{% macro render_toc(toc_items) %}
<ul>
  {% for item in toc_items %}
  <li class="toc-level-{{ item.level }}">
    <a href="{{ item.url }}">{{ item.title }}</a>
    {% if item.children %}
      {{ render_toc(item.children) }}
    {% endif %}
  </li>
  {% endfor %}
</ul>
{% endmacro %}