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css(层叠样式表  Cascading Style Sheet)-------表现层

目前最新版本CSS3.0,能够做到表现与内容分离的一种计算机语言,在css中主要学习选择器和属性

在学习之前先看一下css的书写位置和需要注意的地方

书写位置

    1、外联(外部)样式  

    2、嵌入(内页)样式  

    3、内部(行内)样式  

书写格式

选择器{属性:属性值}

注意:在CSS中多个属性用分号隔开

   注释方法为/*注释内容*/

选择器

  基础选择器

    *选择器    表示获取html文档中所有的标签,一般用在统配(全局)样式

    html选择器(标签选择器)   标签名{}

   类选择器   .类名{}

    ID选择器   #ID值{}

关系选择器

    E F(后代选择器)  E元素下边的F元素

    E>F (子集选择器)   E元素的子集元素F

    E+F (紧邻选择器) 紧邻E元素之后的兄弟元素F

    E~F (兄弟元素选择器) 选择E元素的兄弟元素F

属性选择器

    E[attr]   具有attr属性的元素E

    E[attr="value"] 具有attr属性的并且其属性值等于value的元素E 

    E[arrr^="value"] 具有attr属性的并且其属性值以value开始的元素E

    E[attr$="value"]  具有attr属性的并且其属性值以value结尾的元素E

    E[attr*="value"]   具有attr属性的并且其属性中包含value的E元素

伪类选择器

       :active   当元素在被激活的时候时的样式

       :link    a标签未被访问前的样式

       :visited  a标签已被访问过得样式

       :hover    鼠标滑过的样式

伪对象选择器

    E::before{content:"123";}   在E元素之前常与content属性配合使用

    E::after{content:"abc";}    在E元素之后常与content属性配合使用

    E::first-letter{color:red;}  E元素内容的第一个字符

    E::first-line{color:red;}    E元素内容的第一行

    


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