为啥我的list_main页面浮动出错了呢
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<link href="css/main.css" rel="stylesheet" type="text/css"/>
<script src="js/setHomeSetFav.js" type="text/javascript" charset="gb2312"></script>
</head>
<body>
<div class="top">
<div class="top_content">
<ul>
<li><a href="#">联系我们</a></li>
<li><a href="#" onclick="AddFavorite(window.location,document.title)">加入收藏</a></li>
<li><a href="#" onclick="SetHome(window.location)">设为首页</a></li>
</ul>
</div>
</div><!--top结束-->
<div class="wrap">
<div class="logo">
<div class="logo_left">
<img src="images/logo.jpg" alt="慕课网"/>
</div>
<div class="logo_right">
<img src="images/tel.jpg" alt="服务热线"/>
24小时服务热线：<span class="tel">123-456-7890</span>
</div>
</div><!--logo结束-->
<div class="nav">
<div class="nav_left"></div>
<div class="nav_mid">
<div class="nav_mid_left">
<li><a href="#">首页</a></li>
<li><a href="list.html">关于慕课</a></li>
<li><a href="list.html">新闻动态</a></li>
<li><a href="list.html">课程中心</a></li>
<li><a href="list.html">在线课程</a></li>
<li><a href="list.html">人才招聘</a></li>
</div>
<div class="nav_mid_right">
<form action="" method="post">
<input type="text"/ class="search_text">
</form>
</div>
</div>
<div class="nav_right"></div>
</div><!--nav结束-->
<div class="ad" id="picBox" style="height:243px">
<img src="images/ad.jpg" />
</div>
</div><!--ad结束-->
<div class="list_main">
<div class="news_type"></div>
<div class="list_box"></div>
</div>
</div><!--wrap结束-->
<div class="copyright">
<div class="copyright_content">
<ul>
<li><a href="#">关于</a>
<ul>
<li>品牌故事</li>
<li>联系我们</li>
<li>加入我们</li>
<li>版权声明</li>
</ul>
</li>
<li><a href="#">课程</a>
<ul>
<li>PHP开发</li>
<li>前端开发</li>
<li>JAVA开发</li>
<li>Android开发</li>
</ul>
</li>
<li><a href="#">留言</a>
<ul>
<li>新浪微博</li>
<li>腾讯微博</li>
<li>企业微信</li>
<li>QQ空间</li>
</ul>
</li>
<li><a href="#">关注</a>
<ul>
<li>意见反馈</li>
<li>问题留言</li>
<li>媒体联络</li>
<li>在线客服</li>
</ul>
</li>
<li><a href="#"><img src="images/weixin.png"/ alt="微信关注" width="30" height="27">微信关注</a>
<ul><li><img src="images/qrcode.jpg"/ alt="扫描关注慕课网官方微信" width="102" height="102"></li></ul>
</li>
</ul>
</div>
</div>
</body>
</html>
