When mapping attributes, the GUI behavior is often quite irritating/buggy:

1. If I try to just drop an item at the right box, this doesn't work. I have to drop it ON TOP of the right box (same if you move an item back from right to left). This is irritating. Best solution: Let users drop the item anywhere at the huge right box. Alternative Solution: Show a section (rectangle) on top of the right box, maybe with some text "drop the next item here".

2. Can we change the background color to green once an item is placed at the correct place at the right box to indicate that the user can now drop the item and all is fine?

3. When moving an item back from right to left, the color doesn't change, it stays gray. Once dropped, the color should be white (background) again.