When custom and contributed themes are added to a fresh Drupal installation, the core themes often fade into the background, even though they are valuable, particularly for learning theming. In Drupal 7, those core themes are: Bartik (enabled by default), Garland (Drupal 6's default), Seven (optimized for site administration), and Stark (minimalist and thus useful for module output debugging). The sole template engine is the venerable PHPTemplate. Drupal 8 adds Twig as the canonical template engine. Garland is gone, while Bartik, Seven, and Stark have been HTML5-ified and Twig-ified.