sass-site/source/_includes/documentation_toc.liquid

<ul>
  {%- if parent_href -%}
    <li class="overview">
      <a href="{{ parent_href }}" {% if url == parent_href %}class="selected"{% endif %}>Overview</a>
    </li>
  {%- endif -%}
  {%- for section in toc -%}
    {%- assign link = section | getDocTocData -%}
    {%- assign children = section[':children'] -%}
    {%- assign is_open = url == '' and link.expanded -%}
    <li>
      <a href="{{ link.href }}" class="{% if children %}section {% endif %}{% if url | startsWith: link.href %}open selected{% elsif is_open %}open{% endif %}">{{ link.text }}</a>
      {%- if children -%}
        {% render 'documentation_toc', url: url, toc: children, parent_href: link.href %}
      {%- endif -%}
    </li>
  {%- endfor -%}
</ul>