Detailed graphic explanation of CSS basic clear float

Clear float

Box height problem

In the standard stream, the height of the content can support the height of the box

<style>

        div{
            background-color: red;
        }

        p{
            width: 200px;
            height: 100px;
            background-color: blue;
        }

</style>

<div>
    <p></p>
</div>

The height of the floating element content in the floating flow cannot support the height of the box

<style>
        div{
            background-color: red;
        }
        p{
            float: left;
            width: 200px;
            height: 100px;
            background-color: blue;
        }
</style>
<div>
    <p></p>
</div>

Clear floating method one

Add height to the previous parent box

Sample code:

<style>
 {
     margin: 0;
     padding: 0;
 }
 .box1{
     background-color: red;
     /这里*/
     height: 50px;
 }
 .box2{
     background-color: purple;
 }
 ul{
     list-style: none;
 }
 .ul01 li{
     background-color: blue;
 }
 .ul02 li{
     background-color: green;
 }
 ul li{
     float: left;
 }
</style>
<div class="box1">
   <ul class="ul01">
大娃

二娃

三娃

   </ul>

</div>

<div class="box2">

   <ul class="ul02">

李南江

极客江南

江哥

   </ul>

</div>

- Before adding height: - 

- After adding height - 

- Note: - In enterprise development, you can write height without writing it, so this method is not suitable. Commonly used methods for clearing floats 2 - Use the clear: both; attribute to clear the impact of previous floating elements on me

- Sample code: html

<style>
{
           margin: 0;
           padding: 0;
       }
       .box1{
           background-color: red;
       }
       .box2{
           background-color: purple;
           /这里/
           clear: both;
           /margin无效/
           margin-top: 30px;
       }
       ul{
           list-style: none;
       }
       .ul01 li{
           background-color: blue;
       }
       .ul02 li{
           background-color: green;
       }
       ul li{
           float: left;
       }
</style>
<div class="box1">
   <ul class="ul01">
大娃
二娃
三娃
   </ul>
</div>
<div class="box2">
   <ul class="ul02">
李南江
极客江南
江哥
   </ul>
</div>

- Add clear: both; Before: -  - After adding clear: both; - ! [](http://upload-images.jianshu.io/upload_images/647982-7b618617223102be.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240) - Notes: - Use margin after clear:both The attribute will be invalid, so it is not commonly used.

Clear float method three-Add an additional block-level element between two boxes with floating child elements

-Sample code: html

<style> 
       {
           margin: 0;
           padding: 0;
       }
       .box1{
           background-color: red;
       }
       .box2{
           background-color: purple;
       }
       ul{
           list-style: none;
       }
       .ul01 li{
           background-color: blue;
       }
       .ul02 li{
           background-color: green;
       }
       ul li{
           float: left;
       }
       /这里/
       .wall{
           clear: both;
       }
       .h20{
           /利用额外块级元素实现margin/
           height: 20px;
           background-color: deepskyblue;
       }
</style>
<div class="box1">
   <ul class="ul01">
大娃
二娃
三娃
   </ul>
</div>
<!--这里-->
<div class="wall h20"></div>
<div class="box2">
   <ul class="ul02">
李南江
极客江南
江哥
   </ul>
</div>

- Before adding additional block-level elements - 

- After adding additional block-level elements -  - Notes - In the exterior wall method, the margin effect can be achieved by setting the height of additional labels - Sohu uses this technology extensively, but due to the need to add a large number of meaningless labels, it is not commonly used `

Clear floating method 4 - Add an additional block-level element at the end of the previous box

- Sample code html

<style>
{
           margin: 0;
           padding: 0;
       }
       .box1{
           background-color: red;
       }
       .box2{
           background-color: purple;
           /margin有效/
           margin-top: 20px;
       }
       ul{
           list-style: none;
       }
       .ul01 li{
           background-color: blue;
       }
       .ul02 li{
           background-color: green;
       }
       ul li{
           float: left;
       }
       /这里*/
       .wall{
           clear: both;
       }
</style>
<div class="box1">
   <ul class="ul01">
大娃
二娃
三娃
   </ul>
   <!--这里-->
   <div class="wall"></div>
</div>


<div class="box2">
   <ul class="ul02">
李南江
极客江南
江哥
   </ul>
</div>- 添加额外块级元素前
    -  ![](http://upload-images.jianshu.io/upload_images/647982-37c3591032b43be9.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

- 添加额外块级元素后
    - ![](http://upload-images.jianshu.io/upload_images/647982-7799130801c08c6b.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

- Notes:
- The inner wall method will automatically support the height of the box, so you can directly set the margin attribute
- Like the inner wall method, you need to add a lot of meaningless empty labels, which violates the separation of structure and performance, and will be a nightmare in later maintenance.


Clear floating method five
- What is overflow:hidden?
- The function of overflow:hidden is to clear the content outside the border of the overflow box

- Sample code

```html
.test{
            width: 100px;
            height: 100px;
            border: 1px solid #000;
            background-color: red;
            overflow: hidden;
}

<div class="test">我是文字我是文字我是文字我是文字我是文字我是文字我是文字我是文字我是文字我是文字我是文字我是文字我是文字</div>

Before adding overflow:hidden

After adding overflow:hidden

How Use overflow:hidden; to clear the float

Add the overflow:hidden attribute to the previous box

###Sample code######

```html
<style>
     {
         margin: 0;
         padding: 0;
     }
     .box1{
         background-color: red;
         /这里/
         overflow: hidden;          zoom:1;
     }
     .box2{
         background-color: purple;
         /margin有效/
         margin-top: 20px;
     }
     ul{
         list-style: none;
     }
     .ul01 li{
         background-color: blue;
     }
     .ul02 li{
         background-color: green;
     }
     ul li{
         float: left;
     }
</style>
<div class="box1">
   <ul class="ul01">
大娃
二娃
三娃
   </ul>
</div>
<div class="box2">
   <ul class="ul02">
李南江
极客江南
江哥
   </ul>
</div>- 添加overflow:hidden;前
    - ![](http://upload-images.jianshu.io/upload_images/647982-37c3591032b43be9.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)


- 添加overflow:hidden;后
    - ![](http://upload-images.jianshu.io/upload_images/647982-7799130801c08c6b.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

- 注意点:
- 由于overflow:hidden可以撑起盒子的高度, 所以可以直接设置margin属性
- IE8以前不支持利用overflow:hidden来清除浮动, 所以需要加上一个*zoom:1;
- 实际上*zoom:1能够触发IE8之前IE浏览器的hasLayout机制
- 优点可以不用添加额外的标签又可以撑起父元素的高度, 缺点和定位结合在一起使用时会有冲突

- *zoom:1;和_zoom:1的区别
- 这个是hack写法，用来识别不同版本的IE浏览器
- _后面的属性只有IE6能识别
- *后面的属性 IE6 IE7能识别


###清除浮动方式六
- 给前面的盒子添加伪元素来清除浮动

- 示例代码

```html

<style>
        *{
            margin: 0;
            padding: 0;
        }
        .box1{
            background-color: red;
        }
        .box2{
            background-color: purple;
            /*margin有效*/
            margin-top: 20px;
        }
        ul{
            list-style: none;
        }
        .ul01 li{
            background-color: blue;
        }
        .ul02 li{
            background-color: green;
        }
        li{
            float: left;
        }

        /*这里*/
        .clearfix:after {
            /*生成内容作为最后一个元素*/
            content: "";
            /*使生成的元素以块级元素显示,占满剩余空间*/
            display: block;
            /*避免生成内容破坏原有布局的高度*/
            height: 0;
            /*使生成的内容不可见，并允许可能被生成内容盖住的内容可以进行点击和交互*/
            visibility: hidden;
            /*重点是这一句*/
            clear: both;
        }
        .clearfix {
            /*用于兼容IE, 触发IE hasLayout*/
            *zoom:1;
        }
</style>
<div class="box1 clearfix">
    <ul class="ul01">
        <li>大娃</li>
        <li>二娃</li>
        <li>三娃</li>
    </ul>
</div>
<div class="box2">
    <ul class="ul02">
        <li>李南江</li>
        <li>极客江南</li>
        <li>江哥</li>
    </ul>
</div>

添加伪元素前

添加伪元素后

注意点:

本质上和内墙法一样, 都是在前面一个盒子的最后添加一个额外的块级元素

添加伪元素后可以撑起盒子的高度, 所以可以直接设置margin属性

CSS中还有一个东西叫做伪类, 伪元素和伪类不是同一个东西

清除浮动方式七

给前面的盒子添加双伪元素来清除浮动

示例代码

<style>
        *{
            margin: 0;
            padding: 0;
        }
        .box1{
            background-color: red;
        }
        .box2{
            background-color: purple;
            /*margin有效*/
            margin-top: 20px;
        }
        ul{
            list-style: none;
        }
        .ul01 li{
            background-color: blue;
        }
        .ul02 li{
            background-color: green;
        }
        li{
            float: left;
        }

        /*这里*/
        .cf:before,.cf:after {
            content:"";
            display:table;
            /*重点是这一句*/
            clear:both;
        }
        .cf {
            zoom:1;
        }
</style>
<div class="box1 clearfix">
    <ul class="ul01">
        <li>大娃</li>
        <li>二娃</li>
        <li>三娃</li>
    </ul>
</div>
<div class="box2">
    <ul class="ul02">
        <li>李南江</li>
        <li>极客江南</li>
        <li>江哥</li>
    </ul>
</div>

添加双伪元素前

添加双伪元素后

注意点:

添加伪元素后可以撑起盒子的高度, 所以可以直接设置margin属性

先知道有这些方式, 原理需要学习到BFC和hasLayout才能明白

支持BFC的浏览器（IE8+，firefox，chrome，safari）通过创建新的BFC闭合浮动；

不支持 BFC的浏览器 （IE5-7），通过触发 hasLayout 闭合浮动。

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