Is there a way to make a custom color mode inherit from dark mode?

[LHGORHAM97]

I have a light mode and a dark mode for my application, but I wanted to add a third custom color mode option for users. I wanted the third color mode to be similar to this Hacker theme: https://brobin.github.io/hacker-bootstrap/#

I am having trouble though because it seems that the custom color modes automatically inherit from light mode, so I have to make adjustments to almost every single variable, and I am unable to change things such as the overflow bar or certain svg images (like the carrots on the form select).

Since I am already using the dark mode on my applications and I do not want to edit it to look like the Hacker theme, I was wondering if there was a way to change what theme the custom color mode inherits from?