since you have a great break point on the wall on the left,

I would paint the whole corner and the right side wall (the door opening wall) Dark,

I would choose Navy SW Naval, but BM Black Forest Green would be dramatic as well.

Paint the wall and shelf all the same color. I personally would add a shelf triangle to join the unit and offer a useful surface for a soundbar, etc.

Thanks @Lyn! Would you paint the whole right side wall? Or just up to the opening?

@Monica B the whole right side wall. ...now that I see the next room, I'd paint the outside stairwall White, to brighten that space and show off that tile floor.

even a dramatic piece of stained glass for that little window?