---

#define LED1_PIN 3
#define LED2_PIN 5

void setup() {
  pinMode(LED1_PIN, OUTPUT);
  pinMode(LED2_PIN, OUTPUT);
}

void loop() {

  // LED1: 0% → 72%
  // LED2: 72% → 0%
  for (int i = 0; i <= 72; i++) {
    analogWrite(LED1_PIN, map(i, 0, 100, 0, 255));
    analogWrite(LED2_PIN, map(72 - i, 0, 100, 0, 255));
    delay(5000 / 72);
  }

  // LED1: 72% → 0%
  // LED2: 0% → 72%
  for (int i = 72; i >= 0; i--) {
    analogWrite(LED1_PIN, map(i, 0, 100, 0, 255));
    analogWrite(LED2_PIN, map(72 - i, 0, 100, 0, 255));
    delay(5000 / 72);
  }
}