li>
<li class="nav-item dropdown">
  <button class="nav-link dropdown-toggle" type="button" id="dropdown-urls" data-bs-toggle="dropdown" aria-expanded="false" aria-haspopup="true">URLs</button>
  <ul class="dropdown-menu dropdown-menu-end" aria-labelledby="dropdown-urls"><li><a class="external-link dropdown-item" href="https://cellcarta.com/">CellCarta</a></li>
    <li><a class="external-link dropdown-item" href="https://www.ensembl.org/index.html">BiomaRt</a></li>
    <li><a class="external-link dropdown-i