css3 implements button navigation with simple animation

<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>