Highlight "Jump to Bottom" badge when appropriate

This resolves https://github.com/vector-im/riot-web/issues/13135

Signed-off-by: Mike Pennisi <mike@mikepennisi.com>

src/components/views/rooms/JumpToBottomButton.js

@@ -16,13 +16,18 @@ limitations under the License.
 
 import { _t } from '../../../languageHandler';
 import AccessibleButton from '../elements/AccessibleButton';
+import classNames from 'classnames';
 
 export default (props) => {
+    const className = classNames({
+        'mx_JumpToBottomButton': true,
+        'mx_JumpToBottomButton_highlight': props.highlight,
+    });
     let badge;
     if (props.numUnreadMessages) {
         badge = (<div className="mx_JumpToBottomButton_badge">{props.numUnreadMessages}</div>);
     }
-    return (<div className="mx_JumpToBottomButton">
+    return (<div className={className}>
         <AccessibleButton className="mx_JumpToBottomButton_scrollDown"
             title={_t("Scroll to most recent messages")}
             onClick={props.onScrollToBottomClick}>