t="ahem">
<link rel="stylesheet" href="/fonts/ahem.css" type="text/css">
<style>
body {
  font-family: serif;
}
p {
  font-family: monospace;
  --a: SomeUnknownFont, var(--b);
  --b: Ahem;
  font-family: var(--a);
}
</style>
<p>This text must be in Ahem.</p>
