Pretty good! Reminds me of some of the old Flash-based puzzle games.
The box was kind of janky: sometimes it would get stuck in the middle, and in the first puzzle it can get stuck on the right player’s head. Maybe for the first issue you could make the beam in the middle push the box out when the box crosses it, and for the second issue you could add platforms the player can walk into to push the box off.
I would have liked to see the window mechanic used more, to fit the limitation better.