And endless, in a Swedish winter.
-och ful av skräck.
"Ful" means ugly, I think you meant "full". :D
Why svarta? Why not svart
It's the plural form of the adjective.
Is the rule simply svart for singular and svarta for plural, or is there something more regarding en and ett words?
och så är dagarna
It says i have a typo, but it was correct
There's some kind of problem with typo handling at the moment, but since no one can see what you put, I can't tell you if that was what happened in your case.
...och full av skräck!