Cornerstone
Cornerstone is a Drupal base theme that provides an advanced starting point for developers to create highly custom themes. It is designed for experienced themers and assumes a strong understanding of Sass/CSS, JavaScript, Twig, and Drupal theming concepts.
cornerstone [kawr-ner-stohn] something that is essential, indispensable, or basic: the chief foundation on which something is constructed or developed.
Cornerstone is a Drupal base theme designed for advanced Drupal themers. It provides a starting point for creating highly custom themes for companies and clients.
Because of its developer/advanced themer focus, it is not designed to be an out-of-the box turn-key theme. An advanced knowledge of Sass/CSS, JavaScript, Twig, and Drupal theming concepts, is assumed.