Odd, it appears that your site has all of its pages (that I have looked at) mirrored from the dynamic Zen Cart page to a static HTML page, with URLs like
/shop/index6ac3.html?main_page=product_info&cPath=1&products_id=76
The same page (with very different styling) when accessed after viewing the shopping cart page is
/shop/index.php?main_page=product_info&cPath=1&products_id=76

I'm not sure what this means for your styling; the HTML page calls
includes/templates/clean_business/css/stylesheet.css
while the ZC page calls
includes/templates/avignon/css/stylesheet.css

Apparently ZC is set to the Avignon template, while the HTML pages reflect the use of the Clean Business template. You probably need to change the ZC template in Tools > Template Selection to Clean Business; I don't know if that will cause problems with any functional mods that may be active.