rtd/sphinx_bootstrap_theme/bootstrap/navbartoc.html

<li class="dropdown">
  <a role="button"
     id="dLabelLocalToc"
     data-toggle="dropdown"
     data-target="#"
     href="#">{{ _(theme_navbar_pagenav_name) }} <b class="caret"></b></a>
  <ul class="dropdown-menu localtoc"
      role="menu"
      aria-labelledby="dLabelLocalToc">{{ toc }}</ul>
</li>