Dark isn't even a thing. It's a descriptor of a lack of light.

Put another way "dark" is just a way of describing light.

Light exists as an actual thing, it's absence is what we call darkness.

Much in the same way that "cold" describes an absence of heat.

Th opposite of light is not dark. When you sum two opposites you get zero. When you sum "darkness" and light, you still get light.

As far as I know, there is no Anti-light.