website/layouts/shortcodes/details.html

{{- $summary := "" -}}
{{- if .IsNamedParams -}}
  {{- $summary = .Get "summary" -}}
{{- end -}}
<details>
  {{- if ne $summary "" -}}
    <summary>{{ $summary }}</summary>
  {{- end -}}
  <div class="details-inner">
    {{ .Inner | markdownify }}
  </div>
</details>