Make your theme a subtheme of a "base" theme, allowing it to inherit all the base theme's templates and other properties. When creating Drupal themes it is common to use the Classy theme provided with Drupal core as a base theme to jumpstart your development.

In this article, we need understand:

• Use the base themekey in our theme's .info.yml file
• Make our Classical theme inherit from the Classy theme, or any other theme