Include documentsearch CSS in the notebook example

examples/notebook/src/index.ts

@@ -8,6 +8,7 @@ __webpack_public_path__ = URLExt.join(PageConfig.getBaseUrl(), 'example/');
 import '@jupyterlab/application/style/index.css';
 import '@jupyterlab/codemirror/style/index.css';
 import '@jupyterlab/completer/style/index.css';
+import '@jupyterlab/documentsearch/style/index.css';
 import '@jupyterlab/notebook/style/index.css';
 import '@jupyterlab/theme-light-extension/style/index.css';
 import '../index.css';