css实现的让图片垂直居中的方法

<div id="box">
    <span><img src="images/demo.jpg" alt=""></span>
</div>

<style type="text/css">
#box{
width:500px;height:400px;
display:table;
text-align:center;
border:1px solid #d3d3d3;background:#fff;
}
#box span{
display:table-cell;
vertical-align:middle;
}
#box img{
border:1px solid #ccc;
}
</style>
<!--[if lte IE 7]>
<style type="text/css">
#box{
position:relative;
overflow:hidden;
}
#box span{
position:absolute;
left:50%;top:50%;
}
#box img{
position:relative;
left:-50%;top:-50%;
}
</style>
<![endif]-->

<style type="text/css">
#box{
width:500px;height:400px;
overflow:hidden;
position:relative;
display:table-cell;
text-align:center;
vertical-align:middle;
border:1px solid #d3d3d3;background:#fff;
}
#box span{
position:static;
*position:absolute; /*针对IE6/7的Hack*/
top:50%; /*针对IE6/7的Hack*/
}
#box img {
position:static;
*position:relative; /*针对IE6/7的Hack*/
top:-50%;left:-50%; /*针对IE6/7的Hack*/
border:1px solid #ccc;
}
</style>