[Requesting Assistance] Importing Font via custom.css

[syphant]

Total noob here.
This isn't a bug per se but I'm not sure why I can't seem to get a custom font working in Homer.

My config.yml contains the below:

stylesheet:
   - "assets/custom.css"

And my custom.css consists entirely of the following:

@font-face {
  font-family: "JetBrains Mono";
  src: url("./fonts/JetBrainsMono-Regular.woff2") format("woff2");
  src: url("./fonts/JetBrainsMono-Regular.ttf") format("truetype");
}

body h1, body h2, body h3, body h4, body h5, body h6 {
  font-family: "JetBrains Mono";
}

But no dice.
Can anyone steer me in the right direction?