<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>css</title>
<style type="text/css">
.laoLiu{
width:200px;height:200px;background:#E1EFFF;
margin-left:20px;
margin-right:20px;
margin-bottom:20px;
margin-top:20px;
}
</style>
</head>
<body>
<div style="background:gray;height:20px;"></div>
<div class="laoLiu"></div>
<div style="background:purple;height:20px;"></div>
</body>
</html>
返回值：