Scroll doc sidebar not whole page

Reviewed By: danielbuechele

Differential Revision: D6976133

fbshipit-source-id: 7807aa4e2ab0ed013fbd1f4bbef2ee1b8098dff6

website/src/templates/withPlayground.js

@@ -20,7 +20,7 @@ import {Button, Icon, Row, Col} from 'antd';
 import './index.css';
 
 export default ({pathContext}) => (
-  <Page className="doc-block">
+  <Page className="doc-block playground">
     <Playground
       selectedNodePath={[]}
       showGuides={false}