Description

Developers would like to control more of the audio/video user experience. The :playing, :paused, :seeking, :buffering, :stalled, :muted, and :volume-locked CSS pseudo-classes match <audio> and <video> elements based on their state.

Specification

https://www.w3.org/TR/selectors-4/#resource-pseudos

WPT

css/selectors/media/media-loading-state.html
css/selectors/media/media-playback-state.html
css/selectors/media/sound-state.html

Additional Signals

Could be used by sites like Vimeo, YouTube, etc