8 CSS pseudo classes most likely you are not familiar with

:autofill

- The :autofill CSS pseudo-class matches when an <input> element has its value autofilled by the browser

See this in action here https://codepen.io/prathamkumar/pen/BapYOaz

:empty

- The :empty CSS pseudo-class represents any element that has no children.

:picture-in-picture

- The :picture-in-picture CSS pseudo-class matches the element which is currently in picture-in-picture mode.

For example, picture-in-picture mode of videos

:indeterminate

- The :indeterminate CSS pseudo-class represents any form element whose state is indeterminate, such as checkboxes which have their HTML indeterminate attribute set to true

:playing

- The :playing CSS pseudo-class selector is a resource state pseudo-class that will match an audio, video, or similar resource that is capable of being “played” or “paused”, when that element is “playing”.

:paused

Similarly, the :paused CSS pseudo-class selector is a resource state pseudo-class that will match an audio or video when that element is “paused”.

P.S. playing and paused are currenly is experiment. They are not standardized yet

:right

- The :right CSS pseudo-class, used with the @page at-rule, represents all right-hand pages of a printed document.

Similarly, :left pseudo-class for left-hand pages