Help editing CSS code

I need help finding the CSS code that controls the background color of the product windows on the product page. I am using firebug and found the code that makes the change but I can't find the CSS document to make the change.

#hikashop_category_information_menu_158 div.hikashop_subcontainer {
background-attachment: scroll;
background-clip: border-box;
background-color: #FFFFFF; <–––––––( I want to change this!)
background-image: none;
background-origin: padding-box;
background-position: 0 0;
background-repeat: repeat;
background-size: auto auto;

The domain is thekoipond.com/index.php/t

Hi,

First you can modify the CSS file directly in HikaShop in order to add rules.
www.hikashop.com/en/support/documentation/faq.html#css

After that, your menu (with id 158) have some options configured that you can changed in the backend in: HikaShop > Content Menu
By editing the menu with the id 158, you would found the appropriated color option.

Regards,