bulma/docs/_includes/subnav-modifiers.html

<nav class="nav has-shadow">
  <div class="container">
    <div class="nav-left">
      <a class="nav-item is-tab {% if page.doc-subtab == 'syntax' %}is-active{% endif %}" href="{{ site.url }}/documentation/modifiers/syntax/">
        Syntax
      </a>
      <a class="nav-item is-tab {% if page.doc-subtab == 'helpers' %}is-active{% endif %}" href="{{ site.url }}/documentation/modifiers/helpers/">
        Helpers
      </a>
      <a class="nav-item is-tab {% if page.doc-subtab == 'responsive-helpers' %}is-active{% endif %}" href="{{ site.url }}/documentation/modifiers/responsive-helpers/">
        Responsive helpers
      </a>
    </div>
  </div>
</nav>