Many content management systems that have a theme system which supports base (or parent) themes differ mostly in the terminology used. The concept of a base theme is used to provide established resources that are shared, reducing the amount of work required to create a new theme.

All libraries defined in the base theme will be inherited and used by default, allowing subthemes to reuse existing styles and JavaScript. This allows frontend developers to reuse their work and only create specific changes that are required for the subtheme.

The subthemes will also inherit all Twig template overrides provided by the base theme. This was one of the initiatives used for the creation of the Classy theme. Drupal 8 makes many fewer assumptions compared to the previous version as to what class names to provide on elements. Classy overrides all the core's templates and provides sensible default classes, giving themes the ability to use them and accept those class names or be given a blank slate.