int ledr = 8;         
int ledg = 7;      
int ledb = 6;         
int brightness = 0;  
int fadeAmount = 5;  

void setup() {

  pinMode(ledg, OUTPUT);
  pinMode(ledr, OUTPUT);
  pinMode(ledb, OUTPUT);
}

void loop() {

  analogWrite(ledg, brightness);
  analogWrite(ledr, brightness);
  analogWrite(ledb, brightness);

  brightness = brightness + fadeAmount;

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