A keyboard and a shopping cart are seen in front of a displayed Shein logo in this illustration picture taken October 13, 2020. REUTERS/Dado Ruvic/Illustration NEW YORK, Aug 4 (Reuters) - The meteoric rise of shopping platforms selling Chinese-made goods, including Shein and Temu, has been fueled by a decades-old loophole that allows cheap products like $10 dresses to land in U.S. mailboxes tariff-free. This happens thanks to a "de minimis" rule exempting packages valued at $800 or less from tariffs as long as they're addressed and shipped to individuals. The exemption is open to all retailers but is most...