Project: lowdb
Task (challenging): 1) Add the .pay-my-order button to /order/:order-id
2) Button is visible when the status is 'Pending payment'
3) When .pay-my-order is clicked:
   - the status of the order becomes 'Finished'
   - the Coin is paid by current user
   - Decrease product quantity
4) If payment fails, update the order status to 'Failed'
5) Create CSS files to beautify CSS
6) DO NOT use a third-party UI library