The idea is clever and the game is very intuitive from the get go. Simple rules, complex solutions for the puzzles. I basically liked everything about this game, even the sound fits well with the aestetics.
Minor criticism: "R" to me feels more intuitive for the restart button, and I also would've put a "restart" textbutton when you lose, I ended up on the level selection section many times just because I wanted to restart (and then i remembered about "X").
You could really expand this, good job!