Summary of the three major features of CSS
#### 2.1 Inheritance
##### 2.1.1 Concept
A mechanism for passing attributes from parent elements to descendant elements.
##### 2.1.2. Performance
Descendant elements inherit the properties of the parent element.
##### 2.1.3. Summarize the common inheritable attributes
font-size、font-style、font-weight、font-family、font、text-align、text-indent、cursor、list-style等
##### 2.1.4, Mandatory inheritance
Every CSS property accepts these values inherit, indicating that inheritance is forced on".
##### 2.1.5 Function
Proper use of inheritance can simplify code and reduce the complexity of CSS styles.
#### 3.2. Priority
##### 3.2.1 Overview
The browser uses priority to determine which attribute values are most relevant to an element, and then apply these attribute values to the element.
Styles don't conflict, precedence doesn't make sense. Precedence only matters when there are multiple conflicting declarations for the same element.
##### 3.2.2 Inline styles and priority of selectors
Overview: Priority is based on matching rules composed of different types of selectors. A priority is a weight assigned to a given CSS declaration, determined by the value of each selector type in the matched selectors.
> Overview: The weight of the selector is expressed as 4 parts, such as 0, 0, 0, 0
The value of a selector is determined as follows:
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>(1) For each ID attribute value given in the selector, add 1, 0, 0, 0
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>(2) For each class attribute value, attribute selection or pseudo-class given in the selector, add 0, 0, 1, 0
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>(3) For each element and pseudo-element given in the selector, add 0, 0, 0, 1
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>(4) Associators and wildcard selectors do not contribute to specificity. Its specificity is 0,0,0,0
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>(5) The specificity of each inline declaration is 1, 0, 0, 0
**Summarize:**
The weight calculation method of a compound selector is: the weight accumulation of all the single selectors that make up it; the number of comparisons before the same level, and different levels cannot be crossed.
##### 3.2.3 Priority of inherited styles
Overview: Every CSS rule applied directly to an element always takes over/takes over the rules that the element inherits from its ancestors.