css mainDiv和popbox居中

<style>

     .beCenter {

         width:460px;

         height:212px;

         background:#ccc;

         margin:0px auto;

     }

     .beAllCenter{

         width:460px;

         height:212px;

         background:#f00;

         margin-left:-230px;

         margin-top:-106px;

         position:absolute;

         top:50%;

         left:50%;

     }

</ style >

< div  style="width:800px; height:600px; text-align:center; position:relative">

     < div  class="beCenter"></ div >

     < div  class="beAllCenter"></ div >

</ div >