Darkness is defined as the “absence of light.” Goodness must have good as it’s source. The ancient Hebrews described this as ‘light’. Evil is the absence of good and described as ‘darkness’.
Evil (darkness) is not something. It is the lack of good (light).
The rightness of the moral law reflects the righteous source of the moral law.
“Righteous are you, O Lord, and right are your rules.” (Ps. 119:137)
An intrinsically good source produces goodness. It is reflective of it’s essence. Where there is no good, evil exists. Where there is no light, darkness exists.
“The unfolding of your words gives light;
it imparts understanding to the simple.” (Ps 119:130)