const int ledPin = 9; // PWM-capable pin to which the LED is connected

void setup() {
  pinMode(ledPin, OUTPUT); // Set the LED pin as an output
}

void loop() {
  // Fade in the LED
  for (int brightness = 0; brightness <= 255; brightness++) {
    analogWrite(ledPin, brightness); // Set the brightness
    delay(10); // Wait for 10 milliseconds to see the change
  }

  // Fade out the LED
  for (int brightness = 255; brightness >= 0; brightness--) {
    analogWrite(ledPin, brightness); // Set the brightness
    delay(10); // Wait for 10 milliseconds to see the change
  }
}