the shadows on the side of the window, creating a impression that the windows casts a shadow to its background. making people to believe that a distance exists between a windows and its background. later windows follow suit.
so much can be done with it. windows is the basic unit, the windows stacking is as much as it could have been. this fake 3d is reaching the end. ms windows 3.1 got it right. tiled windows are better. it could be better. 