CSS 4.2.4参考手册
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©
本文档使用 php.cn手册 发布

文字

语法：

E:before/E::before { sRules }

说明：

设置在对象前（依据对象树的逻辑结构）发生的内容。用来和content属性一起使用，并且必须定义content属性

  • CSS3将伪对象选择符(Pseudo-Element Selectors)前面的单个冒号(:)修改为双冒号(::)用以区别伪类选择符(Pseudo-Classes Selectors)，但以前的写法仍然有效。

    即E:before可转化为E::before

兼容性：

SelectorIEFirefoxChromeSafariOperaiOS SafariAndroid BrowserAndroid Chrome
Basic Support6.0-7.02.0-3.0 #24.0+3.1+15.0+3.2+2.1+18.0+
8.0+3.5+
::before6.0-7.02.0-3.0 #2
8.0 #13.5+
9.0+
应用动画6.0-9.02.0-3.54.0-25.03.1-6.015.0+3.2-6.12.1-3.018.0-25.0
10.0+ #34.0+26.0+6.1+7.0+4.0+26.0+

  1. 本质上并不支持伪元素的双冒号(::)写法，而是忽略掉了其中的一个冒号，仍以单冒号来解析，所以等同变相支持了E::before。

  2. 不支持设置属性position, float, list-style-*和一些display值，Firefox3.5开始取消这些限制。

  3. IE10在使用伪元素动画有一个问题：

    例如：

    .test:hover {} .test:hover::before { /* 这时animation和transition才生效 */ }

    需要使用一个空的:hover来激活

示例：

实例

<!DOCTYPE html>
<html lang="zh-cmn-Hans">
<head>
<meta charset="utf-8" />
<title>E::before_CSS参考手册_web前端开发参考手册系列</title>
<meta name="author" content="Joy Du(飘零雾雨), dooyoe@gmail.com, www.doyoe.com" />
<style>
p{position:relative;color:#f00;font-size:14px;font-size:0\9;*font-size:14px;}
p:before{position:absolute;background:#fff;color:#000;content:"如果你的能看到这段文字，说明你的浏览器只支持E:before";font-size:14px;}
p::before{position:absolute;background:#fff;color:#000;content:"如果你的能看到这段文字，说明你的浏览器支持E:before和E::before";font-size:14px;}
</style>
</head>
<body>
<p>Sorry, 你的浏览器不支持E:before和E::before</p>
</body>
</html>

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