Translation:Her hair is both black and nice.
URGH. Seriously, who is contributing to this course? “好看" can mean 'pretty', 'beautiful' and 'good-looking' -- and you guys went with 'nice'? This course needs to have contributors who are well-versed in BOTH Mandarin -and- English!
and of course when I translate it as "looks nice" it is marked wrong what the heck
"looks nice" is so much better. I can't think of any circumstance where "好看" would be translated as just "nice".
This should also accept "her hair is both black and nice" although in English we do not tend to say that, we also don't tend to comment on the color and the niceness of someone's hair in the same sentence
This English sentence is just so awkward that I can't really imagine ever saying anything like this, neither these words nor this structure. The closest thing I could think of that would actually be idiomatic is 'She has beautiful black hair' but that as the English example would not help anyone to guess 又黑又好看。But that should certainly be accepted as an English translation.
I translated 好看 as "beautiful" (which it does mean) but was marked incorrect because you chose "nice" as the translation. I echo AmandaLee's comment.
In English we would put "nice and black" so my answer should have been accepted
We would, except that means something different from what the Chinese is saying.