Drupal 7: add user's role to the body class of the page

drupal7-add-user-role.php

<?php
function mytheme_responsive_preprocess_html(&$variables, $hook) {
  $body_classes = array($variables['classes_array']);

  // The body tag's classes are controlled by the $classes_array variable. To
  // remove a class from $classes_array, use array_diff().
  //$variables['classes_array'] = array_diff($variables['classes_array'], array('class-to-remove'));
  if ($variables['user']) {
    foreach ($variables['user']->roles as $key => $role) {
      $role_class = 'role-' . str_replace(' ', '-', $role);
      array_push($variables['classes_array'], $role_class);
    }
  }
}