mkdocs-material/src/nav.html

<!-- Render sections -->
{% if nav_item.children %}
  <li>
    <hr />
    <span class="section">{{ nav_item.title }}</span>
    <ul>

      <!-- Render pages of section -->
      {% for nav_item in nav_item.children %}
        {% include 'nav.html' %}
      {% endfor %}
    </ul>
  </li>

<!-- Render page link -->
{% else %}
  <li>
    <a class="{% if nav_item.active %}current{% endif %}"
      title="{{ nav_item.title }}" href="{{ nav_item.url }}" >
      {{ nav_item.title }}
    </a>

    <!-- Expand active pages -->
    {% if nav_item == current_page %}
      <ul>

        <!-- Render anchors of active page -->
        {% for toc_item in toc %}

          <!--
            The top-level anchor must be skipped if the article contains a h1
            headline, since it would be redundant to the link to the current
            page that is located just above the anchor. Therefore we directly
            continue with the children of the anchor.
          -->
          {% if h1 %}
            {% for toc_item in toc_item.children %}

              <!-- Render anchor -->
              <li class="anchor">
                <a title="{{ toc_item.title }}" href="{{ toc_item.url }}">
                  {{ toc_item.title }}
                </a>
              </li>
            {% endfor %}
          {% else %}

          <!-- Render anchor -->
          <li class="anchor">
            <a title="{{ toc_item.title }}" href="{{ toc_item.url }}">
              {{ toc_item.title }}
            </a>
          </li>
          {% endif %}
        {% endfor %}
      </ul>
    {% endif %}
  </li>
{% endif %}