CSS-三栏自适应高度

<div>
    <div class="leftSide">左边栏</div>
    <div class="rightSide">右边栏</div>
    <div class="middAuto">中间自适应部分</div>
</div>

.leftSide{
    float: left;
    display: inline;
    width: 250px;
    background-color: #fff;
    border: 1px solid #c8c8c8;
    padding-bottom: 20000px;
    margin-bottom: -20000px;
}

.rightSide{
    float: right;
    display: inline;
    width: 260px;
    background-color: #fff;
    padding-bottom: 20000px;
    margin-bottom: -20000px;
}

.middAuto{    
    background-color: #c5c5c5;
    padding-bottom: 20000px;
    margin-bottom: -20000px;
}