Need access to popupContainer element.

I am using rc-slider and I need to set the z-index for the element created by getContainer.
I also propose putting this logic inside componentDidMount() and clean up in componentWillUnmount.

Alternatively you could set the styling for the element within the portal. Right now it's a bit tricky to work with.

getContainer = () => {
  const { props } = this;
  const popupContainer = document.createElement('div');
  // Make sure default popup container will never cause scrollbar appearing
  // https://github.com/react-component/trigger/issues/41
  popupContainer.style.position = 'absolute';
  popupContainer.style.top = '0';
  popupContainer.style.left = '0';
  popupContainer.style.width = '100%';
  const mountNode = props.getPopupContainer ?
    props.getPopupContainer(findDOMNode(this)) : props.getDocument().body;
  mountNode.appendChild(popupContainer);
  return popupContainer;
}

まず、trigger コード内の getContainer 実装を見つけ、ポップアップコンテナがどのように作成および削除されるかを確認します。呼び出し元が作成されたコンテナにアクセスしたりスタイルを適用したりでき、そのライフサイクルの動作が関連する既存のテストでカバーされれば、issue は完了です。