Overview
Znode Storefront themes are located under the "/Themes" folder. Here's the screenshot of the folder structure:

Modifying the theme

• Znode Storefront comes with a default theme. This theme is located under the "\Themes\Default" folder
• The CSS stylesheet is located at "\Themes\Default\style.css" - Use the stylesheet to modify global styles for the storefront
• Znode Storefront has a Main Master page that can be found at "Themes\Default\Common\Main.master". All other master pages inherit from this master. This master page defines common elements for the site such as header, footer, etc

Modifying pages

• Each functionality in the storefront is categorized under separate folders that are located under "\Themes\Default\"
• For example: To modify the product detail pages, modify the Product.master page located under "\Themes\Default\Product" folder.  

Creating your own theme
You can create your own themes under the Themes folder. For example, copy the "\Themes\Default" folder (and all subfolders) to "\Themes\MyTheme" folder to create your theme called "MyTheme". Note that you would then need to select this new theme using the Storefront Administration > Store Settings page