<div class=“card widget-themes”>

<div class="card-header">
  <strong>Themes switcher</strong>
</div>
<div class="list-group list-group-flush">
  {%- for t in page.themes -%}
  {%- assign t_slug = t | slugify | replace: '-', '_' -%}
  <a href="#" class="list-group-item list-group-item-action{% if t_slug == theme %} active{% endif %}" data-theme="{{ t_slug }}">{{ t }}</a>
  {%- endfor -%}
</div>

</div>