hacks-guide-minimal-mistakes-theme/_includes/nav_list

{% include base_path %}
{% assign navigation = site.data.navigation[page.sidebar.nav] %}

<nav class="nav__list">
  <ul>
    {% for nav in navigation %}
      <li><span class="nav__sub-title">{{ nav.title }}</span>
        {% if nav.children != null %}
        <ul>
          {% for child in nav.children %}
          {% assign nav_url = child.path | prepend: "/" | prepend: page.sidebar.nav | prepend: "/" | append: "/" %}
            {% if nav_url == page.url %}
              {% assign active = "active" %}
            {% else %}
              {% assign active = "" %}
            {% endif %}
            <li><a href="{{ nav_url | prepend: base_path }}" class="{{ active }}">{{ child.title }}</a></li>
          {% endfor %}
        </ul>
        {% endif %}
      </li>
    {% endfor %}
  </ul>
</nav>