The nixpkgs bump to nixos-26.05 pulls in Zola 0.22, which replaced the
syntect highlighting backend with Giallo and changed the config schema.
Replace the removed `highlight_code` key with a `[markdown.highlighting]`
table using the `one-dark-pro` theme.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
asmir
