一个css与js结合的下拉菜单支持主流浏览器

a:link{color:white;text-decoration:none;}
a:visited{color:white;text-decorative:none;}
a:hover{color:white;text-decorative:none;}
a:active{color:white;text-decorative:none;}
li{float:left;display:inline;background-color:#003366;width:120px;text-align:center;margin:2px;padding:10px 0 5px 0;position:relative;}
.limouseover{background-color:#0033ff;color:red;}
.limouseout{background-color:#003366;color:black;}
li ul{display:none;width:120px;position:absolute;left:0;top:30px;}
li ul li{margin:0px auto;border-top:1px solid #006699;}

<script language=javascript>
function menu(menu1){
//鼠标移入移出classname切换和子菜单隐藏、显示切换。
if (document.getElementById(menu1)){
var menu_ul=document.getElementById(menu1);
if (menu_ul.getElementsByTagName("li").length){
var menu_li=menu_ul.getElementsByTagName("li");
for (i in menu_li){
menu_li[i].onmouseover=function(){this.className="limouseover";if (this.getElementsByTagName("ul").length){this.getElementsByTagName("ul")[0].style.display="block";}}
menu_li[i].onmouseout=function(){this.className="limouseout";if (this.getElementsByTagName("ul").length){this.getElementsByTagName("ul")[0].style.display="none";}}
}
}
}
}

</script>

<ul id=menu1>
<li><a href="">首页</a></li>
<li><a href="">菜单1菜单1</a>
<ul>
<li><a href="">子菜单1子菜单1子菜单1子菜单1</a></li>
<li><a href="">子菜单2</a></li>
</ul>
</li>
<li><a href="">菜单2</a>
<ul>
<li><a href="">子菜单1子菜单1子菜单1子菜单1</a></li>
<li><a href="">子菜单2</a></li>
</ul>
</li>
</ul>