I have been tinkering around in the config files for the Frio theme on my server. I would like to change the font to Source Sans Pro instead of Open Sans. Is there any way to do this? (Feel free to refer me to other materials/answers if this has already been asked and answered.)

I'm running Friendica on Yunohost and the installation directory is slightly different from versions of Friendica compiled from source: it's in /var/www/friendica/ instead of /var/lib/friendica.

I have tried creating a new directory in /var/www/friendica/view/theme/frio/font/ for Source Sans Pro -- the fonts themselves and the CSS file: /source_sans_pro/fonts/ and /source_sans_pro/source-sans-pro.css. I tried editing the entries in there so they referred to Source Sans Pro by name and the font files I uploaded to the /fonts/ folder that I'd just created. When I uploaded them, I created folders for each of the font files (Black, Bold, Semibold, etc.; italics too).

In ./frio/css/style.css I have also tried editing:

body { ... font-family: "Open Sans", sans-serif ... }
...to "Source Sans Pro", but none of this has worked. All I've managed to do is get my browser to refer to the fonts that are on my device rather than to the ones on the server.

Is there something I am missing?

I don't know if it's important, but I notice the original entries in Open Sans's .css file in /var/www/friendica/view/theme/frio/font/ have
a) version numbers on the end of the URLs/paths to source directories; and
b) font file types that don't exist on the server -- Open Sans is only present as .ttf files, but the URLs specify .eot, woff and even .svg files too.
I tried copying (b) for Source Sans Pro but this did not work. I didn't try (a) with it because I didn't know how (or if) the version numbers helped.