The :stalled CSS pseudo-class selector represents an element that is playable, such as <audio> or <video>, when playback is stalled. A resource is considered to be stalled if the user has requested playback of a specific position in the media resource, but it has failed to receive any data for some amount of time. This is different from :buffering in that the media element is unexpectedly not loading data when stalled (e.g. due to a network error) for around 3 seconds (the exact time is user agent dependent).
Note: Like with the :buffering pseudo-class, the element is still considered to be "playing" when it is "stalled". If :stalled matches an element, :playing will also match that element.