Errors in W3C CSS file

Hi.

When you put the link for W3C's own CSS into the W3C validator page
https://jigsaw.w3.org/css-validator/validator?uri=http%3A%2F%2Fwww.w3schools.com%2Flib%2Fw3.css&profile=css3&usermedium=all&warning=1&vextwarning=&lang=en

IT PARTIALLY FAILS.

I am using some of the code from the W3C CSS.

For example, I use w3-padding-2 in the header and my page looks fine. This
isn't in the style sheet. The closest is w3-padding-4, which doesn't work
for me.

There are other things I question but can someone tell me what is going on
here?

Thanks,
Jim