I am in love with this game... Really well done on every front, this was super fun!
I know exactly how hard it is to make puzzle games, especially designing levels can get really stressful, this is no easy feat! I liked all the levels and I think the difficulty was fair but it got easier toward the end for me.
Also I think I stumbled upon a bug. When you get an answer wrong or leave a blank space, the no state could be determined message appears, which makes sense. The issue is that the game then occasionally locks some of the kitties, preventing you from changing them unless you reset the level? It's hard to explain. It feels like the answer detection is slightly bugged.
Also having the kitties popping out to fill the screen is super cute! They do hinder UI visibility at times, though, My suggestion would be to make them a little transparent or something, so they don't distract you from the puzzle.
Overall though very very very well done!! I love this!