int led1 = 9; 
int led2 = 10; 
int led3 = 11; 

int brightness = 0; 
int fadeAmount = 5; 

void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
}

void loop() {
 
  analogWrite(led1, brightness);
  analogWrite(led2, brightness);
  analogWrite(led3, brightness);
  brightness = brightness + fadeAmount;

  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount;
  }
  
  delay(50);
}