css的定位机制:
普通流:浮动元素只能向左向右移动
浮动:浮动元素碰到包含框或者另一个浮动框会停止
绝对定位:浮动元素之后的元素将围绕它,之前不受浮动元素会脱离标准流
清除浮动的三种常用方法(一般用2, 3 ):
1 在浮动元素后使用一个空元素
eg:
<style>
.div1{ clear:both}
</style>
<div class="div1> </div>
2 给浮动元素的容器添加overflow:hidden
3 使用css3中的伪元素:(比较流行)
<style>
.clearfix :after{
content: "";
display: block;
height: 0;
visibility: hidden;
clear:both
}
.clearfix { zoom:1} 触发haslay out 兼容 IE 6 等浏览器
</style>
<div class="clearfix">
</div>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>mypractise</title>
<style>
*{ margin: 0;
padding:0
}
li{ list-style: none}
a{text-decoration: none}
.container{ width: 1200px; margin: 0 auto}
.header{ width: 1200px; background-color: #f2f2f2 ; overflow: hidden;zoom: 1}
.header .logo{ width: 100px; height: 80px; float: left}
.header .nav{float: right; overflow: hidden; zoom: 1}
.header .nav li{ float: left ; margin: 0 20px}
.header .nav li a { padding: 0 20px; display: block ; height: 80px; line-height: 80px; font-family: "宋体" ;font-size:15px }
.header .nav li a:hover{ color:white }
.main{ width: 1200px ; overflow: hidden; zoom: 1}
.main .left{ width: 900px ;height: 500px ;background-color: greenyellow;float: left}
.main .right{width: 300px ;height: 500px ;background-color:yellow;float: left}
.footer{ height: 200px ;width: 1200px;background-color: red }
</style>
</head>
<body>
<div class="container">
<div class="header">
<div class="logo">
<a href="#">
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</a>
</div>
<div class="nav">
<ul class="ul">
<li><a href="#">首页</a></li>
<li><a href="#">内容</a></li>
<li><a href="#">详情</a></li>
<li><a href="#">联系我们</a></li>
</ul>
</div>
</div>
<div class="main">
<div class="left">
left
</div>
<div class="right">
right
</div>
</div>
<div class="footer"> foot</div>
</div>
</div>
</body>
</html>