Your skin1/skin1.css has the majority of the styles for your store for you to make background color changes or adding a border. You may also find main.css.
The template for the logo is skin1/rectangle_top.tpl and there are other templates that handle the copyright and prnotice. See the following post as a guide to find a template.
http://forum.x-cart.com/showthread.php?t=21529