css3实现带有简单动画按钮导航

<div class="content">
 <h2>Simple Animated Menu Using CSS3</h2>
 <h3>Example 1</h3>
 <ul class="nav">
 <li class="selected"><a href="http://www.php1.cn/"> <li><a href="http://www.php1.cn/"> <li><a href="http://www.php1.cn/"> <li><a href="http://www.php1.cn/"> </ul>
 <br /><br />
 <br /><br />
 <div style="clear:both;"></div>
 <h3>Example 2</h3>
<ul class="nav2">
 <li><a href="http://www.php1.cn/"> <li><a href="http://www.php1.cn/"> <li><a href="http://www.php1.cn/"> <li><a href="http://www.php1.cn/"> </ul>
</div>

<style type="text/css">
* {
 margin:0;
 padding:0;
}
body {
 background:#eee;
 font-family:Verdana, Geneva, sans-serif;
 font-size:12px;
}
a {
 text-decoration:none;
}
h2, h3 {
 margin:0 0 20px;
 text-shadow:2px 2px #ffffff;
}
h2 {
 font-size:28px;
}
h3 {
 font-size:22px;
}
.content {
 padding:40px;
 width:500px;
 margin:30px auto;
}
.nav {
 list-style:none;
}
.nav li {
 float:left;
}
.nav a {
 position:relative;
 display:block;
 padding:4px 8px;
 border-bottom:2px solid #ccc;
 background:#f4f4f4;
 color:#999;
 -webkit-transition:all 200ms ease-out;
 -moz-transition:all 200ms ease-out;
 -o-transition:all 200ms ease-out;
 transition:all 200ms ease-out;
}
.nav a:hover {
 color:#000;
 background:#fff;
 border-color:#000;
 padding:8px;
 top:-4px;
}
.nav .selected a, .nav .selected a:hover {
 background:#444;
 color:#fff;
 border-color:#000;
}
.nav2 {
 list-style:none;
}
.nav2 li {
 float:left;
 position:relative;
}
.nav2 a {
 display:block;
 float:left;
 border:none;
 position:relative;
 height:22px;
 overflow:hidden;
}
.nav2 a strong, .nav2 a em {
 cursor:pointer;
 padding:4px 8px;
 font-weight:bold;
 font-style:normal;
 display:block;
 -webkit-transition:all 200ms ease-out;
 -moz-transition:all 200ms ease-out;
 -o-transition:all 200ms ease-out;
 transition:all 200ms ease-out;
}
.nav2 a strong {
 position:relative;
 top:0;
 left:0;
 color:#000;
 background:#fff;
}
.nav2 em {
 position:absolute;
 top:100%;
 background:#000;
 color:#fff;
}
.nav2 a:hover strong {
 top: -100%;
}
.nav2 a:hover em {
 top: 0;
}
</style>