For a relaxed outfit, consider teaming a black crew-neck t-shirt with khaki cargo pants — these two pieces play pretty good together. If you need to immediately dial down this outfit with one item, complement your outfit with green-yellow athletic shoes. A cool ensemble that transitions easily into fall like this one makes it extremely easy to embrace the new season. Those wondering how to wear modern casual outfits as you move through your 20s, you have your answer.