A CSS pseudo-class is a keyword added to a selector that lets you select elements based on information that lies outside of the document tree, such as a specific state of the selected element(s). For example, the pseudo-class :hover can be used to style a button when a user's pointer hovers over it.
CSS selectors - CSS | MDN
The CSS selectors module defines the patterns to select elements to which a set of CSS rules are then applied along with their specificity. The CSS selectors module provides us with more than 60 selectors and five combinators. Other modules provide additional pseudo-class selectors and pseudo-elements.
element() CSS function - CSS | MDN
The element() CSS function defines an <image> value generated from an arbitrary HTML element. This image is live, meaning that if the HTML element is changed, the CSS properties using the resulting value are automatically updated.
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Side-by-side comparisons of outdated CSS techniques and their modern native replacements. Grid, custom properties, nesting, container queries, and more.
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