Make the privacy dropdown button not look strange when using top placement

Inspired by 8fe1f8d4ce

app/javascript/flavours/glitch/features/composer/options/dropdown/index.js

@@ -168,6 +168,7 @@ export default class ComposerOptionsDropdown extends React.PureComponent {
     const computedClass = classNames('composer--options--dropdown', {
       active,
       open,
+      top: placement === 'top',
     });
 
     //  The result.

app/javascript/flavours/glitch/styles/components/composer.scss

@@ -406,6 +406,12 @@
       background: $ui-highlight-color;
       transition: none;
     }
+    &.top {
+      & > .value {
+        border-radius: 0 0 4px 4px;
+        box-shadow: 0 4px 4px rgba($base-shadow-color, 0.1);
+      }
+    }
   }
 }