Hi, thank you so much for this game.
A small suggestion - it would be nice if after clearing the board or running out of moves, there was a slight pause before the window pops up over the screen. This would give the user a chance to look at the board and see what boxes were left if they had lost, or to experience the satisfaction of a clear board if they had one.
Maybe there could be some sort of animation such as a flashing background while this is happening?