docs/source/_templates/searchbox.html

{%- if pagename != "search" and builder != "singlehtml" %}
   <form class="search" action="{{ pathto('search') }}" method="get" role="search">
      <input type="text" class="search__text" name="q" aria-labelledby="searchlabel" placeholder="Search Documentation" />
   </form>
{%- endif %}