TTG CE3 5.2.0 and newer automatically creates cart templates in a similar way to the creation of Publisher templates. To alter the customer-facing pages to the look-and-feel of your site, do the following:
1. Export a new gallery.
2. Copy the gallery into the cart/templates directory, e.g. cart/templates/my_template/
3. In the Cart Admin settings, change the Cart Template value to the name of your template directory, e.g. my_template.
4. Visit http://yoursite.com/cart/ to review that the change has taken effect without error.