Problem linking css and other html fles to index.html

[SanderSoetaert]

Hello guys

I have a problem uploading my website. I made my website manually and know i have uploaded all my files ( html and css) into the folder httpdocs/. When I go to my website, i can see my index page but there's no css linked on it and when I press a tab button, I am redirected to a 404 error page. It seems like it doesn't find the files but they are in the map. I checked my links and they work when click on the preview button on Plesk. Can someone help me?

 

[SanderSoetaert]

Another thing I find out, when i change the index.html page in the HTML editor and then reload my website, it doesn't change.. Very weird.. Plz someone help me