A forgotten tradition: the fasting day before Christmas.
Until 1958, Catholics generally fasted on December 24; it was a one-day fast in preparation for Christmas. It had remained even as various customs of fasting and / or abstinence on some days of Advent vanished through the centuries.
In 1959, Pope John XXIII permitted (but did not require) the fast to be moved to December 23. Even before 1959 some countries already had this permission. Pope John XXIII made it universal.
The obligation to fast on either December 23 or December 24 was removed by the Apostolic Constitution "Paenitemini" (1966).
Nevertheless there is nothing wrong in voluntarily observing this one day of fasting, especially as an act of prayer and penance in the middle of the extreme worldliness of contemporary Christmas celebrations.