Fast fashion — the idea that clothing trends change rapidly and so should the stock of retailers — was pioneered by brands like Zara, H&M and Forever 21, and predicated on speedy supply chains and low cost production. Now, a little-known Chinese brand named Shein is disrupting the fashion industry by using slick social media campaigns and aggressive promotions on TikTok, Facebook and Instagram to sell ultra low-cost clothing to teens and college-aged consumers throughout the world. And it’s doing it primarily through online clicks.  Pop icons Katy Perry and Lil Nas X performed at its online digital festival last year, attracting 1.6 million viewers. And of the world’s most highly trafficked websites in the lifestyle, fashion and apparel category, Shein now ranks No. 1, ahead of global brands like Nike, Zara, H&M, Uniqlo and Gap, according to the web analytics firm Similarweb. “What sets Shein apart is its mastery of this generation’s preferred marketi