How can I add a bg image to the outer background of my forum?

[Elektrisk]

OK, see how SF has this image as it's "outer bg" and green as its immediate bg (if you understand what I mean)?


How can I implement that into my forum? My image is:


But, in global.css, I see this image, which is my immediate bg:

Spoiler (Click to View)

This is the code:

Code:

body {
    background-image: url(images/brushed/background.jpg);
    color: #000;
    font-family: Verdana, Arial, Sans-Serif;
    font-size: 13px;
    text-align: center; /* IE 5 fix */
    line-height: 1.4;
}

Any idea?