Thanks, as stated in the main menu, the background is from opengameart.org - I can really recommend the site for Game Jams, many nice assets available.
Yeah, I overscoped a bit, that's why there is not much functionality besides a vs mode. My initial plan was to make you train an AI that fights the enemy AI for you, similar to Auto Pilot Games. But it took me way to much time to set everything up, and it turned out the AI support in Godot is kind of lacking.