There's an autosave option in the game, but if you want to use savefiles, there's an "Import savefile" button when clicking "Play" in the Main Menu. Note that this option is only visible under an empty slot, so make sure to have at least one available!
Hello! Sadly, that theme was bought from a royalty-free songs bank. Royalty free tracks tend to have very generic names (the name of this one was "Lo-Fi Guitar" or something like that) so they're very hard to track down.
Hello! For WebGL, controller is not recommended as Unity is not optimized for WebGL games and bugs like these might happen. Or does it happen in the Windows build?