newbie trouble with theme loading

Hi
This is my first time on a forum…so thank you for any advice/help in advance…
I have spent hours trying to work out what I have done wrong….it is probably a simple mistake on my part….
I am using Matala theme on my blog. I thought I would have a play around with the header and background….now everything is just white. How can I undo this and bring back the lovely pattern background that comes with the Matala theme????