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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