Designer Michael Kors poses backstage before the Michael Kors Collection Fall 2017 runway show at Spring Studios on February 15, 2017 in New York City.NEW YORK CITY — In a federal courtroom on Monday, storied fashion designer Michael Kors spoke about the steep challenge of staying relevant in a world where brands can rise and fall based on viral TikTok videos and photos of handbags on the arms of celebrities like Taylor Swift and Beyoncé.Kors kicked off the week of testimony in the antitrust trial in Manhat ...