You probably want to do something like what is on the model on the website. Since the pants are pretty simple in terms of pattern/embellishment, you can either go simple like the top in the picture or you can wear something more patterned. I think that a flowy, loose-fitting shirt will compliment the pants nicely since wearing a tight shirt will make your hips look bigger than they are. Try and go with neutral colors (black, white, gray, tan) or earthy colors (brown, green, off-white, darker reds and yellows)
