It's easy. Just go to your tpl_shopping_cart_default.php (includes/templates/yourtemplate/templates) page and before the <table> tabe put in a <div> tag. Then go down to below the final </div> tag and put in another closing </div> tag. Set a class to it, and define the class in your css file. Upload it, and you're ready to go! PM me if you need more help.