CSS下拉框的做法，定位的应用。
HTML内容：
<!DOCTYPE html>
<html>
<head>
<title>淘宝导航</title>
<meta charset="utf-8">
<link rel="shortcut icon" type="image/x-icon" href="">
<link rel="stylesheet" type="text/css" href="index.css">
</head>
<body>
<div class="header">
<div class="header_content">
<div class="header_left">
<a href="" class="header_a">中国大陆 <i class="fa fa-angle-down"></i></a>
<a href="" style="color: #FF5000;">亲，请登录</a>
<a href="">免费注册</a>
<a href="">手机逛淘宝</a>
</div>
<div class="header_right">
<a href="" class="header_a">我的淘宝 <i class="fa-angle-down"></i>
<ul>
<li>已买到的宝贝</li>
<li>我的足迹</li>
</ul>
</a>
<a href="" class="header_a"><span class="fa fa-cart-plus" style="color: #FF5000"></span> 购物车</a>
<a href="" class="header_a"> 收藏夹 <i class="fa-angle-down"></i>
<ul>
<li>收藏的宝贝</li>
<li>收藏的店铺</li>
</ul>
</a>
<a href="">商品分类</a>
<a href="" class="header_a">卖家中心 <i class="fa-angle-down"></i>
<ul>
<li>免费开店</li>
<li>已卖出的宝贝</li>
<li>出售中的宝贝</li>
<li>卖家服务市场</li>
<li>卖家培训中心</li>
<li>体检中心</li>
<li>问商友</li>
</ul>
</a>
<a href="" class="header_a">联系客服 <i class="fa-angle-down"></i>
<ul>
<li>消费者客服</li>
<li>卖家客服</li>
</ul>
</a>
<a href="" class="header_a"><span class="fa fa-align-justify"></span>网站导航 <i class="fa-angle-down"></i></a>
</div>
<div class="clear"></div>
</div>
<div class="clear"></div>
</div>
</body>
</html>
CSS内容：
*{margin: 0px;padding: 0px;}
a{text-decoration: none;color: #6c6c6c;font-size: 13px;}
li{list-style: none;}/*去掉样式*/
.clear{clear: both;}
.header{width: 100%;background-color: #F5F5F5;}
.header_content{width: 1200px;margin: 0px auto;line-height: 0px;line-height: 40px;}
.header_left{height: 40px;float: left;}
.header_left a{margin-right: 5px;}
.header_content a:hover{color: #FF5000;}
.header_right{height: 40px;float: right;}
.header_a{display: inline-block;width: 90px;height: 40px;text-align: center;position: relative;}
.header_a:hover{background-color: #fff}
.header_a ul{border: 1px solid #F5F5F5;display: none; border-top: none;}
.header_a:hover ul{display: block;position: absolute;width: 100px;}
.header_a:hover ul li:hover{background-color: #F5F5F5;}
.header_a ul li{color: #6c6c6c;height: 30px;line-height: 30px;text-align: left;padding: 0px 3px;margin: 5px 0px;}
/*现在时间紧，后面的再跟着课程来完善*/