px;
+    line-height: 35px;
+    margin: 0;
+    padding: 3px 8px;
     position: relative;
     white-space: nowrap;
     width: 100%;