From the owners manual:
Dimmer Controls
With the parking lights or headlights on, rotating the right dimmer control upward will increase the brightness of the instrument panel lights. Rotating the left dimmer control will adjust the interior and ambient light levels.
The left one controls "ambient lighting", which doesnt exist in certain trims, but they put the dimmer in anyway...or at least that's my understanding
EDIT...I looked carefully at my Sport. If it's super dark and I turn the lights on, but the dashlights as far down as possible, and turn the left wheel all the way up, there is a tiny glow barely visible by the door handles. Jeez, why even bother? I get more light from the hands of my watch.
Still dont see any lights in the footwells, though
Since you have a Sport, it only controls the very small LEDs in the door handles.
To see the effect, you need a dark night, engine has to be in Run, lights have to be on, and if you watch very closely you'll see the effect. It works, but in the Sport it's nothing to even think about!