Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 26 Maundy Thursday
March 27 Good Friday
March 29 Easter
March 30 Easter Monday
May 01 International Workers' day
May 07 Feast of the Ascension
May 17 Constitution Day
May 18 Pentecost Monday
December 25 Christmas
December 26 St Stephen's Day
DateTimeExtensions DateTimeExtensions