Go for a white crew-neck t-shirt and a dark green polo if you seek to look laid-back and cool without exerting much effort. Grey athletic shoes are the most effective way to infuse an element of stylish casualness into this ensemble. When it comes to dressing for unpredictable fall weather, nothing beats a knockout combo that can take you from season to season. Those who are curious how to sport modern off-duty style in your 20s, you have your answer.