Hello!
Although LiteCommerce had a similar source code, it is not exactly the same.
In X-Cart 5 you have several ways to apply your changes to the design:
1. Use the "Custom CSS" & "Webmaster more" tabs on the Look & Feel page in the back-end
2. Enable Custom Skin module and put your changes there
3. Create a custom module and isolate your changes there
The 2nd and 3rd points assume that you know how to create modules for X-Cart 5. You can read more on this topic here:
http://kb.x-cart.com/