docs/source/_templates/docs-sidebar.html

<a class="navbar-brand" href="{{ pathto(master_doc) }}">
  <img src="{{ pathto('_static/' + logo, 1) }}" class="logo" alt="logo">
</a>

<form class="bd-search d-flex align-items-center" action="{{ pathto('search') }}" method="get">
  <i class="icon fas fa-search"></i>
  <input type="search" class="form-control" name="q" id="search-input" placeholder="{{ theme_search_bar_text }}" aria-label="{{ theme_search_bar_text }}" autocomplete="off" >
</form>

<nav class="bd-links" id="bd-docs-nav" aria-label="Main navigation">
  <div class="bd-toc-item active">
    {% if "python/api" in pagename or "python/generated" in pagename %}
    {{ generate_nav_html("sidebar", startdepth=0, maxdepth=3, collapse=False, includehidden=True, titles_only=True) }}
    {% else %}
    {{ generate_nav_html("sidebar", startdepth=0, maxdepth=4, collapse=False, includehidden=True, titles_only=True) }}
    {% endif %}
  </div>
</nav>