clean install

web/core/themes/claro/js/dropbutton.js

@@ -0,0 +1,23 @@
+/**
+ * @file
+ * Theme overrides for Claro.
+ */
+
+((Drupal) => {
+  /**
+   * Overrides the dropbutton toggle markup.
+   *
+   * We have to keep the 'dropbutton-toggle' CSS class because the dropbutton JS
+   * operates with that one.
+   *
+   * @param {object} options
+   *   Options object.
+   * @param {string} [options.title]
+   *   The button text.
+   *
+   * @return {string}
+   *   A string representing a DOM fragment.
+   */
+  Drupal.theme.dropbuttonToggle = (options) =>
+    `<li class="dropbutton-toggle"><button type="button" class="dropbutton__toggle"><span class="visually-hidden">${options.title}</span></button></li>`;
+})(Drupal);