mkdocs-material/src/views/toc.html

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

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

<!-- Render 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>
        {% for toc_item in toc %}
          <li class="anchor">
            <a class="{% if loop.first %}current{% endif %}"
              title="{{ toc_item.title }}" href="{{ toc_item.url }}">
              {{ toc_item.title }}
            </a>
          </li>
        {% endfor %}
      </ul>
    {% endif %}
  </li>
{% endif %}