code: function updateScrollButtonVisibility(hideAll) {
  		if (hideAll && this._topScrollButton && this._bottomScrollButton) {
  			this._topScrollButton.style.display = "none";
  			this._bottomScrollButton.style.display = "none";	
  		}
  		else if (!hideAll) {
  			if (this._dropdownNode.scrollTop > 0) {
  				this._topScrollButton.style.display = "block";
  			} 
  			else {
  				this._topScrollButton.style.display = "none";
  			}	
  			if (this._dropdownNode.scrollHeight > this._dropdownNode.scrollTop + this._dropdownNode.offsetHeight) {
  				this._bottomScrollButton.style.display = "block";
  			}	 
  			else {
  				this._bottomScrollButton.style.display = "none";
  			}
  		}
  	}
docs: Hides or shows the scroll buttons
  @param {Boolean} hideAll True if hiding both buttons. Required.