Which theme file should be edited when creating a preset for your theme?

When creating a preset for your Shopify theme, the settings_data.json file is the crucial element to consider. This JSON file stores the settings for the theme, including any specific configurations that can be customized in the theme editor. When you create a preset, you are essentially defining a set of default values and options that can be selected in the Shopify admin.

By editing the settings_data.json file, you can specify the various options available for your preset, such as colors, layouts, and typography. This allows for easy switching between different configurations without needing to manually change individual settings each time. Thus, modifications in this file ensure that the desired preset is properly registered and loaded into the theme editor, enabling users to apply the preset easily.

The other files serve different purposes: theme.liquid is primarily responsible for the overall structure of the theme's layout and content rendering; config.toml is used for configuration properties, typically for a simpler configuration format and does not directly relate to user-defined settings profiles; custom.css is meant for styling purposes and does not control preset configurations. Hence, the settings_data.json file is the correct choice for editing presets within a Shopify theme.