<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
nav{
height: 30px;
width: 300px;
margin: 50px auto;
overflow: hidden;
transition: 2s;
border-radius: 15px;
}
nav:hover{
height: 180px;
}
h2{
background: orange;
color: white;
height: 30px;
line-height: 30px;
}
nav:hover h2{
background: black;
}
ul{
background: orange;
color: white;
}
ul li{
height: 30px;
line-height: 30px;
}
</style>
</head>
<body>
<nav>
<h2>菜单栏</h2>
<ul>
<li>首页</li>
<li>首页</li>
<li>首页</li>
<li>首页</li>
<li>首页</li>
</ul>
</nav>
</body>
</html>
原文：http://www.cnblogs.com/lhl66/p/7528355.html