background image moves with width

On http://blog08.net, my background images resizes itself when you shorten the browser window. I know it’s a small fix but I don’t seem to find the problem.

My style.css looks as following:

body {
background: #FFFFFF url(http://www.blog08.net/images/content.jpg) top center repeat-y;
color: #333333;
font-size: 11px;
font-family: Verdana, Helvetica, Sans-Serif;
margin: 0px auto 0px;
padding: 0px;
}