public static function solidBorder()
    {
        if (!self::$solidBorder) {
            self::$solidBorder = new static();
            self::$solidBorder->headerCellFormat = ' %s ';
            self::$solidBorder->cellFormat = ' %s ';
            self::$solidBorder->borderStyle = BorderStyle::solid();
        }

        return clone self::$solidBorder;
    }