2001 - S500

I'm trying to figure out if the temperature control (buttons that have blue and red arrows on them) both the right and left light up. Last night when I took a look at the buttons only the left button was lit. The right button along with air volume button (the button between the temperature button that has a picture of a fan and two arrows) were not lit. Can some please tell me how this works. If there is a problem, are these bulbs that I can change.