利用JS来改变div的高度

var contextBlockHeight = document.getElementById(\'contextBlock\').clientHeight;
if ( contextBlockHeight > 430) {
    contextBlockHeight = contextBlockHeight + 50;
    document.getElementById(\'middleContextBlock\').style.height = contextBlockHeight + "px";
}

<div id="contextBlock" class="mTop5 contextArea fontSize13">

</div>