Let’s talk about several selectors in CSS

Today this article mainly talks about several selectors in CSS. Friends who need it can refer to it. I hope it can help everyone.

1. Wildcard selector

The wildcard selector is represented by the "*" symbol. It has the widest scope among all selectors and can match the contents of the page. All elements

/*设置当前页面中所有标签的颜色为红色*/* {color: red;
}

2. Tag selector

The tag selector selects tags with the same name in the current page

/*设置所有p标签的文字颜色为红色*/p {color: red;
}

3. ID selector

The id selector is identified by "#", followed by the id name

{:;
}

This is the title

Note that the ID attribute value in the HTML tag must be unique in a page (it is a W3C specification rather than a hard rule).

ID selector naming convention

• Only letters (uppercase and lowercase, strict distinction), underscores, and numbers are allowed, that is to say, id="Head" Does not conflict with id="head"

• Only allowed to start with a letter

• There is no length limit for the name, it can be 1 letter, or There are many, but it is not recommended to be too long

• Tag names are not allowed (not a hard and fast rule)

4、类选择器

类选择器就是选取页面中所有标签的class属性值相同的一类标签，用.（点）表示 

{:;
}

这是标题1

这是标题2

 一个标签可以包含多个类选择器，在class标签中用空格隔开。

.head {color: blue;
}.subHead {font-size: 50px;
}

这是标题2

 5、复合选择器

5.1、交集选择器

交集选择器又称标签指定式选择器，由两个选择器构成，其中第一个为标记选择器，第二个为class选择器或id选择器，两个选择器之间不能有空格，如

h3.special  /* 需要满足标签是h3同时拥有special类 */

或

p#one /* 需要满足标签是p同时id为one */

 5.2、并集选择器

并集选择器是各个选择器通过逗号连接而成的，任何形式的选择器（包括标记选择器、class类选择器id选择器等），都可以作为并集选择器的一部分。如果某些选择器定义的样式完全相同，或部分相同，就可以利用并集选择器为它们定义相同的CSS样式

/*同时给标签h3与class为box的元素设置样式*/h3, .box {color: red;font-size: 14px;
}

 5.3、后代选择器

后代选择器用来选择元素或元素组的后代，其写法就是把外层标记写在前面，内层标记写在后面，中间用空格分隔。当标记发生嵌套时，内层标记就成为外层标记的后代（后代不仅仅包括儿子，还包括子子孙孙）。

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