code: function moveDropdown () {
      if (!elements.$.root.length) return;
      $mdTheming(elements.$.scrollContainer);
      elements.$.scrollContainer.detach();
      elements.$.root.append(elements.$.scrollContainer);
      if ($animate.pin) $animate.pin(elements.$.scrollContainer, $rootElement);
    }
docs: Moves the dropdown menu to the body tag in order to avoid z-index and overflow issues.