<!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>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<title>Document</title>
<style type="text/css">
.a{width: 200px;height: 200px;background: red;float: left;}
.a1{width: 150px;height: 150px;background: yellow;}
.b{width: 300px;height: 300px;background: blue;}
.b1{width: 250px;height: 220px;background: green;}
</style>
</head>
<body>
<div class="a">diva
<div class="a1">diva1</div>
</div>
<div class="b">
divb
<div class="b1">divb1</div>
</div>
div.a浮動之後，提高半個層級（比同級div.b高，但是和div.b內的所有文字是同級的）
</body>
</html>
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