There are lots of songs you can practice throughout the piano chords course and here are some Christmas themed songs.
These are great for not only practicing the chords but also melody and embellishments. Because they are so familiar to so many people and you hear them so often, they can be really useful to practice.
Here is a list of Christmas carols you can use throughout the course. I’ve put them in order of the type of chord being learned so you can choose something similar to what you’re practicing now.
Major and Minor Chords
Slash Chords (C/G)
Minor 7th m7
Major Seventh M7
Chestnuts roasting on an open fire
Fm6 = F Ab C D