Mailspring/_includes/sidebar_section.html

<div class="section">
  <a class="heading" href="{{include.section.link}}" {% if include.section.external %}target="_blank"{% endif %}>{{include.section.name}}</a>
  <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>
</div>