1. 浮动的元素会覆盖后面处于文档流中的元素
<html>
<head>
<style type="text/css">
.box-1{
float:left;
width:200px;
height:200px;
background-color:#333;
}
.box-2{
width:200px;
height:300px;
background-color:#ccc;
}
</style>
</head>
<body>
<div class="box-1"></div>
<div class="box-2"></div>
</body>
</html>
解决：只要给box-2(与浮动元素同级的元素)清除浮动就行了
<html>
<head>
<style type="text/css">
.box-1{
float:left;
width:200px;
height:200px;
background-color:#333;
}
.box-2{
width:200px;
height:300px;
background-color:#ccc;
clear:both;
}
</style>
</head>
<body>
<div class="box-1"></div>
<div class="box-2"></div>
</body>
</html>
2. 浮动元素会导致父元素高度坍塌
(1) 问题描述
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
(2) 问题分析
(3) 解决：解决思路主要是为父级清除浮动从而使父级div能获取到高度。
- 方案一（父级方法）：为父级div添加伪类after，并清除浮动
display:block;
content:"";
clear:both;
即：
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
/*清除浮动代码*/
.clearfloat:after{display:block;content:"";clear:both;}
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
- 方案二（子级方法）：在浮动的子元素尾部添加一个同级的空div标签或（br标签），并清除浮动
clear:both;
即：
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
/*清除浮动代码*/
.clearfloat{clear:both}
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
<div class="clearfloat"></div>
/*<br class="clearfloat" />*/
</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
- 方案三（父级方法）：为父级设置高度
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;height:200px;}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
- 方案四（父级方法）：为父级设置overflow：hidden
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;overflow:hidden}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
/*清除浮动代码*/
/*.clearfloat:after{display:block;content:"";clear:both;}*/
/*.clearfloat{clear:both}*/
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
- 方案五（父级方法）：为父级设置display:inline-block
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;display:inline-block}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
/*清除浮动代码*/
/*.clearfloat:after{display:block;content:"";clear:both;}*/
/*.clearfloat{clear:both}*/
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
- 方案六（父级方法）：为父级设置overflow:auto
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;overflow:auto;}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
/*清除浮动代码*/
/*.clearfloat:after{display:block;content:"";clear:both;}*/
/*.clearfloat{clear:both}*/
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
- 方案七（父级方法）：为父级设置display:table
<html>
<head>
<style type="text/css">
.div1{background:#000080;border:1px solid red;display:table;width:100%}
.div1 .left{float:left;width:20%;height:200px;background:#DDD}
.div1 .right{float:right;width:30%;height:80px;background:#DDD}
.div2{background:#800080;border:1px solid red;height:100px;margin-top:10px}
/*清除浮动代码*/
/*.clearfloat:after{display:block;content:"";clear:both;}*/
/*.clearfloat{clear:both}*/
</style>
</head>
<body>
<div class="div1 clearfloat">
<div class="left">Left浮动</div>
<div class="right">Right浮动</div>
</div>
</div>
<div class="div2">
div2
</div>
</body>
</html>
拓展：浮动布局多用于需要文字环绕的时候，毕竟这才是浮动真正的用武之地；水平排列可使用inline-block了，参考css之display:inline-block布局。
