[html]三列居中自动伸缩的结构

<div style="width:100%;height:80px;border:1px solid #DDD;margin-bottom:10px;">Header</div>
<div> 
    <div style="width:200px;height:300px;border:1px solid #DDD;float:left;">Left</div>
    <div style="width:200px;height:300px;border:1px solid #DDD;float:right;">Right</div>
    <div style="width:auto;height:300px;border:1px solid #DDD;margin-left:210px;margin-right:210px;margin-top:0px;">Middle</div>
</div>