I like that style on slim woman. A few years ago when crop tops were not a thing (at least no in my country) I was on a vacation in Paris and many women wore it like that, they where all very slim and looked so elegant and well dressed. I mean, even if you have a flat belly I think you shouldn't show it at work/university/school but you can get away with showing 1 or 2 inches of it and still look classy (but casual).