ese-website/_includes/header.njk

<header>
  <div class="header-container content">
    <a id="header-logo" href="{{ "/" | locale_url }}" title="home">
      <img alt="ESE {{year}} Logo" src="/static/ESELogo24.svg">
    </a>
    <nav id="mainNav">
      {% set navPages = collections.mainNav | pageLang | eleventyNavigation %}
      <ul>
        {%- for entry in navPages -%}
        <li>
          <a class="nav-item {%- if entry.url == page.url %} active{% endif %}"
            href="{{ entry.url }}">{{ entry.title }}</a>
        </li>
        {%- endfor %}
        <li>
          <a class="nav-item-stream" href="https://stream.ifsr.de/" target="_blank" rel="noopener">Stream</a>
        </li>
      </ul>
    </nav>
  </div>
</header>

{% css %}
  {% include "header.css" %}
{% endcss %}