If we are speaking about greetings etc., where the case is accusative (or 4th case) –because it is shortened "Přeji Vám dobré odpoledne" = "I wish you good afternoon"– then:
feminine: Dobrou noc = Good night
plural feminine (and masculine):
Veselé Vánoce = Merry Christmas
Veselé Velikonoce = Happy Easter
In plural neuter accusative, hard adjectives should end with á, but I dare say that standard ("correct") neuter endings are not very popular with Czechs.
I can only recommend you to have a look at declension overview (hope it won't scare you a lot): http://mluvtecesky.net/en/grammar/adjectives https://en.wikipedia.org/wiki/Czech_declension#Adjective