Unfortunately this didn't work.
It looks like it opens a new document (theres a new document declaration half way down in this firebug screenshot)
I don't know if that is something to do with it. Even if I could just get rid of that corkboard background that is my default background image that'd make it easier to read.
This is the code I'm using for the other backgrounds:
#hikashop_category_information_menu_153, .hikashop_checkout_page, .hikashop_product_page,
.body-overlayed .contentpane{
position:relative;
background-image:url(../img/eggshell.jpg);
background-repeat:repeat;
width:680px;
padding:10px;
clear:left;
margin:10px 0 20px 0;
-webkit-box-shadow: 3px 3px 7px rgba(50, 50, 50, 0.7);
-moz-box-shadow: 3px 3px 7px rgba(50, 50, 50, 0.7);
box-shadow: 3px 3px 7px rgba(50, 50, 50, 0.7);
overflow:hidden;
}