Just a sample site of a possible usage of DateTimeExtensions nuget package.
January 01 New Year
March 25 Maundy Thursday
March 26 Good Friday
March 28 Easter
March 29 Easter Monday
May 01 International Workers' day
May 06 Feast of the Ascension
May 16 Pentecost
May 17 Constitution Day
December 25 Christmas
December 26 St Stephen's Day
DateTimeExtensions DateTimeExtensions