css 이미지 수평중앙정렬

<div style="width:55%;height:400px;margin-top:30px;float:left; display: table; vertical-align:middle; ">     <div style=" display:table-cell; vertical-align:middle; "> <img src="admin/pdt_img/big01.png" id="top_center_img" />  </div> </div>