Broken Dark Mode Color Styling

[Araz0]

On all pages; but for this, I will refer to this as an example:
https://backend-development.github.io/rails_associations_and_validations.html

the Code Snippets are taking highlighting colors from the dark mode stylesheet from the code.css file which is seeing that my browser is in dark mode, but the rest of the page (body background and normal text colors) are still on the light mode color styling.

it is hard to read the code snippet in this state.

Browser: Firefox 96.0.2 (64-bit)
Windows 11

issue appears to be happening for multiple users on different browsers as well.