How do they get background image to span browser width?

Question

At http://www.archerschoicemedia.com, they have a background image at the top that spans the entire browser width. How is that achieved? What if image isn't as wide as screen resolution, won't it just repeat?
All help with adding a background image that does this - spans the entire browser width - is what I'm after.
Thanks!

Answer 1

What if image isn't as wide as screen resolution, won't it just repeat?
No.
The CSS reads
body {
font: 100% Verdana, Arial, Helvetica, sans-serif;
        background:url(../i/backgroundvid.jpg);
        background-position:center top;
        background-repeat:no-repeat;
        background-color:#000000;   
margin: 0; /* it's good practice to zero the margin and padding of the body element to account for differing browser defaults */
padding: 0;
text-align: center; /* this centers the container in IE 5* browsers. The text is then set to the left aligned default in the #container selector */
overflow-x: hidden;
overflow-y: auto;
So, the CSS is set to horizontally center the background image and not repeat it.
Plus, on screens wider than 1689px wide, the background color of black (#000000) shows through at the edges creating the impression that the background is endless.