Shares of Overstock.com Inc. rallied more than 20% in the extended session Thursday after news about a private-equity investment overshadowed a larger-than-expected quarterly loss for the online retailer. Hong Kong private-equity firm GSR Capital has agreed to invest in the company and its blockchain unit, tZero, Overstock said. GSR Capital plans to invest up to $374.55 million in exchange for tZero shares and Overstock.com shares, according to a statement. Overstock and GSR Capital also agreed that GSR Capital will buy $30 million in tZero security tokens from Overstock.