设置了 .nav_mid_left,.nav_mid_right 属性，但是两个元素还是在同一列
如图所示：
HTML代码：
<!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>no title text</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"</div>
<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><!--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">5201314</span></div>
</div><!--logo结束-->
<div class="nav">
<div class="nav_left"></div>
<div class="nav_mid">
<div class="nav_mid_left"></div>
<ul>
<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>
</ul>
<div class="nav_mid_right">
<form action=""method="post">
<input type="text"/>
</form>
</div>
</div><!--nav_middle结束-->
<div class="nav_right"></div>
</div><!--nav结束-->
</div><!--wrap结束-->
</body>
</html>
CSS代码：
@charset "utf-8";
/* CSS Document */
*
{
margin: 0;
padding: 0;
font-size: 12px;
}
body
{
background-color: #F5F5F5;
}
/*.wrap
{
width: 1000px;
margin: 0 auto;
}*/
.top
{
width: 100%;
height: 27px;
background: url(../images/top_bg.jpg) repeat-x;
}
.top_content
{
width: 1000px;
margin: 0 auto;
}
.top_content li{
list-style-image: url(../images/li_bg.gif);
float: right;
width: 70px;
line-height: 27px;
}
.top_content a:link,.top_content a:visited{
color: #8E8E8E;
text-decoration: none;
}
.top_content a: hover,.top_content a:active{
color: #900;
text-decoration: none;
}
.wrap
{
width: 1000px;
margin: 0 auto;
clear: both;
}
.logo
{
height: 80px;
background-color: #FFF;
/*overflow: hidden;*/
}
.logo_left
{
width: 200px;
float: left;
}
.logo_right
{
width: 300px;
float: right;
height: 28px;
margin-top: 30px;
color: #8E8E8E;
}
.logo_right img
{
vertical-align: middle;
margin-right: 10px;
}
.tel
{
font-family: "微软雅黑";
font-size: 16px;
color: #C00;
}
.nav
{
height: 40px;
clear: both;
}
.nav_left
{
width: 10px;
background: url(../images/nav_left.jpg) no-repeat;
}
.nav_mid
{
width: 980px;
background: url(../images/nav_bg.jpg) repeat-x;
}
.nav_right
{
width: 10px;
background: url(../images/nav_right.jpg) no-repeat;
}
.nav_left,.nav_mid,.nav_right
{
float:left;
height:40px;
}
.nav_mid_left,.nav_mid_right
{
float:left;
}
.nav_mid_left
{
width:680px;
}
.nav_mid_right
{
width:300px;
}
