回到頂部-

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
??? <title>Javascript 回到頂部效果</title>
?<style >
.box {
??? width:1190px;
??? margin:0 auto;
??? }
#btn {
??? width:40px;
??? height:40px;
??? position:fixed;
??? left:50%;
??? margin-left:590px;
??? bottom:30px;
??? background:url(http://img1.sycdn.imooc.com//535e0dc100010e9c00400080.jpg) no-repeat left top;
??? margin:0 auto;
??? }
#btn:hover {
??? background:url(http://img1.sycdn.imooc.com//535e0dc100010e9c00400080.jpg) no-repeat 0 -40px;
??? }
</style>
</head>
<body>
?
?<div>
??<img src="http://img1.sycdn.imooc.com//535e0ce800015b7511902787.jpg" />
?</div>
?<a href="javascript:;" id="btn" title="回到頂部"></a>
</body>
</html>