{{- $index := .Parent.Scratch.Get "tab-index" | default 0 -}}
{{- .Parent.Scratch.Set "tab-index" (add 1 $index) -}}
<div class="tab__panel {{ if eq $index 0 }}tab--active{{ end }}" data-tab-index="{{ $index }}">
  {{ .InnerDeindent | strings.TrimSpace | .Page.RenderString }}
</div>