<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<style>
#back{
width: 100px;
height: 100px;
background-color: thistle;
text-align: center;
line-height: 100px;
position: fixed;
bottom: 20px;
right: 20px;
z-index: 1000;
}
</style>
<title>固定定位</title>
</head>
<body>
<div style="height: 1000px">
<div id="back">
返回顶部
</div>
</div>
</body>
</html>
