wagtail/docs/_templates/searchbox.html

{%- if builder != "singlehtml" %}
<div id="searchbox" class="" role="search">
    <form id="search-form" action="{{ pathto('search') }}" autocomplete="off" method="get">
        <input class="form-control p-3 h-100" type="text" name="q" placeholder="Search" aria-label="Search" id="searchinput" />
        <input type="submit" style="visibility:hidden;position:absolute">
    </form>
</div>
{%- endif %}