:visited is a pseudo class selector used for anchor link elements that matches when the href attribute of that anchor link has been visited in the past by this browser. It is meant to be useful feedback for a user, so they can tell the difference between links they have been to and links they have
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The :valid selector allows you to select <input> elements that do not contain valid content, as determined by its type attribute. :valid is defined in the CSS Selectors Level 3 spec as a “validity pseudo-selector”, meaning it is used to style interactive elements based on an evaluation of user input. This selector has one particular use: providing a user with feedback while they are interacting