grav-theme-libretic/templates/partials/search.html.twig

<form class="search-box">
    <input type="search" placeholder="Search..." value="{{ query }}" data-search-input="{{ base_url_relative }}{{ config.plugins.simplesearch.route}}/query" />
    <script>
    jQuery(document).ready(function($){
        var input = $('[data-search-input]');

        input.on('keypress', function(event) {
            if (event.which == 13 && input.val().length > 3) {
                event.preventDefault();
                window.location.href = input.data('search-input') + '{{ config.system.param_sep }}' + input.val();
            }
        });
    });
    </script>
    <i class="fa fa-search"></i>
</form>