public function offset($date = null): string
    {
        $offset  = $this->offsetInSeconds($date);
        $hours   = intval(abs($offset) / 3600);
        $minutes = (abs($offset)- ($hours * 3600)) / 60;
        return sprintf('%s%02d%02d', ($offset < 0 ? '-' : '+'), $hours, $minutes);
    }