footer">
      <!-- TODO: rewrite the toggle function. hide the others when one menu is displayed -->
        <a id="menu" class="icon" href="#" onclick="$('#nav-footer').toggle();return false;">
          <i class="fas fa-bars fa-lg" aria-hidden="true"></i> Menu</a>
        <a id="toc" class="icon" href="#" onclick="$('#toc-footer').toggle();return false;">
          <i class="fas fa-list fa-lg" aria-hidden="true"></i> TOC</a>
        <a id="share" class="icon" href="#" onclick="$('#share-footer').toggle()