danland css for setting JPG as background image

Hi
please help a newbie solve this please please please please please please

i have a danalnd theme installed
it's working fine
i have created a bit of css to put a jpg as a background in style.css
body {
background:url("/sites/images/background/background-image-1000.jpg") repeat;
font-size: 84%;
font-family: Arial, Helvetica, sans-serif;
color: #000;
margin: 0;
padding: 0;
line-height: 1.5em;
}

on the page there are sthe slider image, a panel page and menus.
what i want is to set the background to the page to be white
so the background in style.css only appears at the side

i know i should add something like
background-color: white;

but where i put this

i want the main page to be about 960px wide.
anything outside of this should be the bacground image in style.css

hope this is clear

please help

belial