mattrbld/_includes/header.njk

<header>
	<nav>
	  <ul>
  	  {% for entry in collections.all | eleventyNavigation %}
        {% if not entry.children.length %}
          <li>
            <a href="{{ entry.url }}" {% if page.url == entry.url %}aria-current="page"{% endif %}>
              {{ entry.title }}
            </a>
          </li>
        {% else %}
          <li class="dropdown">
            <label for="dropdown-{{ entry.title | slugify }}">
              {{ entry.title }}
              <input type="checkbox" id="dropdown-{{ entry.title | slugify }}">
            </label>
            <ul>
       			  {% for child in entry.children %}
                <li>
                  <a href="{{ child.url }}" {% if page.url == entry.url %}aria-current="page"{% endif %}>
                    {{ child.title }}
                  </a>
                </li>
          		{% endfor %}
            </ul>
          </li>
  			{% endif %}
  		{% endfor %}
		<ul>
	</nav>
</header>