Theme Switching

Hi guys, im hosting my website on Github Pages (bsod2528.github.io)

I want to have a feature where people can switch themes (light and dark). I’ve tried via scss variables, its a freaking pain because i cant change properties like background if the scss file is not in the main.scss

please do check my source code at: GitHub - bsod2528/bsod2528.github.io: its a website

Please do give ideas on how i can do this thank you.