Selector

:first-child

The :checked selector matches every checked <input> element (only for radio buttons and checkboxes) and <option> element.

The :root selector matches the document's root element. In HTML, the root element is always the html element.

Specificity

inherits from its ancestor < Directly targeted elements . all the time

<span style="color:red;">	#text{color:red;}	.text{color:red;} [type="text"]{color:red}	span{color:red;}

x,0,0,0	0,x,0,0	0,0,x,0	0,0,0,x

!important 10000

1. Type selectors (e.g., h1) and pseudo-elements (e.g., ::before).
2. Class selectors (e.g., .example), attributes selectors (e.g., [type="radio"]) and pseudo-classes (e.g., :hover).
3. ID selectors (e.g., #example).

• 继承不如指定

• !important > 内联 > ID > Class|属性|伪类 Pseudo-classes | Pseudo-elements> 元素选择器

• :link、:visited、:hover、:active按照LVHA（LoVe HAte）顺序定义

Specificity Rules

• Equal specificity: the latest rule counts

• ID selectors have a higher specificity than attribute selectors

• Contextual selectors are more specific than a single element selector

• A class selector beats any number of element selectors

• The universal selector and inherited values have a specificity of 0

inline style > ID selector > class, attribute and pseudo-class selector > tag and pseudo-element selector