grammer correct?

Some hills are in the background of the painting.

Background/foreground is more than a way of describing depth perception in realistic pictures.

Do you like the work of art ? Why ?

Every work of art is unique, which is not reproducible. Arts of work have aesthetic appeal. Unlike movies, great art, however, is not the product of conscious economic motives, though it may be the by-product, but it is inspired and impelled by an aesthetic experience.
That is why I generally like work of art.

Comment:
"Behind" can be a noun ~ different meaning

Behind (noun) = the part of the body on which a person sits.
He tripped and fell on his behind.

Wrong!

"At" is a preposition
A preposition should always be followed by a noun, pronoun, noun phrase or noun clause.
"Behind" is a preposition.

It should be
There are some hills in the background of the painting.