cupper-hugo-theme/layouts/partials/footer.html

<footer role="contentinfo">
  <div
  {{ if eq .Site.Params.showThemeSwitcher false }}style="display: none;"{{ end }}
  >
    <label for="themer">
      {{ T "dark_theme" }} <input type="checkbox" id="themer" class="vh">
      <!-- Shows "on" or "off" -->
      <span aria-hidden="true"></span>
    </label>
  </div>
  {{ with .Site.Params.footer }}
    {{ . | markdownify }}
  {{ end }}
</footer>