CSS is not working on my GitHub “website”

Hello guys i’ve tried several method to put the website i have created online with GitHub, I finally succed to put CSS and JS files with my index.html but it only display my HTML, my “index.html” file, without any CSS. It’s strange since I’ve put my CSS files on GitHub?

here is my repository : https://github.com/Ziratsu/Ziratsu.github.io

Thank’s if you take time to give me a hand, this is my first real project for a customer, and even if it’s not totally finished I want to give him a look.
(Btw sorry for the eventual english mistakes♥)

Rename the folders to lower case. CSS != css, so the files don’t get found.