A CSS pseudo-class is a keyword added to a selector that specifies a special state of the selected element(s). For example, the pseudo-class :hover can be used to select a button when a user's pointer hovers over the button and this selected button can then be styled.| MDN Web Docs
The :is() CSS pseudo-class function takes a selector list as its argument, and selects any element that can be selected by one of the selectors in that list. This is useful for writing large selectors in a more compact form.| MDN Web Docs
The :focus-visible pseudo-class applies while an element matches the :focus pseudo-class and the UA (User Agent) determines via heuristics that the focus should be made evident on the element. (Many browsers show a "focus ring" by default in this case.)| MDN Web Docs
The :not() CSS pseudo-class represents elements that do not match a list of selectors. Since it prevents specific items from being selected, it is known as the negation pseudo-class.| MDN Web Docs
1. Introduction| www.w3.org