Mailspring/_includes/sidebar_section.html

<div class="heading">{{include.section.name}}</div>
<ul>
  {% for item in include.section.items %}
    {% if item.items %}
      {% include sidebar_section.html section=item %}
    {% else %}
      <li class="{% if page.url contains item.link %}active{% endif %}"><a href="{{item.link}}" {% if item.external %}target="_blank"{% endif %}>{{item.name}}</a></li>
    {% endif %}
  {% endfor %}
</ul>