<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style>
body{
padding:0px;
margin:0px;
}
#wrap{
height:2000px;
}
.ad{
height:200px;
width:50px;
background:pink;
position:fixed;
}
.left{
left:0px;
}
.right{
right:0px;
}
</style>
<script type="text/javascript">
window.onload = function ()
{
var oad = document.getElementsByClassName('ad');
oad[0].style.top = oad[1].style.top = (document.documentElement.clientHeight - oad[0].offsetHeight)/2 + 'px';
};
</script>
</head>
<body>
<div id="wrap">
<div class="ad left"></div>
<div class="ad right"></div>
</div>
</body>
</html>
