Does the fact that "buena" comes before the noun affect its meaning in this case?
Generally, it means that it is an opinion. Or that it is an inherent (always true) property of the object.
Actually I just found this out, so here is my limited knowledge of this fact. When "Buena" comes before the noun it modifies, then you place special emphasis on that noun. For example, "Es una buen biblioteca" Would be "It is a VERY good library," while "Es una biblioteca buena" is "It is a good library."
The adjective behind the noun is also true in other cases, which I will not explain here, but can be found in the following link.
If any of this is incorrect, feel free to set my thinking straight.
"Nice" is more of an emotional remark as opposed to "good" which refers to quality. You wouldn't speak about a library as being nice (kind), mean, etc. That doesn't make sense -- so in Spanish, the same kind of thing. While "buena" can mean "nice", it has to work correctly in the sentence -- i.e. about a person rather than an inanimate object.
Earlier it said bibloteca meant bookcase, so how is it is a good bookcase wrong. I am tring to do the whole lesson without looking at the hints.
Why do they teach us the other possible words if they then won't accept it. I translated 'The bookcase' into La biblioteca but then lose a heart to 'It's a good bookcase'. Tehy wanted bookshelves I suppose but that is a different thing. :(
I'm not sure if you're saying that DuoLingo said that, but that's incorrect. A bookcase= un librero, a shelf= un estante, a bookshelf would be un estante con libros, una biblioteca= a library, una libreria= a bookstore. Hope that helps.
I listened several times. It says "es la buena", not "una buena>' the pronunication is very bad