#define LED_PIN D2
#define BUTTON_PIN D8

int brightness = 0;
int stepSize = 64;

bool lastButtonState = HIGH;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
}

void loop() {

  bool currentButtonState = digitalRead(BUTTON_PIN);

  if (lastButtonState == HIGH && currentButtonState == LOW) {

    brightness += stepSize;

    if (brightness > 255) {
      brightness = 0;
    }

    analogWrite(LED_PIN, brightness);

    delay(50); // debounce
  }

  lastButtonState = currentButtonState;
}