Adding a class to the body tag in Drupal 8

Code snippet that can be used to add a class to the body tag in Drupal 8.

/**
 * @param $variables
 */
function mymodule_preprocess_html(&$variables)
{
    $node = \Drupal::routeMatch()->getParameter('node');
    if ($node) {
        $variables['attributes']['class'][] = 'page-' . $node->id();
    }
}

Example how to add a class to the body tag in specific node:

/**
 * @param $variables
 */
function THEMENAME_preprocess_html(&$variables)
{
    $node = \Drupal::routeMatch()->getParameter('node');
    if ($node instanceof \Drupal\node\NodeInterface) {
        if ($node->id() == 1 || $node->getType() == "article") {
            $variables['attributes']['class'][] = 'article-page-1';
        }
    }
}