"You must use all boxes!"

Why? If you can complete the level with less, why not?

I like this game a lot.

I partially agree with @GeoKureli below that it's mostly guessing. It's actually not, and there are several strategies, depending on the particular problem, but some trial-and-error is needed and that's hard to do the way the game is working now.

To make this part better, I would like to see "Undo" feature with checkpoints. Like, I rearrange the blocks, click "Set checkpoint", continue playing, make another checkpoint,... when I undo/redo, I go back to the previous/next checkpoint. IMO, this would make it much easier to try to solve each puzzle.

Another thing that would be nice to have: empty boxes outside to store unused blocks while working on a solution.

These are just wishes, but I'll go on playing it as it is. Nice, quick fun between more serious real-life tasks.

Fun mechanics, simplistic artstyle but charming. Puzzles are actually challenging and makes for great gameplay. Good work! Keep it up.

almost good!

Very nice game with a very good mechanics!