The button is directly on the redstone lamp and turns it on or off permanently.
The shifter is a lever replacement, so does exactly what the lever would do in place. But a button is less noticeable.
The structure of the circuit is well visible from the picture, a flipflop and a comparator. The comparator is switched on, so compare.
The special thing about the circuit is that the button is on the lamp, and not somewhere on the wall.
Rear view of the circuit
Example where I have installed the circuit so, I found the lever in the place just too ugly. (Lamp above the bed)