okay I have now found out what Stylish is.
It is a third party browser extension you have used client-side to over-ride the styles of the forum test page.
That explains how you styled my web page and took a screenshot (clever).
The wikipedia article on Stylish states
Stylish is often compared to Greasemonkey, another Mozilla extension that allows client-side manipulation of web pages.
I myself have always tried to avoid using Greasemonkey or similar 3rd party browser plugins.
Anyway you only used it to tinker with the styles at your end to get a nice appearance.
I don't have a problem with any suggested style changes and I also always write valid CSS, that is not a problem.
I validate my CSS using the W3C checker, which I trust to be correct and I have used it for many years.
I don't really want to complicate things by looking through 3rd party plugin additions to the CSS as that could become a nightmare. Be cautious about trusting 3rd party error messages, that might be due to interactions caused by the plugin.
So to keep it simple I would rather you show me a screenshot, like you did before (Stylish or no Stylish, I don't mind) and I will hand code the CSS to look the same.
You located the font code easily enough and now from that we know what to apply globally, if you want that font across the whole forum. I can do that.
Please check my updated forum test page
http://www.kdworld7.net/smf/index.php (in a browser without Stylish modifying the stlye) and indicate any changes you would like and we can continue as before.
Hope this is ok.
Thanks.