Praznični Pozdravi

Nearly every Serbian holiday wish starts with the same adjective — and it changes ending to match whatever comes next, exactly like dobar / dobra / dobro:

srećan + masculine — srećan Božić, srećan rođendan, srećan Vaskrs
srećna + feminine — srećna Nova godina, srećna slava
srećni + plural — srećni novogodišnji praznici, srećni praznici

Two of these greetings work as a call and response — one person says the first half, the other answers. At Christmas: Hristos se rodi! → Vaistinu se rodi! At Easter: Hristos vaskrse! → Vaistinu vaskrse! You'll most often see them written in Cyrillic — Христос се роди, Христос васкрсе.

One thing you'll notice out in the wild: people often write Srećnu Novu godinu instead of Srećna Nova godina. Both are correct — the first is the accusative, left over from the full sentence Želim ti srećnu Novu godinu. Here we're practising the plain form.