I would go with something sleek and stylish. When I think “Cosmopolitan”, I think cocktail attire (which means no jeans). A little black dress is always a safe route to go. You can’t go wrong with a nice dress, or skirt paired with a nice blazer (a tuxedo blazer is a great option), and then finalize everything with some statement jewelry and a nice clutch. Hope this help you out and have fun!