// Add user ID to admin body class
function add_user_id_to_admin_body_class($classes) {
    // Get the current user ID
    $current_user_id = get_current_user_id();

    // Append the user ID as a class
    if ($current_user_id) {
        $classes .= ' user-id-' . $current_user_id;
    }

    return $classes;
}
add_filter('admin_body_class', 'add_user_id_to_admin_body_class');