just-the-docs/_includes/components/sidebar.html

<div class="side-bar">
  <div class="site-header">
    <a href="{{ '/' | relative_url }}" class="site-title lh-tight">{% include title.html %}</a>
    <a href="#" id="menu-button" class="site-button">
      <svg viewBox="0 0 24 24" class="icon"><use xlink:href="#svg-menu"></use></svg>
    </a>
  </div>
  <nav aria-label="Main" id="site-nav" class="site-nav">
    {% assign pages_top_size = site.html_pages
          | where_exp:"item", "item.title != nil"
          | where_exp:"item", "item.parent == nil"
          | where_exp:"item", "item.nav_exclude != true"
          | size %}
    {% if pages_top_size > 0 %}
      {% include nav.html pages=site.html_pages key=nil %}
    {% endif %}
    {%- if site.nav_external_links -%}
      <ul class="nav-list">
        {%- for node in site.nav_external_links -%}
          <li class="nav-list-item external">
            <a href="{{ node.url | absolute_url }}" class="nav-list-link external">
              {{ node.title }}
              {% unless node.hide_icon %}<svg viewBox="0 0 24 24" aria-labelledby="svg-external-link-title"><use xlink:href="#svg-external-link"></use></svg>{% endunless %}
            </a>
          </li>
        {%- endfor -%}
      </ul>
    {%- endif -%}
    {% if site.just_the_docs.collections %}
      {% assign collections_size = site.just_the_docs.collections | size %}
      {% for collection_entry in site.just_the_docs.collections %}
        {% assign collection_key = collection_entry[0] %}
        {% assign collection_value = collection_entry[1] %}
        {% assign collection = site[collection_key] %}
        {% if collection_value.nav_exclude != true %}
          {% if collections_size > 1 or pages_top_size > 0 %}
            {% if collection_value.nav_fold == true %}
              <ul class="nav-list nav-category-list">
                <li class="nav-list-item{% if page.collection == collection_key %} active{% endif %}">
                  {%- if collection.size > 0 -%}
                  <a href="#" class="nav-list-expander"><svg viewBox="0 0 24 24"><use xlink:href="#svg-arrow-right"></use></svg></a>
                  {%- endif -%}
                  <div class="nav-category">{{ collection_value.name }}</div>
                  {% include nav.html pages=collection key=collection_key %}
                </li>
              </ul>
            {% else %}
              <div class="nav-category">{{ collection_value.name }}</div>
              {% include nav.html pages=collection key=collection_key %}
            {% endif %}
          {% else %}
            {% include nav.html pages=collection key=collection_key %}
          {% endif %}
        {% endif %}
      {% endfor %}
    {% endif %}
  </nav>

  {% capture nav_footer_custom %}
    {%- include nav_footer_custom.html -%}
  {% endcapture %}
  {% if nav_footer_custom != "" %}
    {{ nav_footer_custom }}
  {% else %}
    <footer class="site-footer">
      This site uses <a href="https://github.com/just-the-docs/just-the-docs">Just the Docs</a>, a documentation theme for Jekyll.
    </footer>
  {% endif %}
</div>