Dress in a black vertical striped long sleeve shirt and charcoal skinny jeans to be both modern casual and practical. To bring a little flair to this outfit, introduce a pair of black leather chelsea boots to the mix. As you can see here, it's super easy to look seriously stylish and stay comfortable when chillier weather comes, all thanks to outfits like this one. Those who wonder how to sport modern casual dressing as you navigate your 20s, you have your answer.