ISSUE 221 - Tabbing on search results in mobile

- In mobile view, when you tab through the search results and tab past
  the last result:
  - The focus goes to a 'close table of contents' button
- Update the SASS to hide the button when the search results are open.

lib/assets/stylesheets/modules/_search.scss

@@ -57,6 +57,10 @@ html.has-search-results-open {
   .app-pane__content {
     overflow: hidden;
   }
+
+  .toc__close{
+    display: none;
+  }
 }
 .search-results {
   display: none;