site/_includes/primary-nav-items.html

<ul>
  <li class="{% if page.overview %}current{% endif %}">
    <a href="/">Home</a>
  </li>
  <li class="{% if page.url contains '/docs/' %}current{% endif %}">
    <a href="/docs/"><span class="show-on-mobiles">Docs</span>
                     <span class="hide-on-mobiles">Documentation</span></a>
  </li>
  <li class="{% if page.url contains '/talks/' %}current{% endif %}">
    <a href="/talks/">Talks</a>
  </li>
  <li class="{% if page.url contains '/news/' %}current{% endif %}">
    <a href="/news/">News</a>
  </li>
  <li class="{% if page.url contains '/help/' %}current{% endif %}">
    <a href="/help/">Help</a>
  </li>
  <li class="{% if page.url contains '/develop/' %}current{% endif %}">
    <a href="/develop/">Develop</a>
  </li>
</ul>