css实现垂直水平居中

HTML:

<div class="wrapper">  <div class="content"></div></div>

CSS:

.wrapper {   position:relative;   width:500px;   height:500px;   background:#ddd; }.content {   width:200px;   height:200px;   position:absolute;   top:50%;   left:50%;   margin-top:-100px;   margin-left:-100px;}