where is css source saved?

Not sure if my topic title is clear, but I’m trying to link uploaded fonts within my css.

Using a traditional css file within a theme directory and my fonts saved in a folder called “fonts”, I’d direct the css to

src: url('fonts/nameoffont.eot

But that doesn’t seem to work now. Advice appreciated.

https://ww.wp.xz.cn/plugins/simple-custom-css/