hugo-theme-hilfe/layouts/shortcodes/button.html

{{ $ref := "" }}
{{ $target := "" }}

{{ with .Get "href" }}
  {{ $ref = . }}
  {{ $target = "_blank" }}
{{ end }}

{{ with .Get "relref" }}
  {{ $ref = relref $ . }}
{{ end }}

<span class="gdoc-button{{ with .Get "class" }} {{ . }}{{ end }}">
<a {{ with $ref }} href="{{.}}" {{ end }} {{ with $target }} target="{{.}}" {{ end }} class="gdoc-button__link">
  {{ $.Inner }}
</a>
</span>