<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>回到顶部</title>
<style>
*{margin: 0;
padding: 0;
}
.container{
width: 1200px;
height: 100%;
/* margin:0 auto; */
}
.nav{
height: 80px;
}
.content{
height: 900px;
}
.footer{
height: 240px;
}
.header .container{
background-color: orange;
}
.nav .container{
background-color: gray;
}
.content .container{
background-color: yellow;
}
.footer .container{
background:
}
.on{
position: fixed;
top:0;
left: 0;
}
</style>
</head>
<body>
<div class="nav"><div class="container">导航</div></div>
<div class="content"><div class="container">内容</div></div>
<div class="footer"><div class="container">页脚</div></div>
<script src="http://libs.baidu.com/jquery/2.0.0/jquery.js" type="text/javascript" charset="utf-8"></script>
<script type="text/javascript">
$(function(){
var s=$(".content").offset().top;
$(window).scroll(function(){
var o=$(window).scrollTop();
if(o>s){
$(".nav").addClass("on");
}
})
})
</script>
</body>
</html>
