beautifulSA-jekyll/_includes/nav.html

<nav class="navbar navbar-expand-md navbar-light fixed-top navbar-custom {% if page.nav-short %}top-nav-short-permanent{% endif %}">

  {%- if site.title-img -%}
    <a class="navbar-brand navbar-brand-logo" href="{{ '' | absolute_url }}"><img alt="{{ site.title }} Logo" src="{{ site.title-img }}"/></a>
  {%- elsif site.title -%}
    <a class="navbar-brand" href="{{ '' | absolute_url }}">{{ site.title }}</a>
  {%- endif -%}

  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#main-navbar" aria-controls="main-navbar" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="main-navbar">
    <ul class="navbar-nav ml-auto">
      {%- for link in site.navbar-links -%}
        {%- if link[1].first %}
          <li class="nav-item dropdown">
            <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">{{ link[0] }}</a>
            <div class="dropdown-menu" aria-labelledby="navbarDropdown">
              {%- for childlink in link[1] -%}
                {%- for linkparts in childlink %}
                  <a class="dropdown-item" href="{{ linkparts[1] | relative_url }}">{{ linkparts[0] }}</a>
                {%- endfor -%}
              {%- endfor %}
            </div>
          </li>
        {% else %}
          <li class="nav-item">
            <a class="nav-link" href="{{ link[1] | relative_url }}">{{ link[0] }}</a>
          </li>
        {%- endif -%}
      {%- endfor -%}
    </ul>
  </div>

  {% if site.avatar and (layout.show-avatar or page.show-avatar) %}
    <div class="avatar-container">
      <div class="avatar-img-border">
        <a href="{{ '' | absolute_url }}">
          <img alt="Navbar avatar" class="avatar-img" src="{{ site.avatar | relative_url }}" />
        </a>
      </div>
    </div>
  {% endif %}

</nav>