national holiday vs red letter day

national holiday

noun
  • A public holiday. 

  • A statutory holiday enacted by a country to commemorate the country itself. 

red letter day

noun
  • A particularly significant day; a day of personal or sectarian celebration. 

  • A day marked in red on calendars; a church feast day. 

How often have the words national holiday and red letter day occurred in a corpus of books? (source: Google Ngram Viewer )