一个简单的盒子模型展示
<html>
<head>
<meat charset=utf-8 />
<title>盒模型</title>
</head>
<body>
<div class="box-top" style="width=100px height=200px background-color=blue"></div>
<div class="box-bottom" style="width=200px height=400px background-color=green"></div>
</body>
</html>