A theme can be enabled in Salesforce B2B Commerce in three different ways:

A Storefront setting: The theme can be specified in the Storefront Configuration settings in CCAdmin. This will apply the theme to all users who access the storefront.

An Account Group field value: The theme can be specified in the Theme field of an Account Group record in Salesforce. This will apply the theme to all users who belong to that account group.

Dynamically through a hook: The theme can be specified dynamically by extending the cc_hk_theme hook. This hook allows changing the theme based on various factors, such as the user, cart, product, or storefront. For example, the hook can apply a different theme for a specific product category or for a specific user segment.