html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>导航栏</title>
<link rel="stylesheet" href="css/test.css" />
<script type="text/javascript" src="js/jquery-1.11.3.min.js" ></script>
</head>
<body>
<div class="nav">
<ul class="list">
<li><a href="#">首页</a></li>
<li><a href="#">职业课程</a>
<div class="down">
<a href="#">课程库</a>
<a href="#">知识体系图</a>
<a href="#">职业路径图</a>
<a href="#">系列课程</a>
</div>
</li>
<li>
<a href="#">就业学习</a>
<div class="down">
<a href="#">Web前端开发</a>
<a href="#">Android开发</a>
<a href="#">JavaWeb开发</a>
</div>
</li>
<li>
<a href="#">极客社区</a>
<div class="down">
<a href="#">wiki</a>
<a href="#">技术问答</a>
<a href="#">社群</a>
<a href="#">资源分享</a>
</div>
</li>
<li>
<a href="#">极客+</a>
<div class="down">
<a href="#">高校合作</a>
<a href="#">极客人才联盟</a>
</div>
</li>
</ul>
</div>
</body>
</html>
css
*{padding:0; margin:0;}
li{ list-style:none}
a{ text-decoration:none;}
.nav{ 100%; height:40px; background:#222; margin-top:100px;}
.nav .list{ 1000px; height:40px;margin:0 auto;}
.list li{ float:left; position:relative;}
.list li>a{ padding:0 30px; line-height:40px; display:block; color:#aaa; font-size:16px;}
.list li:hover>a{ background:#333; color:#fff;}
.list li:hover .down{ display:block;}
.list li .down{ 150px; background:#333; position:absolute; top:40px;left:0; display:none;}
.list li .down a{ display:block; line-height:30px; color:#aaa; font-size:14px; padding-left:30px;}
.list li .down a:hover{ color:#fff;}
效果：
