Much has already been written about the emergence of "fast fashion": clothing retailers that are able to translate trends seen on the world's fashion runways... to a store near you in a matter of weeks. The success stories of Sweden's H&M and Spain's Mango have become the stuff of business legend in upending the fashion industry in recent decades. It was probably only a matter of time that onetime suppliers in China would become the firms at the cutting edge of evolving to customer's whims and desires that move so quickly. Younger women should be familiar with China-based online retailer Shein. Reflecting the democratization...