Theme Inheritance with Base Themes for Drupal 8, 9, and 10

Custom themes in Drupal must be configured to inherit settings, templates, and other assets from a parent theme. Which base theme you use is configurable. This allows theme developers to use a different set of markup as the starting point for their theme, organize various theme assets into a more maintainable structure, and more. All of this is made possible because of how Drupal's theme layer uses a chain of inheritance when assembling all the parts of a theme.

Base themes are also a powerful way to encapsulate standards and best practices into a reusable code base. You'll find dozens of contributed base themes on that can serve as a great starting point, especially if you're planning to work with an existing design framework like Bootstrap or Susy Grids. Or if you want to leverage modern JavaScript bundling without setting up Webpack on your own.

In this tutorial we'll:

  • Learn what base themes and subthemes are
  • Look at a few examples of template inheritance and how that works
  • Discuss some use cases for theme inheritance

By the end of this tutorial you'll know how to declare the base theme that your theme builds upon.

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