In what could be the most powerful fast-fashion alliance yet, Chinese e-commerce juggernaut Shein has struck a deal with Forever 21. The agreement will allow the popular online fashion retailer to sell Forever 21 clothing, accessories and beauty products on its site. In return, Shein could soon operate distinct retail spaces within Forever 21 stores. While Shein has experimented with pop-up stores, including one in Montreal last month, it has no brick-and-mortar stores in North America. The move came as a surprise to some, given the two companies were seen as one of each other's biggest rivals. "In terms of...