If you need to customize Forgejo, the documentation wasn't clear to me so here is how I customized the font:
$AppWorkPath/custom or /var/lib/forgejo/custom/ if using the binary)./public/assets/css/custom.css :root { --font-proportional: "Custom Font" !important; }./templates/custom/header.tmpl<link rel="stylesheet" href="/assets/css/custom.css">