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CSS中的伪元素大家以前看过::first-line,:first-letter,:before,:after;

那么在CSS3中,他对伪元素进行了一定的调整,在以前的基础上增加了一个“:”也就是现在变成了::first-letter,::first-line,::before,::after另外他还增加了一个::selection。

在css3中,已经明确规定了伪类用一个冒号来表示,而伪元素则用两个冒号来表示。

::first-line选择元素的第一行,比如说改变每个段落的第一行文本的样式,我们就可以使用这个

p::first-line {font-weight:bold;}

::before和::after这两个主要用来给元素的前面或后面插入内容,这两个常用"content"配合使用,见过最多的就是清除浮动,

            .clearfix:before, .clearfix:after { content: "."; display: block; height: 0; visibility: hidden; } .clearfix:after {clear: both;} .clearfix {zoom: 1;}

对于 IE8 及更早版本中的 :before,必须声明 。

:before 选择器在被选元素的内容前面插入内容。例如:

<div> <h1 id="welcome">welcome</h1></div>div:before{ content:"hello world"}

那么,被选元素是div,div的内容是h1,插入的内容就是content属性值“hello world”

::selection用来改变浏览网页选中文的默认效果

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