<!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"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>动画菜单</title><style type="text/css">* { margin: 0; padding: 0; font-size: 14px; }a { color: #333; text-decoration: none }ul{ list-style: none; }.nav {height: 30px; border-bottom: 5px solid #F60; margin-left:50px; width:600px;}.nav li { float: left; position:relative; height:30px; width:120px }.nav li a { display: block; height: 30px; text-align: center; line-height: 30px; width:120px; background: #efefef; margin-left: 1px; }.subNav{ position:absolute; top:30px; left:0; width:120px; height:0; overflow:hidden}.subNav li a{ background:#ddd }.subNav li a:hover{ background:#efefef}</style><script>window.onload=function(){var aLi=document.getElementsByTagName(‘li‘);for(var i=0; i<aLi.length; i++){aLi[i].onmouseover=function(){var oSubNav=this.getElementsByTagName(‘ul‘)[0];if(oSubNav){var This=oSubNav;clearInterval(This.time);This.time=setInterval(function(){This.style.height=This.offsetHeight+16+"px";if(This.offsetHeight>=120)clearInterval(This.time);},30)}}}//鼠标离开菜单，二级菜单动画收缩起来。aLi[i].onmouseout=function(){}}}</script></head><body><ul class="nav"><li><a href="#">一级菜单</a><ul class="subNav"><li><a href="#">二级菜单</a></li><li><a href="#">二级菜单</a></li><li><a href="#">二级菜单</a></li><li><a href="#">二级菜单</a></li></ul></li><li><a href="#">一级菜单</a><ul class="subNav"><li><a href="#">二级菜单</a></li><li><a href="#">二级菜单</a></li><li><a href="#">二级菜单</a></li><li><a href="#">二级菜单</a></li></ul></li><li><a href="#">一级菜单</a></li><li><a href="#">一级菜单</a></li><li><a href="#">一级菜单</a></li></ul></body></html>
原文：http://www.cnblogs.com/TT-Cartier/p/4697205.html