Css控制div水平垂直居中显示

<style>
#info{height:0px; width:0px;top:50%; left:50%;position:absolute;}
#center{background:#FFCC33;border:1px solid #0033FF; width:300px;height:300px;position:absolute; margin:-150px;}
</style>
<div id="info">
<div id="center">www.aa25.cn</div>
</div>