// the setup function runs once when you press reset or power the board

void setup() {
  pinMode(10, OUTPUT);// initialize digital pin LED_BUILTIN as an output.
  pinMode(11, OUTPUT);
}

void loop() {   // the loop function runs over and over again forever
  
  for (int i = 0; i <= 255; i++) {
    analogWrite(10, i);
    //delay(1); 
      for (int j = 255; j >= 0; j--) {
        analogWrite(11, j);
        //delay(1);
      }        
  }
  for (int i = 0; i <= 255; i++) {
    analogWrite(11, i);
    //delay(1);
      for (int j = 255; j >= 0; j--) {
        analogWrite(10, j);
        //delay(1);
      }        
  }
}