possible-body-classes.php

<?php

$route_name = \Drupal::routeMatch()->getRouteName();
$bits = explode('.', $route_name);
for ($i = 0; $i < count($bits); $i ++) {
  if ($i == 0) {
     $body_classes[] = str_replace('_', '-', $bits[$i]);                  
  }                       
  else {
     $body_classes[] = str_replace('_', '-', $bits[$i - 1] . '-' . $bits[$i]);                            
  }
}