Like i told you in on of your other topics on this.
(You should only open one topic for the same topic )
Change "top edge" property of anchor bavior of your button to "Window Bottom".
I attached your fixed capx. (note: didnt change anything else than this).
Edit: Okay i just saw its about the background.
For this try to go with 960, 640 layoutsize.
Also having one big backgroundimage wont be working for this at all, since the screen would never adapt to the image or it would start to repeat.
In your case split your image into parts. Have the green to the left positioned at ViewportLeft and the other at ViewportRight.