Fritzing

push buttons must be held down to turn them on or off.

To build this I would use the following arduino code to play with it.

int led = 13; // the pin that the LED1 is attached to
int led2 = 9; // the pin that the LED2 is attached to
int brightness = 0; // how bright the LED is
int fadeAmount = 5; // how many points to fade the LED by

// the setup routine runs once when you press reset:
void setup() { 
// declare pin 9 to be an output:
pinMode(led, OUTPUT);
pinMode(led2, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() { 
// set the brightness of pin 9:
analogWrite(led, brightness);
analogWrite(led2, brightness*-1);

// change the brightness for next time through the loop:
brightness = brightness + fadeAmount;

// reverse the direction of the fading at the ends of the fade: 
if (brightness == 0 || brightness == 255) {
fadeAmount = -fadeAmount ; 
} 
// wait for 10 milliseconds to see the      dimming effect 
delay(10); 
}