bulma/docs/_includes/subnav-grid.html

<nav class="navbar has-shadow">
  <div class="container">
    <div class="navbar-tabs">
      <a class="navbar-item is-tab {% if page.doc-subtab == 'columns' %}is-active{% endif %}" href="{{ site.url }}/documentation/grid/columns/">
        Columns
      </a>
      <a class="navbar-item is-tab {% if page.doc-subtab == 'tiles' %}is-active{% endif %}" href="{{ site.url }}/documentation/grid/tiles/">
        Tiles
      </a>
  </div>
</nav>