At the moment the CSS rule that adds the custom background is this one:
Code:
body {
background-image: url(/var/theme/images/tweed.jpeg) !important;
}
Change it to:
Code:
html, body {
background-image: url(/var/theme/images/tweed.jpeg);
}
Also, you should tweak the image itself (at the moment it doesn't tile perfectly) and move it out of the "var" directory (XC5 may drop this directory and recreate it when rebuilding the site).