const int ledPin = 11;
const int buttonUpPin = 3;
const int buttonDownPin = 2;

int brightness = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonUpPin, INPUT);
  pinMode(buttonDownPin, INPUT);
}

void loop() {
  if (digitalRead(buttonUpPin) == HIGH) {
    brightness += 10;
    if (brightness > 255) {
      brightness = 255;
    }
    analogWrite(ledPin, brightness);
    delay(100);
  }

  if (digitalRead(buttonDownPin) == HIGH) {
    brightness -= 10;
    if (brightness < 0) {
      brightness = 0;
    }
    analogWrite(ledPin, brightness);
    delay(100);
  }
}