int B = 12, L1 = 0, L2 = 2;

void setup() {
  pinMode(B, INPUT_PULLUP);
  pinMode(L1, OUTPUT);
  pinMode(L2, OUTPUT);
}

void loop() {
  bool pressed = !digitalRead(B);

  digitalWrite(L1, pressed);   // ON when pressed
  digitalWrite(L2, !pressed);  // ON when released
}