maxtar.github.io/themes/hugo-geekdoc/layouts/shortcodes/mermaid.html

<!-- prettier-ignore-start -->
{{ if not (.Page.Scratch.Get "mermaid") }}
  <!-- Include mermaid only first time -->
  <script defer src="{{ index (index .Site.Data.assets "mermaid.js") "src" | relURL }}"></script>
  {{ .Page.Scratch.Set "mermaid" true }}
{{ end }}
<!-- prettier-ignore-end -->

<pre class="gdoc-mermaid mermaid{{ with .Get "class" }}{{ printf " %s" . }}{{ end }}">
  {{- .Inner -}}
</pre>