深入理解CSS伪类_html/css_WEB-ITnose
× 目录 [1]锚点 [2]UI元素 [3]结构伪类 [4]其他
前面的话
伪类经常与伪元素混淆，伪元素的效果类似于通过添加一个实际的元素才能达到，而伪类的效果类似于通过添加一个实际的类来达到。实际上css3为了区分两者，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。本文将详细介绍伪类的详细知识
锚点
关于锚点，有常见的5个伪类，分别是:link,:hover,:active,:focus,:visited
a:link{background-color:pink;}/*品红，未访问*/
a:hover{background-color:lightblue;}/*浅蓝，鼠标悬停*/
a:active{background-color:lightgreen;}/*浅绿，正被点击*/
a:focus{background-color:lightgrey;}/*浅灰，拥有焦点*/
a:visited{color:orange;}/*字体颜色为橙色，已被访问*//*[注意]visited伪类只能设置字体颜色的样式*/伪类顺序
对于伪类顺序，有一个口诀是love-hate，代表着伪类的顺序是link、visited、focus、hover、active。但是否伪类的顺序只能如此呢？为什么是这个顺序呢？
CSS层叠中有一条法则十分重要，就是后面覆盖前面，所以伪类的顺序是需要精心考虑的。
【1】link和visited必须在最前面，且没有先后顺序，否则link或visited的效果将被覆盖
[注意]link和visited称为静态伪类，只能应用于超链接
【2】hover、active、focus这三个伪类必须是focus、hover、active的顺序，因为在focus状态下，也需要触发hover和active，而要触发active一定要先触发hover，所以active要放在hover后面
[注意]hover、active、focus称为动态伪类，可应用于任何元素，但IE7-浏览器不支持:focus，:hover和:active在IE6-浏览器下只支持给设置
所以最终的顺序只有两种:link、visited、focus、hover、active或visited、link、focus、hover、active
a:link{background-color:pink;}/*品红，未访问*/a:visited{color:orange;}/*字体颜色为橙色，已被访问*/a:focus{background-color:lightgrey;}/*浅灰，拥有焦点*/a:hover{background-color:lightblue;}/*浅蓝，鼠标悬停*/a:active{background-color:lightgreen;}/*浅绿，正被点击*/
UI元素伪类
UI元素伪类包括:enabled、:disabled、:checked三个，主要针对于HTML中的form元素，IE8-浏览器不支持
:enabled 可用状态:disabled 不可用状态:checked 选中状态
input:enabled{ border: 1px solid black; background-color: transparent;}input:disabled{ border: none; background-color: gray;}input:checked{ outline: 2px solid lightblue;}
<button onclick = "btn.disabled = false;">按钮可用</button><br /><button onclick = "btn.disabled = true;">按钮不可用</button><br /><input type="button" id="btn" value="按钮"><br /><br><label>Male<input type="radio" name="sex" /></label><br /><label>Female<input type="radio" name="sex" /></label>
[注意]input和:和enabled之间都不可以有空格
结构伪类
结构伪类可分为以下3种情况，IE8-浏览器不支持
//以下情况都是E为父元素，F为子元素
【1】:nth-child(n)、:nth-last-child(n)、first-child、last-child、:only-child
E F:nth-child(n) 选择父元素的第n个子元素E F:nth-last-child(n) 选择父元素的倒数第n个子元素E F:first-child 父元素的第一个子元素，与E F:nth-child(1)等同E F:last-child 父元素的最后一个子元素，与E F:nth-last-child(1)等同E F:only-child 选择父元素中只包含一个子元素
[注意]:firsr-child和:last-child只有IE6-浏览器不支持
n可以是整数(从1开始)，也可以是公式，也可以是关键字(even、odd)
p:first-child 代表的并不是<p>的第一个子元素，而是<p>元素是某元素的第一个子元素p > i:first-child 匹配所有<p>元素中的第一个<i>元素p:first-child i 匹配所有作为第一个子元素的<p>元素中的所有<i>元素
li:nth-child(odd){color: red;} li:nth-last-child(3){color: green;}li:first-child{color: blue;}li:last-child{color: yellow;}div:only-child{background-color:lightgrey;}
<ul> <li><div>第一个DIV</div></li> <li><div>第二个DIV</div></li> <li><div>第三个DIV</div></li> <li><div>第四个DIV</div></li> <li><div>第五个DIV</div></li> <li><div>第六个DIV</div></li> </ul>
【2】:nth-of-type(n)、:nth-last-of-type(n)、:first-of-type、:last-of-type、:only-of-type
E F:nth-of-type(n) 选择父元素的具有指定类型的第n个子元素E F:nth-last-of-type(n) 选择父元素的具有指定类型的倒数第n个子元素E F:first-of-type 选择父元素中具有指定类型的第1个子元素，与E F:nth-of-type(1)相同E F:last-of-type 选择父元素中具有指定类型的最后1个子元素，与E F:nth-last-of-type(1)相同E F:only-of-type 选择父元素中只包含一个同类型的子元素
.box div:nth-of-type(even){color: red;} .box p:nth-last-of-type(3){color: green;}.box div:first-of-type{color: blue;}.box p:last-of-type{color: yellow;}.box div:only-of-type{color: pink;}
<div class="box"> <div>第一个div</div> <p>第一个p</p> <div>第二个div</div> <p>第二个p</p> <div class="in">第三个div</div> <p>第三个p</p></div><div class="box"> <div>第四个div</div></div>
【3】:root、:not、:empty、:target
:root 选择文档的根元素，即<html>元素:not 选择除某个元素之外的所有元素:empty 选择没有子元素的元素，而且该元素也不包含任何文本节点:target 匹配锚点对应的目标元素
[注意]:not选择器只有safari9+及ios9.2+浏览器支持
:root{color:red;}div:not{background-color: lightgrey;}p:empty{height:30px;width:30px;background:pink;}:target{color:blue;}
<body> <a href="#test">测试</a> <div>第一个div</div> <p>第一个p</p> <div id="test">第二个div</div> <p>第二个p</p> <p></p> </body>
其他
【1】:lang() 匹配某个语言，IE7-浏览器不支持
p:lang(en) 匹配语言为"en"的<p>
【2】不仅可以使用单一伪类，也可以伪类结合使用
[注意]顺序无关
div:hover:first-child{background-color: lightgreen;}div:last-of-type:active{background-color: lightblue;}
<div>第一个div</div> <div>第二个div</div>
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