CSS selectors are used to target HTML elements for styling. Here are the main types:

1. Universal Selector (*): Selects all elements.
2. Type Selector: Targets specific elements, like all p tags.
3. Class Selector (.classname): Styles elements with a certain class.
4. ID Selector (#idname): Targets a unique element with an ID.
5. Attribute Selector: Styles elements based on attributes.
6. Descendant Selector: Selects elements inside another element.
7. Adjacent Sibling Selector (+): Selects the element right after another.
8. Pseudo-classes: Styles based on state, like :hover.
9. Pseudo-elements: Targets specific parts of an element.
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