A valid CSS pseudo-class is a keyword that enables styling HTML elements based on their state or position in the document structure or webpage.

Web developers use CSS (Cascading Style Sheets) to modify an HTML element's appearance. A valid CSS pseudo-class adheres to CSS syntax rules and standards, ensuring proper and error-free formatting, which allows browsers to interpret it correctly.

A pseudo-class is a label that comes after a colon symbol (:). Web developers attach pseudo-classes to HTML elements, allowing them to apply desired styles based on certain characteristics, conditions, and user interactions.

For example, by leveraging the :hover pseudo-class, developers can style an element’s appearance — such as an image or a button — altering its behavior when a user hovers over it.

By enhancing the customization of specific elements, valid CSS pseudo-classes contribute to a website’s responsiveness and user-friendly design.

Visit Webflow University for an overview of CSS layout and positioning.

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