velero/site/layouts/docs/versions.html

<div class="row">
    <div class="dropdown mb-2">
        {{ if $.Site.Params.versioning }}
            <button class="btn btn-primary dropdown-toggle" type="button" id="dropdownMenuButton" data-toggle="dropdown"
                    aria-haspopup="true" aria-expanded="false">
                {{ .CurrentSection.Params.version }}
            </button>
            <div class="dropdown-menu" aria-labelledby="dropdownMenuButton">
                {{ $original_version := printf "/%s/" .CurrentSection.Params.version }}
                {{ $latest_url := replace .Params.url .CurrentSection.Params.version .Site.Params.latest | relURL }}
                {{ $currentUrl := .Permalink }}

                {{ range .Site.Params.versions }}
                    {{ $new_version := printf "/%s/" . }}
                    <a class="dropdown-item"
                       href="{{ replace $currentUrl $original_version $new_version | relURL }}">{{ . }}</a>
                {{ end }}
            </div>
        {{ else }}
            <span>{{ .Site.Params.latest }}</span>
        {{ end }}
    </div>
</div>