html coding for website to make image repeat behind it on both sides

[Sherwood]

Hi I've spent ages trying to figure out the html coding myself, plus asking other people and searching on the net and i can't figure out how to do this so it's driving me crazy. Basically if you just click on this girls website- yxyv.tumblr.com i really want to know what the html coding is so that the image is in the middle and then it's manipulated around on both sides behind it. i really can't figure it out and it's driving me crazy, if someone could help me i would be unbelievably grateful