Background Tiling

Evening all, I'm very new to the whole theme and how to css and have recently changed over to Catch Evolution Pro as I can have more hands on with the whole feel off it I have been trying to figure out how to make the background picture fit the screen it is being displayed on, I've got it fixed and like the way it sits there and they can scroll my info past please can you advise how to stretch the image peaceandlight.co.uk is my website Thank you Michael