Back in the 70's, the person that wired the cabin (not a pro) mounted a ceiling light with the junction box located below the ceiling (not flush with the ceiling) and a ceramic light bulb fixture attached to the bottom. How do I install a decent light fixture with this set-up?
you may be able to cut in a pancake box to make it flush.If that is not an option you could cut a block of wood to cover the box and paint it to match the ceiling. If the box doesn't bother you it should fit on the box you have.
They make round remodel box that after you cut out the round hole in your ceiling it has ears that pinch the box between the ceiling or you can get a foam "medallion" that would go around your box and the same thickness as the box and gives it a finished look.