DIV垂直居中

<div class="col-xs-2" style="height: 214px;display: table;">
  <ul style="display: table-cell;vertical-align: middle;">
    <li style="text-align: center">
      <button type="button" id="buttonAdd" class="btn btn-info">添加</button>
    </li>
    <li>&nbsp;</li>
    <li style="text-align: center">
      <button type="button" id="buttonDel" class="btn btn-info">删除</button>
    </li>
  </ul>
</div>