Sub-theming

In Drupal, sub-theming refers to the process of creating a new theme that inherits and extends the functionality of an existing base theme. It allows you to customize the appearance and behavior of your Drupal site without modifying the base theme directly. Sub-theming is a powerful technique that enables you to build unique designs while benefiting from the updates and improvements made to the base theme.

The inheritance chain follows a linear path, and each theme can only have one parent theme. The visible markup presented to the user on a page is the outcome of how each theme in this chain modifies the markup received from the preceding theme, with the active theme having the ultimate authority in determining the final markup.

Imagine, for example, that our Alps Trips company became successful, and we opened a French office to manage tours in the French Alps. We want a site with the same content types and configuration but with some differences on the frontend...