interesting idea, the puzzles seem like they get quite complex unfortunately encountered a bug where if you try to place any cube in the red cube already on the grid it permanently deletes the cube you tried to place. I ended up with 0 cubes.
Whilst not a complaint for future reference I'd recommend having the cubes we can place appear at a side of the screen where we can drag them onto the grid with the mouse. Having to remember which number key corresponds to which cube is additional mind tax for an already taxing game.
But otherwise nice submission, the visual really fit the game and give it a unique stylistic feel