Shouldn't the alternative "such an ugly thing" also be accepted? To me, it sounds more natural.
That is accepted. Please always report complete sentences, also using "My answer should be accepted".
You pressed "The correct solution is unnatural" but here you are saying something else. We can't see which "correct solution" you were offered.
why, is it ošklivou věc?
accusative of ošklivá věc
Or which part do you not understand?