message: Focus field after using `collapsible-content-button`
diff: @@ -42,6 +42,7 @@ function addContentToDetails(event: delegate.Event<MouseEvent, HTMLButtonElement
  </details>
  `.replace(/(\n|\b)\t+/g, '$1').trim();
  + field.focus();
  textFieldEdit.insert(field, smartBlockWrap(newContent, field));
  // Restore selection.
  