选择器的类型
<!doctype html><html><head> <meta charset="utf-8"> <title>css的选择器</title> <style type="text/css"> .stress{color:red;}/*类前面要加入一个英文圆点*/<br /> #setgreen{color:green} </style></head><body> <p>什么是<span class="stress">类选择器</span></p><br /> <p><span id="setgreen">id选择器</span>又是什么呢？</p></body></html> 类选择器在css样式编码中是最常用到的，如上图可以实现“类选择器”字体设置为红色。
.类选择器名称{css样式代码；} 英文圆点开头，其中类选择器名称可以任意起名不要用中文数字。
许多方面id选择器都类似域类选择符，但也有一些重要的区别：
1）为标签设置id="id名称"，而不是class=“类名称”
2）id选择器的前面是井（#）号，而不是英文圆点（.）
类和id选择器的区别：相同点 ：可以应用于任何元素
不同点：id选择器只能在文档中使用一次，可以拥有多个id但是id名称不能有冲突。 类选择器可以使用很多次。
可以使用类选择器词列表方法为一个元素设置多个样式。但只能用类选择器的方法实现。id选择器是不可以的。
<!doctype html><html><head> <meta charset="utf-8"> <title>子选择器..</title> <style type="text/css"> .food>li{border:1px solid red;}<br /> .first span{color:red;}<br /> *{font-size:20px;} </style></head><body> <p class="first">子选择器与<span>包含选择器</span></p> <ul class=" food" > <li>水果 <ul> <li>苹果</li> <li>香蕉</li> <li>橘子</li> </ul> </li> <li> <ul>蔬菜 <li>白菜</li> <li>青菜</li> <li>空心菜</li> </ul> </li> </ul></body></htmL> 如上，子选择器是用（>）大于符号，用于选择指定标签元素的第一代子元素。
.food>li{border:1px solid red;}<br />这行代码会使用class为food下的子元素li加入红色实线边框。<br />包含选择器，即加入空格，用于选择指定标签元素下的后辈元素，.first span{color:red;}<br />这行代码中“包含选择器”字体颜色变为红色。<br />子选择器是指他的直接后代，或者可以理解为作用于子元素的第一代后代，而包含选择器是用于所有子后代。包含选择器通过空格来进行选择，而子选择器通过>进行选择。<br />所以，>用于元素的第一代后代。空格用作于元素的所有后代。想试试效果的话把“.food>li”修改为“.food li”看看下效果把。<br /><br />*{font-size:20px;} 通用选择器。通用选择器是功能最强大的选择器，它使用一个（*）号指定，它的作用是匹配HTML中所有标签元素。
<!doctype html><html><head> <meta charset="utf-8"> <title>伪类选择器</title> <style type="text/css"> a:hover{ color:red; font-size:20px; } a#spe_a:hover{color:black;} .first，#second span{color:green;}<br /></style><br /></head><br /><body> <br /><br /> <h1 id="早晨九点的-a-href-链接地址-太阳-a-是最舒服的">早晨九点的<a href="链接地址">太阳</a>是最舒服的</h1> <p id="second">早晨八点是<span>上班上学</span>的<a id="spe_a" href="链接的地址">高峰期</p><br /></body></html><br /><br /> 什么是伪类选择器，它允许给html不存在的标签（标签的某种样式）设置样式，比如说我们给html中一个标签元素的鼠标滑过的状态来设置字体颜色与大小。<br />a:hover{color:red;font-size:20px}<br />上面一行代码就是a标签鼠标滑过的状态设置字体颜色变红，字体变大。但是这样是包含所有的a标签，如想让另一段不采用这样色彩可以改变它的。 <a id="spe_a" href="链接的地址"></a> a#spe_a:hover{color:black;}<br />这样就可以了，加id标签，在用a#加id地址在加上伪类选择器就ok了。 分组选择符<br />
.first，#second span{color:green;} 当你想为html中多个标签元素设置同一个样式时，可以使用分组选择器（，）上面代码表示.first标签第一段文字在用（，）连接”#second“在用空格连接span。这样第一段文字与id选择器中的span都是自己想要的文字效果了。
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