drupal-reha/web/themes/custom/reha/reha.theme

<?php

/**
 * @file
 * Functions to support theming in the reha theme.
 */

/**
 * Implements hook_preprocess_HOOK() for html.html.twig.
 */
function reha_preprocess_html(&$variables) {
    $node = \Drupal::routeMatch()->getParameter('node');
    if ($node){
      $variables['attributes']['class'][] = 'node-type-' . $node->bundle();
      $variables['attributes']['class'][] = 'node-id-' . $node->id();
    }
}

/**
 * Implements hook_preprocess_HOOK() for page.html.twig.
 */
function reha_preprocess_page(&$variables) {

}

/**
 * Implements hook_preprocess_HOOK() for node.html.twig.
 */
function reha_preprocess_node(&$variables) {
    $node = &$variables['node'];
    $variables['attributes']['class'][] = 'node-type-' . $node->gettype();
}