Thank you very much for composing this comment. It's very helpful and informative!
The background IS empty. I thought that placing more stars would fix it but it really didn't...
When the jam is finished I will fix both bugs especially the star upgrade, because you really need it
You are right sound in the shop would be nice
Concerning the theme, when I started making the game I had some more things in mind, but the result is not what I had planned :P