calibre/manual/templates/searchbox.html

{%- if pagename != "search" and builder != "singlehtml" %}
<div id="searchbox" role="search">
    <form class="search" action="{{ pathto('search') }}" method="get">
      <div style="display: flex">
          <input type="text" name="q" placeholder="{{ search_box_text }}" />&nbsp;
          <input type="submit" value="{{ _('Go') }}" />
      </div>
    </form>
</div>
{%- endif %}