Can fina and trevliga be fine?
No, it sounds quite non-idiomatic to refer to clothes as trevliga.
Would "He has nice clothes" be "Han har fina kläder"?
What about vackra kläder?
I tried vackra kläder and it was wrong!?
I used "snälla" and it wasn't accepted. "Nice" is a very vague word. What are the ranges of use for fin, snäll, trevlig, vackar, etc.?