When you drag no-drop over the yes-drop div it appears on top. If you then drag yes-drop and go back to dragging the no-drop this then appears under the yes-drop div.
Also I don't get what causes the highlight of the drop zones to activate. Percentage of shape? Center of Shape? Personally I prefer that it is the mouse pointer that activates the enter / leave and not the shape itself.
Added:
If you drag the yes-drop from the side to enter the drop zones, the outer zone looks like 50 pixels wide and yet the error or margin to drop it in there is about 2 pixels before you enter the inner zone.
When you drag no-drop over the yes-drop div it appears on top. If you then drag yes-drop and go back to dragging the no-drop this then appears under the yes-drop div.
Also I don't get what causes the highlight of the drop zones to activate. Percentage of shape? Center of Shape? Personally I prefer that it is the mouse pointer that activates the enter / leave and not the shape itself.
Added: If you drag the yes-drop from the side to enter the drop zones, the outer zone looks like 50 pixels wide and yet the error or margin to drop it in there is about 2 pixels before you enter the inner zone.