If you mean an image that repeats indefinitely, you would use the
background-repeat CSS property for that.
In this case, you would just take a singe-pixel vertical sliver of the background and use
background-repeat: repeat-x and layer that under the content background image. They're repeating at least three much larger background images and layering them to create the silver and red repeating areas off to the side though. That's a waste of bandwidth when they could be using single-pixel-wide images and merge some of them.
For every complex problem, there is an answer that is clear, simple, and wrong.