Add two new routes to your playground app. One route will display the landing page, and another will handle the incoming url parameter.
Both routes will load the same HTML template.
Add a new HTML template that will display different UI (buttons, colors, images, etc.) depending if the LED is on or off, and allow the user to turn on or off with a button press.
Use Gpio zero to toggle the led and read its value.
Use conditionals to change led from on to off.
Wire and connect the Pi to an LED.
[optional] add a condition to test if there is a pin at a location before loading the page. Display the error if no LED detected.