CSS `:fullscreen` is not applicable to the map element(s)

[Malvoz]

Currently, it is the .leaflet-container that goes into fullscreen mode when activating fullscreen, which means it isn't possible to change e.g. background-color of the map element using the :fullscreen pseudo class on web-map/mapml-viewer.

I'd say this is low priority, but is unfortunate, authors would expect this to work on a native element.