This is the 3655th most frequent Russian word.
счастья
Happiness.
The word 'счастья' is used here in the genitive case as part of the wish phrase 'желаю счастья', indicating something desired.
Я желаю тебе счастья.
I wish you happiness.
The word 'счастья' is used here to denote 'happiness' in the abstract sense as the object of a prepositional phrase.
Для полного счастья мне не хватает только моря.
For complete happiness, I just need the sea.
Here, 'счастья' follows 'от', showing the cause of the beaming, utilizing the genitive case to express a relation of origin or reason.