As an FYI, the text file is a list of the days of the year day1- Jan 1... day 365 - Dec 31. like Holidays imported from Calendar > Add Holidays, they are individual events, 1 a day for 365 days.
For more fun with this, a HOL file with the day numbers and days to go. Download, remove the .txt from the file, double click to run - it will bring up the Add Holidays dialog. By using a HOL file, the events are in the holiday category.
View attachment DayNumbers.HOL.txt
The CSV has advantages - you can add a Category column and put them into their own category. That maks it easier to hide or delete them.