Mysterious dark box

This is the mysterious dark box you know why it got that name it is because when you shut the top of it would it would go dark, but when you opened it you would see that it would light up yellow. The reason it done that was because when you shut the lid it would go dark because the lid was blocking light from getting inside the box so then it would go dark. When the lid was open well you already know the box would light back up because the light was able to get in.