How to Change Background Colour to Background image

[ittybittykitty]

I feel real stupid for asking this question, because I know it's probably something simple, but I've googled my question a million times with no straight answer, and have been searching the forums for hours.

I just want to change the white back ground on my site (on the left and right outer sides) to a background image.

http://weddingprintdesign.com/

Ideally I would like it to look like the image below. So I need to know how to put it in and how to center it so the design stays on the outsides of the main page. (does that make sense?)

Hopefully I'm not way out in left field.

This is what I tried doing:

I went into the Stylesheet.css and typed

body {


margin: 0;


font-family: verdana, arial, helvetica, sans-serif;


font-size: 62.5%;


color: #3B3B39;


background-image: url("...image/back.jpg");


background-repeat: no-repeat;


background-position: left top;


}