在ionic中 textarea怎么垂直居中

  <div style="color: #9F9F9F;vertical-align:middle; _position:absolute;
        _top:50%;  ">

                    <textarea placeholder="If your shipment is not heavy but large in size, Please specify here within 20 character" 
                              style="padding-left:10px; width:100%;font-size:12px;height:30px; line-height:15px;vertical-align:middle; display:table-cell;" ng-model="order.Comments"></textarea>
                </div>

            <div style="color: #9F9F9F;vertical-align:middle; _position:absolute;
    _top:50%;  ">

                <textarea placeholder="If your shipment is not heavy but large in size, Please specify here within 20 character" style="padding-left:10px; width:100%;font-size:12px;height:30px; line-height:15px;vertical-align:middle; display:table-cell;" ng-model="order.Comments"></textarea>
            </div>
        </div>
    </div>

textarea也absolute定位，top 50%,margin-top:(-高度/2)px

 <div style="color: #9F9F9F;vertical-align:middle; _position:absolute;
        _top:50%;  ">

    <textarea placeholder="If your shipment is not heavy but large in size, Please specify here within 20 character"
              style="position:absolute;top:50%;margin-top:-15px;padding-left:10px; width:100%;font-size:12px;height:30px; line-height:15px;vertical-align:middle; display:table-cell;" ng-model="order.Comments"></textarea>
</div>