Remove absolute document search pane width

Closes #9178

packages/documentsearch/style/base.css

@@ -17,7 +17,6 @@
   top: 0;
   right: 0;
   z-index: 7;
-  width: 405px;
   padding: 2px;
   font-size: var(--jp-ui-font-size1);
 }