Very well done and answered here – http://www.sitepoint.com/css3-transform-background-image/
#myelement:before {
content: "";
position: absolute;
width: 200%;
height: 200%;
top: -50%;
left: -50%;
z-index: -1;
background: url(background.png) 0 0 repeat;
transform: rotate(30deg);
}