Fonts are stored on your system, not in the Obsidian app. Depending on your OS you will find instructions online for how to install custom fonts. Once you install the font on your system you will be able to select it as an option in Obsidian.
Hi @KarlMill, @kepano is correct in that Obsidian will need to use an installed font. For the local website you created the browser was allowing the webpage to use a non-installed font. For programs like Obsidian, you will need to use a system installed font.
There was something I saw in a theme file before where they loaded the entire font file into the CSS, but that makes the css file huge. not sure if this method still works or not but I assume it does. I can’t find which theme that was so here is a website explaining how to do it in regular CSS but it should work in Obsidian CSS too. Basically, the bytes of the font file are converted into ascii characters and pasted in the CSS file with some css font commands.