_includes/header.html

{% comment %} capture the current page {% endcomment %}
{% for entry in site.data.navigation %}
    {% capture fullurl %}{{ entry.url | absolute_url }}{% endcapture %}
    {% if fullurl == page.url %}
        {% assign current_page = fullurl %}
        {% break %}
    {% elsif page.url contains fullurl %}
        {% assign current_page = fullurl %}
    {% endif %}
{% endfor %}

<nav class="navbar navbar-expand-lg navbar-light bg-light sticky-top shadow-lg">
    <div class="container d-flex justify-content-between w-100">
            <div class="mr-auto p-2">
                <a class="navbar-brand" href="{% link index.md %}">Navbar</a>
                <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
                    <span class="navbar-toggler-icon"></span>
                </button>
            </div>

            <div class="p-2">
                <div class="collapse navbar-collapse" id="navbarSupportedContent">
                    <div class="navbar-nav">

                        {% for entry in site.data.navigation %}
                        {% if entry.url == current_page %}
                        {% assign current = 'active' %}
                        {% else %}
                        {% assign current = '' %}
                        {% endif %}

                        {% assign sublinks = entry.sublinks %}
                        {% if sublinks %}
                        <li class="nav-item dropdown {{current}}">
                            <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">
                                {{ entry.title }}
                            </a>
                            <div class="dropdown-menu">
                                {% for sublink in sublinks %}
                                <a class="dropdown-item" href="{{ sublink.url | absolute_url }}">
                                    {{ sublink.title }}
                                </a>
                                {% endfor %}
                            </div>
                        </li>
                        {% else %}
                        <li class="nav-item {{current}}">
                            <a class="nav-link" href="{{ entry.url | absolute_url }}">
                                {{ entry.title }}
                            </a>
                        </li>
                        {% endif %}
                        {% endfor %}
                        </ul>
                    </div>
                </div>
            </div>
        </div>
    </div>



</nav>