https://learn.microsoft.com/ja-jp/dotnet/api/system.timezoneinfo.baseutcoffset?view=netframework-4.8.1&viewFallbackFrom=net-9.0
TimeZoneInfo.BaseUtcOffset Property (System) | Microsoft Learn
Gets the time difference between the current time zone's standard time and Coordinated Universal Time (UTC).
property systemmicrosoftlearn