I'm so impressed that this is your first game jam, and solo at that! It's got a surprising amount of polish and it's a ton of fun to play. The level design was spot on--each one upping the challenge or introducing a new concept. Nice work!
I would recommend a sound effect and a faster animation for when you successfully close a window. Since the window closing animation takes a second to play, it's tough to tell initially whether it registered. And it could make the act of successfully closing a window even more satisfying.