I don’t really see much challenge here. Just draw some simple lines indicating an apt below, and you’re done. It just means the lights are on down there, which is a reasonable take given that the implied joke is that the piano crushed someone.

Or if you want to get ‘fancy,’ Larson already has some hatching lines on the side of the TV and the building opposite. Just use something like that. Literally any of those things would have looked more natural than the ‘starfield,’ altho I must confess I kind of like it just because it looks so out of place!