bulma/docs/_includes/docs/menu-item.html

{% assign link = site.data.links.by_id[include.link_id] %}
{% assign has_sublist = include.sublist_id != nil %}
{% assign sublist_size = site.data.links.categories[include.sublist_id] | size %}
{% assign current_category = page['doc-tab'] %}
{% assign is_current = current_category == include.sublist_id %}

<li>
  {%
    include docs/menu-link.html
    link=link
    link_id=include.link_id
    has_sublist=has_sublist
    sublist_size=sublist_size
    is_current=is_current
  %}

  {% if has_sublist %}
    <ul
      class="bd-menu-sublist {% if current_category == include.sublist_id %}is-open{% endif %}"
      style="--subsize: {{ sublist_size }}"
    >
      {% for sublink_id in site.data.links.categories[include.sublist_id] %}
        {% assign sublink = site.data.links.by_id[sublink_id] %}
        <li>
          {% include docs/menu-link.html link=sublink link_id=sublink_id %}
        </li>
      {% endfor %}
    </ul>
  {% endif %}
</li>