const int ledPin1=25;
const int ledPin2=26;
void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:
  for (int i=0; i<=255; i++) {
  dacWrite(ledPin1, i);
  dacWrite(ledPin2, 255-i);
  delay(2);
  }
 for (int i=255 ; i>=0; i--) {
  dacWrite(ledPin1, i);
  dacWrite(ledPin2, 255-i);
  delay(2);
  }
}