getOverlayContainerStopEvent() {
    return this.overlayContainerStopEvent_;
  }
Get the element that serves as a container for overlays that don't allow
event propagation. Elements added to this container won't let mousedown and
touchstart events through to the map, so clicks and gestures on an overlay
don't trigger any {@link module:ol/MapBrowserEvent~MapBrowserEvent}.
@return {!HTMLElement} The map's overlay container that stops events.