sphinx_nervproject_theme/sphinx_nervproject_theme/util/searchbox.html

<div id="searchbox" class="searchbox" role="search">
  <div class="caption"><span class="caption-text">{{ _('Quick search') }}</span>
    <div class="searchformwrapper">
      <form class="search" action="{{ pathto('search') }}" method="get">
        <input type="text" name="q" />
        <input type="submit" value="{{ _('Search') }}" />
        <input type="hidden" name="check_keywords" value="yes" />
        <input type="hidden" name="area" value="default" />
      </form>
    </div>
  </div>
</div>