I am aware, this is a prototype for a concept, I failed to find a no-copyright music for it. Would appreciate if you know a good source
I went with no music at all, but it was kinda reasonable for my game(even though comments beg to differ :) ) Gamedev youtubers often point out to free online midi sequencers, so you can try to throw some notes to board and choose instruments that sound appropriately for game.
Something like that one: https://onlinesequencer.net/