1. Inline style refers to the style defined in the html document
<h1 style="color: #fff;">headerh1>
2. ID selector
3. Class, attribute selector and pseudo-class selector
This category includes various classes, attribute selectors, pseudo-class selectors such as :hover, :focus, etc.
4. Elements and pseudo-elements
Element and pseudo-element selectors, such as :before and :after.
Pseudo element:
Start from 0, an inline style +1000, an id +100, an attribute selector/class or pseudo-class +10, an element name, or pseudo-element +1