CSS file works offline but not when uploaded to webserver

I just completed my portfolio website and uploaded it to a subdomain of my parent website.

Now the website works fine except that my main styling CSS doesn't work, no errors in the console, nothing. It just doesn't work. I verified it by placing the CSS in <style> tags in the head of my index.html and it worked but then it messed up with my paroller.js plugin, no errors in the console but paroller.js stopped working.

If I include the CSS like I've included it offline (in a separate file, like I always do and it always works on the same web server) it just doens't work. If I include it in the index.html my paroller.js plugin stops working.

Everything works fine offline.

I'm importing the CSS like this - <link rel="stylesheet" href="folername/filename.css">
Please note that I am loading multiple CSSs and this one is the first to be loaded. All other CSSs seem to be working.

The webpage is located at - https://yadullah.piware.tech