一个用纯CSS实现的下拉菜单

用CSS做下拉列表的特效，代码如下：
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">

    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
        <title></title>
        <style type="text/css">
            * {
                margin: 0px;
                padding: 0px;
            }
            
            #nav {
                width: 500px;
                background-color: #737373;
                height: 40px;
                /*border-radius: 10px;*/
                position: relative;
                margin: 0px auto;
                top: 0px;
            }
            
            .nav-container {
                width: 100%;
                height: 40px;
                position: absolute;
            }
            
            .banner {
                float: left;
                text-align: center;
                height: 40px;
                width: 20%;
                line-height: 40px;
            }
            
            .banner:hover {
                background-color: #00BFFF;
                cursor: pointer;
            }
            
            div ul {
                list-style: none;
                /*display: none;*/
                background-color: blue;
                overflow: hidden;
                /*模拟height:auto时候的情况*/                
                max-height: 0px;
                transition: max-height 0.3s;
                /*多浏览器支持*/
                -moz-transition: height 1s;
                -webkit-transition: height 1s;
                -o-transition: height 1s;
            }
            
            .banner:hover ul {
                /*display: block;*/
                width: 100%;
                max-height: 160px;
            }
            
            div ul li {
                overflow: hidden;
            }
            
            div ul li:hover {
                background-color: red;
            }
        </style>
    </head>

    <body>
        <div class="nav-container">
            <div id="nav">
                <div id="nav-button-1" class="banner">第1个导航
                    <ul>
                        <li>1</li>
                        <li>2</li>
                        <li>3</li>
                        <li>4</li>
                    </ul>
                </div>
                <div id="nav-button-2" class="banner">第2个导航
                    <ul>
                        <li>1</li>
                        <li>2</li>
                        <li>3</li>
                    </ul>
                </div>
                <div id="nav-button-3" class="banner">第3个导航
                    <ul>
                        <li>1</li>
                        <li>2</li>
                    </ul>
                </div>
                <div id="nav-button-4" class="banner">第4个导航
                    <ul>
                        <li>1</li>
                        <li>2</li>
                        <li>3</li>
                        <li>4</li>
                        <li>5</li>
                    </ul>
                </div>
                <div id="nav-button-5" class="banner">第5个导航
                    <ul>
                        <li>1</li>
                        <li>2</li>
                        <li>3</li>
                        <li>4</li>
                        <li>5</li>
                    </ul>
                </div>
            </div>
        </div>

    </body>

</html>
效果如下：
这就是做出来的样子，当然可以做成横向列表，自己试着做一下。