This snippet adds the entity type id to the html body tag classes when on the canonical entity page.
/** * Implements hook_preprocess_HOOK() for HTML document templates. */ function yourtheme_preprocess_html(&$variables) { // If this is the canonical entity route, add the entity type id to the body // tag classes. Also add 'canonical' as an extra identifier. if (preg_match('/entity\.(\w+)\.canonical+/', Drupal::routeMatch()->getRouteName(), $matches)) { $variables['attributes']['class'][] = $matches[1]; $variables['attributes']['class'][] = 'canonical'; } }