The appearance of your store is defined by the theme. The theme includes the visual style as well as all the functions in the store. By customizing the theme's source code, you can adjust the appearance and functionality to your liking.
You can find the source code in Online Store > Edit Theme > Theme > Source Code.
Clicking Source Code opens a code editor, allowing you to modify the code and add or remove files.
Find detailed theme documentation for developers.
Never Customize the Source Code of a Published Theme
Only edit the source code of a theme or theme version that is not published. Editing the source code can cause serious functionality issues in the store, so never edit the code of a theme that is live in the store.
When you want to customize a theme currently in use, first make a copy of the theme and customize that version. Once the modifications are complete and the theme’s functionality has been thoroughly tested, publish it for use in the store.