Radio/CD/AUX etc lights just stopped working

Hey guys, had this car for many years - just went for an errand and noticed that the (already quite dim) lights that backlight the radio buttons (fm, am, cd, aux, etc) are out. the bright green and orange lights for the cd changer are working fine, dash lights work fine, light behind the shifter works fine, lights in the steering wheel work fine! etc. just the little buttons that let you select the audio input have gone dark.

is this replaceable/fixable? or symptom of something worse? It's something I don't mind living with if it's just a weird quirk of an old car.

thanks!