"You are nice!"
What Troll1995 said, except καλή is the feminine form, whereas the other two are masculine.
Ωραίος, καλός, όμορφος.
Ωραία, καλή, όμορφη.
Ωραίο, καλό, όμορφο.
I'd seen 'ωραίος' translated as 'beautiful' before. Can it be used as a compliment on physical appearance too?
Because ωραίο is the neuter form of the adjective.. I don't think you'd refer to someone using neuter singular, unless that was some sort of animal/pet. :P
Sometimes "nice" encompasses that meaning too, but the same happens in Greek. Somebody may be "καλός" (which is an accepted translation here) because they are "ευγενικός"=polite. So I think it's best to keep them separate.