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// Add user role as a class to body

if ( is_user_logged_in() ) {
    add_filter('body_class','add_role_to_body');
    add_filter('admin_body_class','add_role_to_body');
}
function add_role_to_body($classes) {
    $current_user = new WP_User(get_current_user_id());
    $user_role = array_shift($current_user->roles);
    if (is_admin()) {
        $classes .= 'role-'. $user_role;
    } else {
        $classes[] = 'role-'. $user_role;
    }
    return $classes;
}