You have to enter either "HOLIDAY20" or "HOLIDAY30" as a promo code at the end of the checkout process. The former will work for either $40 or $60 games, but I believe the latter will only work for $60 games.

A few highlights:

• Super Mario Bros. Wonder (with caddy and case)
• Spider-Man 2 (PS5, with headset - comes out to $60 with the discount)
• Metroid Prime: Remastered

EDIT: I recently learned that the $30 deal, at least, will only last for the next day (give or take a few hours).