Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Writer/Xls/Workbook.php
private function writeStyle()
    {
        $record = 0x0293; // Record identifier
        $length = 0x0004; // Bytes to follow

        $ixfe = 0x8000; // Index to cell style XF
        $BuiltIn = 0x00; // Built-in style
        $iLevel = 0xff; // Outline style level

        $header = pack('vv', $record, $length);
        $data = pack('vCC', $ixfe, $BuiltIn, $iLevel);
        $this->append($header . $data);
    }
private function writeStyle()
    {
        $record = 0x0293; // Record identifier
        $length = 0x0004; // Bytes to follow

        $ixfe = 0x8000; // Index to cell style XF
        $BuiltIn = 0x00; // Built-in style
        $iLevel = 0xff; // Outline style level

        $header = pack('vv', $record, $length);
        $data = pack('vCC', $ixfe, $BuiltIn, $iLevel);
        $this->append($header . $data);
    }
Write Excel BIFF STYLE records.