{%- assign catcounter = page.categories | size -%}
{%- if catcounter >= 1 -%}
<div id="accordion">
  <div class="card">
    <div class="card-header sidebar-card" id="catwidget">
      <h3 class="mb-0">
        <button class="btn btn-link collapsed" data-toggle="collapse" style="font-size:1.25em" data-target="#catcontents" aria-expanded="false" aria-controls="collapseOne">
          Categories
        </button>
      </h3>
    </div>
    <div id="catcontents" class="collapse" aria-labelledby="catwidget" data-parent="#accordion">
      <div class="card-body" style="padding:0">
        <ul class="list-group list-group-flush">
          {%- for category in page.categories -%}
          <li class="list-group-item"><a href="/categories.html#{{ category | slugify }}">{{ category }}</a></li>
          {%- endfor -%}
        </ul>
      </div>
    </div>
  </div>
</div>
{%- endif -%}