I wasn't sure what to use for this and I think that's the point. Puzzle titles like Tetris, Pong, Breakout, and the like are very hard to define in terms of a Theme based on the choices available.
An Abstract Theme might be the best case in these situations.
AnimeCwboy shared this idea
Under Consideration · AdminIGDB (Admin, Twitch) responded
Hi! We talked about adding this theme, and we all agreed that it's a good idea. We just have to write clear guidelines around it. We are looking to add this as soon as possible. Thanks!