You've asked. Steele has heard. Here is a technique for building a mythology for your very own story world. It's not the only way to build such a thing, of course, but considering it's been the foundation for over a dozen Starlight Runner clients, you might consider giving it a shot if you're struggling to codify your narrative universe!
Music - icons8.com, specifically https://icons8.com/music/author/ilya-marfin
Audio Effects - freesound.org