Custom CSS not loading on preview and not in pdf

[Ugusu]

Everything works perfectly while on local. And when I first deployed it on github pages it worked as well at first. But recently it stopped loading the CSS and the images on github pages. On local still works.

You can check it in my repo: https://github.com/Ugusu/GPA_calculator
And on the github pages page: https://ugusu.github.io/GPA_calculator/

First click the Calculate button, then the Export one. Fields can be empty.

EDIT: It works, when I deploy it on other hosting services, like Netlify: https://asoiutranscript.netlify.app/