<!DOCTYPE html>
<html>
<head>
<title></title>
<style type="text/css">
html, body {
width:100%;
margin:0px auto;
padding:0px auto;
}
.div1 {
height:2000px;
}
.div2 {
width:100%;
height:35px;
background-color:#3399FF;
margin-top:500px;
}
.div2_1{
position:fixed;
width:100%;
height:35px;
z-index:999;
background-color:#3399FF;
top:0px;
_position:absolute;
_bottom:auto;
_top:expression(eval(document.documentElement.scrollTop));
}
*html{
background-image:url(about:blank);
background-attachment:fixed;
}
</style>
<script type="text/javascript">
window.onscroll=function(){
var t=document.documentElement.scrollTop||document.body.scrollTop;
var div2=document.getElementById("div2");
if(t>= 500){
div2.className = "div2_1";
}else{
div2.className = "div2";
}
}
</script>
</head>
<body>
<div class="div1">
<div id="div2" class="div2"></div>
</div>
</body>
</html>
