_layouts/default.html

<!DOCTYPE html>
<html lang="{{ page.lang | default: site.lang | default: "en" }}">
  <head>
    {% include head.html %}

    {% if page.layout == "toc" %}
      <link
        rel="stylesheet"
        href="https://cdn.rawgit.com/afeld/bootstrap-toc/v1.0.1/dist/bootstrap-toc.min.css"
      />
    {% endif %}
    <script src="https://kit.fontawesome.com/d1fda3c658.js" crossorigin="anonymous"></script>
    <title>{{ page.title_bar | default: page.title }}</title>
  </head>
  <body>
    {% include header.html %}

    {% if page.no_container %}
      {{ content }}
    {% else %}
      <div class="container" style="margin-top:1em">
        {{ content }}
      </div>
    {% endif %}
    
    <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
    {% if page.layout == "toc" %}
      <script src="https://cdn.rawgit.com/afeld/bootstrap-toc/v1.0.1/dist/bootstrap-toc.min.js"></script>
      <script>
      $(function() {
      var navSelector = "#toc";
      var $myNav = $(navSelector);
      Toc.init({
      $nav: $myNav,
      $scope: $("h2, h3")
      });
      $("body").scrollspy({
      target: navSelector
      });
      });
      </script>
    {% endif %}
  </body>
</html>