Some fonts are still missing from the Appearance menu. I’ve read that this was fixed but at least on my system, it’s not. As far as I can tell, it’s seeing all the English fonts in /System/Library/Fonts but none in /Library/Fonts (where my custom fonts are installed).
This behavior is apparently a security feature of the operating system and/or the underlining web platform. I learned this when I attempted to use Inconsolata as my Obsidian font. In investigating/googling the problem I found that I could not use the font in Safari either and that was the gist of the explanation.
The workaround I applied was to base64 encode the font and then embed it in my custom CSS file as an @font-face. I used Font-Face and Base64 Data-URI as a guide for doing this. Unfortunately, this not for the technically faint of heart.