网页效果：
HTML部分：
<body><ul class="nav"><li><a href="javascript:void(0);">菜单项目一</a><ul><li>子菜单项01</li><li>子菜单项02</li><li>子菜单项03</li><li>子菜单项04</li></ul></li><li><a href="javascript:void(0);">菜单项目二</a><ul><li>子菜单项01</li><li>子菜单项02</li><li>子菜单项03</li><li>子菜单项04</li></ul></li><li><a href="javascript:void(0);">菜单项目三</a><ul><li>子菜单项01</li><li>子菜单项02</li><li>子菜单项03</li><li>子菜单项04</li></ul></li><li><a href="javascript:void(0);">菜单项目四</a><ul><li>子菜单项01</li><li>子菜单项02</li><li>子菜单项03</li><li>子菜单项04</li></ul></li><li><a href="javascript:void(0);">菜单项目五</a><ul><li>子菜单项01</li><li>子菜单项02</li><li>子菜单项03</li><li>子菜单项04</li></ul></li></ul></body>
CSS部分：
ul,li {margin: 0px;padding: 0px;list-style: none;}a {text-decoration: none;}.nav {width: 450px;height: 40px;list-style: none;margin: 50px auto;line-height: 40px;background-color: #333;color: #fff;}.nav>li {width: 82px;margin: 0px 5px;float: left;text-align: center;}.nav>li>a {width: 82px;height: 40px;line-height: 40px;text-align: center;display: block;color: #FFFFFF;transition: all .5s;}.nav>li>a:hover {background-color: #0c8ed9;}.nav>li:first-child {margin-left: 0px;}.nav>li:last-child {margin-right: 0px;}.nav>li>ul {line-height: 30px;display: none;}.nav>li>ul>li {background: #333;color: #EEE;}.nav>li>ul>li:hover {background: #666;color: #FFF;cursor: pointer;}
JS部分：
$(document).ready(function() {var $nav = $(".nav>li");$nav.mouseover(function() {$(this).children("ul").show();});$nav.mouseout(function() {$(this).children("ul").hide();});});
