site_opytex/theme/templates/partial/toctree.html

<ul class="toctree">
    {% for cat, articles in categories|sort %}
    {% if (article and article.category == cat) or category == cat %}
    <li class="toctree-l1 current"><a href="{{ SITEURL }}/{{ cat.url }}">{{ cat | upper }}</a>
        <ul>
        {% for art in articles | sort(attribute="date") %}
        {% if article == art %}
        <li class="toctree-l2 current"><span>{{ art.title }}</span></li>
        {% else %}
        <li class="toctree-l2"><a href="{{ SITEURL }}/{{ art.url }}">{{ art.title }}</a></li>
        {% endif %}
        {% endfor %}
        </ul>
    </li>
    {% else %}
    <li class="toctree-l1"><a href="{{ SITEURL }}/{{ cat.url }}">{{ cat | upper }}</a>
    {% endif %}
    {% endfor %}
</ul>