css问题

<style type="text/css">
<!--
#zt1 div {
    border: 1px solid #FF0000;
}

#zt1 {
    position:relative;
    top:9px;
    width:950px;
    height:auto;
    z-index:1;
    margin:auto;
}
#zt1left {
    position:relative;
    float:left;
    width:215px;
    height:auto;
    z-index:1;
    overflow:hidden;
}
#zt1mid {
    position:relative;
    float:left;
    margin-left:5px;
    width:510px;
    height:auto;
    z-index:1;
    overflow: hidden;
}
#zt1right {
    position:relative;
    float:left;
    margin-left:5px;
    width:215px;
    height:auto;
    z-index:1;
    overflow:hidden;
}
-->
</style>

<div id="zt1">

<div id="zt1left">
八大菜系<br />
123<br />
123<br />
123<br />
123<br />
123<br />
123<br />
123<br />
123<br />
123<br />
123<br />
123<br />
123<br />
</div>

<div id="zt1mid">
列表<br />
456<br />
456<br />
</div>

<div id="zt1right">
<br />
<br />
<br />
<br />
<br />
<br />
<br />
</div>

</div>