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>