<a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" data-bs-toggle="dropdown" aria-expanded="false">
    Vignettes
     
    <span class="caret"></span>
  </a>
  <ul class="dropdown-menu" role="menu"><li>
      <a href="https://www.youtube.com/watch?v=UXKYqpAo6cs" class="external-link">Video presentation of package bigstatsr</a>
    </li>
    <li>
      <a href="https://privefl.github.io/bigsnpr/articles/exo.html" class="external-link">Exercise</a>
    </li>
    <li>
      <a href="../a