一、背景介绍
今天在解决一个当点击弹窗之后 整个背景应当是灰色的 界面 但是谷歌和IE浏览器 显示的背景不一致 所以 就有了下文........
解决之后的背景效果：
body.a-active::after{ content: ""; background-color: $ciot_black; opacity: 0.5; position: fixed; 100%; height: 100%; top: 0; }
二、介绍
css3为了区分伪类和伪元素，伪元素采用双冒号写法。
常见伪类——:hover,:link,:active,:target,:not(),:focus。
常见伪元素——::first-letter,::first-line,::before,::after,::selection。
::before和::after下特有的content，用于在css渲染中向元素逻辑上的头部或尾部添加内容。
这些添加不会出现在DOM中，不会改变文档内容，不可复制，仅仅是在css渲染层加入。
所以不要用:before或:after展示有实际意义的内容，尽量使用它们显示修饰性内容，例如图标。
举例：网站有些联系电话，希望在它们前加一个icon☎，就可以使用:before伪元素，如下：
<!DOCTYPE html> <meta charset="utf-8" /> <style type="text/css"> .phoneNumber::before { content:'260E'; font-size: 15px; } </style> <p class="phoneNumber">12345645654</p>
如下图所示：
三、content属性
::before和::after必须配合content属性来使用，content用来定义插入的内容，content必须有值，至少是空。默认情况下，伪类元素的display是默认值inline，可以通过设置display:block来改变其显示。
content可取以下值：
1、string
使用引号包一段字符串，将会向元素内容中添加字符串。如：a:after{content:""}
<!DOCTYPE html> <meta charset="utf-8" /> <style type="text/css"> p::before{ content: "《"; color: blue; } p::after{ content: "》"; color: blue; } </style> <p>平凡的世界</p>
效果如下：
2、attr()
通过attr()调用当前元素的属性，比如将图片alt提示文字或者链接的href地址显示出来。
<style type="text/css"> a::after{ content: "(" attr(href) ")"; } </style> <a href="http://www.cnblogs.com/starof">starof</a>
效果如下：
3、url()/uri()
用于引用媒体文件。
举例：“百度”前面给出一张图片，后面给出href属性。
<style> a::before{ content: url("https://www.baidu.com/img/baidu_jgylogo3.gif"); } a::after{ content:"("attr(href)")"; } a{ text-decoration: none; } </style> --------------------------- <body> <a href="http://www.baidu.com">百度</a> </body>
效果如下：
4、不使用图片创建小图标
举例：比如一个电话
很巧妙的应用一个div左border加圆角当机身，::before和::after配合圆角当听筒。
<style type="text/css"> #phone{width:50px;height:50px;border-left:6px solid #EEB422;border-radius:20%;transform:rotate(-30deg);-webkit-transform:rotate(-30deg);margin:20px;margin-right:0px;position:relative;display: inline-block;top: -5px;} #phone:before{width:15px;height:15px;background:#EEB422;border-radius: 20%;content: "";position: absolute;left:-2px;top: 1px;} #phone:after{width:15px;height:15px;background:#EEB422;border-radius: 20%;content: "";position: absolute;left:-3px;top: 34px;} </style> <div id="wraper"> <div id="phone"></div> </div>
效果如下：
更多的图标：
<!doctype html> <html> <head> <title>伪类标签使用</title> </head> <style type="text/css"> #wraper{padding:10px;width:380px;height:380px;border:3px solid #ccc;margin:auto;} #power{width: 30px;height: 30px;margin:20px;border: 6px solid #EEB422;border-radius: 50%;position: relative;display: inline-block;} #power:before{width:7px;height:22px;background:#EEB422;position: absolute;left:8px;top:-13px;content: "";border: 3px solid #fff;} #play{width: 30px;height: 30px;margin:20px;border: 6px solid #EEB422;border-radius: 50%;position:relative;display: inline-block;background: #EEB422;} #play:before{border:11px solid transparent;border-left:17px solid #fff;content: "";position: absolute;left:9px;top: 3px;} #pause{width: 30px;height: 30px;margin:20px;border: 6px solid #EEB422;border-radius: 50%;position:relative;display: inline-block;background: #EEB422;} #pause:before{height:20px;width:5px;border:0px solid transparent;border-left:8px solid #fff;border-right:8px solid #fff;content: "";position: absolute;left:4px;top: 5px;} #stop{width: 30px;height: 30px;margin:20px;border: 6px solid #EEB422;border-radius: 50%;position:relative;display: inline-block;background: #EEB422;} #stop:before{height:17px;width:17px;background:#fff;content: "";position: absolute;left:6px;top: 6px;} #comment{width: 50px;height: 25px;margin:20px;border: 6px solid #EEB422;border-radius: 20%;position:relative;display: inline-block;background: #EEB422;} #comment:before{border:10px solid transparent;border-top:10px solid #EEB422;content: "";position: absolute;left:28px;top: 28px;} #comment:after{content: "....";position: absolute;color: #fff;font-size: 26px;top: -10px;left: 2px;} #like{width: 50px;height: 30px;margin:20px;border-radius: 55%;transform:rotate(55deg);-webkit-transform:rotate(55deg);position:relative;display: inline-block;background: #EEB422;} #like:before{width:50px;height:30px;border-radius: 55%;transform:rotate(-110deg);-webkit-transform:rotate(-110deg);background:#EEB422;content: "";position: absolute;left:8px;top: -12px;} #search{width: 20px;height: 20px;border:4px solid #EEB422;border-radius:50%;margin:20px;position:relative;display: inline-block;top: -5px;left: -5px;} #search:before{width:20px;height:5px;background:#EEB422;transform:rotate(45deg);-webkit-transform:rotate(45deg);content: "";position: absolute;left:15px;top: 22px;} #home{width: 30px;height: 30px;background:#EEB422;margin:20px;position:relative;display: inline-block;top: 5px;} #home:before{width:6px;height:12px;background:#fff;content: "";position: absolute;left:12px;top: 20px;} #home:after{border:25px solid transparent;border-bottom:20px solid #EEB422;content: "";position: absolute;top: -38px;left:-10px;} #photo{width:40px;height:30px;background:#EEB422;margin:20px;position:relative;display: inline-block;top: 5px;} #photo:before{width:13px;height:13px;border:4px solid #fff;border-radius:50%;background:#EEB422;content: "";position: absolute;left:10px;top: 5px;} #photo:after{width:15px;height:10px;background:#EEB422;content: "";position: absolute;top: -7px;left:13px;} #photo{width:40px;height:30px;background:#EEB422;margin:20px;position:relative;display: inline-block;top: 5px;} #email{width:50px;height:35px;background:#EEB422;margin:20px;position:relative;display: inline-block;top: 5px;} #email:before{border:25px solid transparent;border-top:20px solid #fff;content: "";position: absolute;left:0px;top: 2px;} #email:after{border:25px solid transparent;border-top:20px solid #EEB422;content: "";position: absolute;top:0px;} #file{width:30px;height:45px;border:4px solid #EEB422;margin:20px;position:relative;display: inline-block;top: 5px;} #file:before{border:10px solid #fff;border-right:10px solid #EEB422;border-bottom:10px solid #EEB422;content: "";position: absolute;left:-4px;top: -4px;} #file:after{width:20px;height:5px;border-top:3px solid #EEB422;border-bottom:3px solid #EEB422;content: "";position: absolute;left: 5px;top: 25px;} #history{width:35px;height:35px;border:4px solid #EEB422;border-radius: 50%;margin:20px;position:relative;display: inline-block;top: 5px;} #history:before{width:14px;height:14px;border-bottom:4px solid #EEB422;border-left:4px solid #EEB422;content: "";position: absolute;left:14px;top: 3px;} #video{width:50px;height:35px;background:#EEB422;border-radius: 20%;margin:20px;position:relative;display: inline-block;top: -5px;} #video:before{width:6px;height:6px;border:11px solid transparent;border-right:11px solid #EEB422;content: "";position: absolute;left:35px;top: 4px;} #video:after{width:10px;height:10px;border:6px solid transparent;border-top:6px solid #EEB422;border-left:6px solid #EEB422;transform:rotate(45deg);-webkit-transform:rotate(45deg);content: "";position: absolute;left:13px;top: 35px;} #tags{width:50px;height:25px;background:#EEB422;border-radius: 35% 0% 0% 35%;transform:rotate(45deg);-webkit-transform:rotate(45deg);margin:20px;margin-left:35px;position:relative;display: inline-block;top: -5px;} #tags:before{width:10px;height:10px;border-radius:50%;background:#fff;content: "";position: absolute;left:7px;top: 7px;} #phone{width:50px;height:50px;border-left:6px solid #EEB422;border-radius:20%;transform:rotate(-30deg);-webkit-transform:rotate(-30deg);margin:20px;margin-right:0px;position:relative;display: inline-block;top: -5px;} #phone:before{width:15px;height:15px;background:#EEB422;border-radius: 20%;content: "";position: absolute;left:-2px;top: 1px;} #phone:after{width:15px;height:15px;background:#EEB422;border-radius: 20%;content: "";position: absolute;left:-3px;top: 34px;} #profile{width: 40px;height:15px;background:#EEB422;border-radius: 45% 45% 0 0;margin:20px;position:relative;display: inline-block;top: 0px;} #profile:before{width: 20px;height:22px;background:#EEB422;border-radius:40%;content: "";position: absolute;left: 10px;top: -22px;} </style> <body> <div id="wraper"> <div id="power"></div> <div id="play"></div> <div id="pause"></div> <div id="stop"></div> <div id="comment"></div> <div id="like"></div> <div id="search"></div> <div id="home"></div> <div id="photo"></div> <div id="email"></div> <div id="file"></div> <div id="history"></div> <div id="video"></div> <div id="tags"></div> <div id="phone"></div> <div id="profile"></div> </div> </body> </html>
效果如下：
6、给blockquote添加引号
经常用到给blockquote 引用段添加巨大的引号作为背景，可以用 ：:before 来代替 background 。好处是即可以给背景留下空间，还可以直接使用文字而非图片：
<meta charset="utf-8"/> <style type="text/css"> blockquote::before { content: open-quote; color: #ddd; z-index: -1; font-size:80px; } </style> <blockquote>引用一个段落,双引号用::before伪元素实现</blockquote>
效果如下：
7、超链接特效
举例：配合 CSS定位实现一个鼠标移上去，超链接出现方括号的效果
<meta charset="utf-8" /> <style type="text/css"> body{ background-color: #425a6c; } a { position: relative; display: inline-block; outline: none; color: #fff; text-decoration: none; font-size: 32px; padding: 5px 20px; } a:hover::before, a:hover::after { position: absolute; } a:hover::before { content: "5B"; left: -10px; } a:hover::after { content: "5D"; right: -10px; } </style> <a>鼠标移上去出现方括号</a>
8、::before和::after实现多背景图片
举例：一个标签应用5张背景图
<meta charset="utf-8" /> <style type="text/css"> #silverback { position: relative; z-index: 1; min-width: 200px; min-height: 200px; padding: 120px 200px 50px; background: #d3ff99 url(img/vines-back.png) -10% 0 repeat-x; } #silverback:before, #silverback:after { position: absolute; z-index: -1; top: 0; left: 0; right: 0; bottom: 0; padding-top: 100px; } #silverback:before { content: url(img/gorilla-1.png); padding-left: 3%; text-align: left; background: transparent url(img/vines-mid.png) 300% 0 repeat-x; } #silverback:after { content: url(img/gorilla-2.png); padding-right: 3%; text-align: right; background: transparent url(img/vines-front.png) 70% 0 repeat-x; } </style> <div id="silverback">一个标签应用了5张背景图片</div>
效果如下：
来源于：传送门