So, dress (il vestito) cannot be feminine? Because I translated this as "La vestita e (as in it is, not and) bella," and it said that was incorrect. Instead it insists on "Il vestito e bello." So vestito must be masculine??
Perhaps be-cause women are usually the ones to wear dresses, Italian would make it masculine to complement? Alternatively, in Ancient Rome, "civilised" men wore skirts, and "barbarians" wore pants, so perhaps it's related to that
Why not "il abito è bello." ? It was marked wrong by Duolingo. Nevertheless if I google "il abito bello" I get lots of wedding dresses with texts like "Abito da sposa più bello del mondo". So I think it should be correct.