Minor UI improvements (#4431)

webapp/sass/components/_dropdown.scss

@@ -15,6 +15,10 @@
 
     .divider {
         @include opacity(.15);
+
+        &:last-child {
+            display: none;
+        }
     }
 
     div,

webapp/sass/components/_modal.scss

@@ -73,6 +73,10 @@
             }
         }
 
+        .alert {
+            margin-bottom: 0;
+        }
+
         .custom-textarea {
             border-color: $light-gray;
             color: inherit;