<form role="search" method="get" class="search-form" action="<?php echo esc_url( home_url( '/' ) ); ?>">
    <div class="input-group">
        <input type="search" value="<?php echo get_search_query() ?>" class="form-control" name="s" placeholder="<?php echo esc_attr_x( 'Search &hellip;', 'larx' ); ?>">
        <span class="input-group-btn">
            <button class="btn btn-primary" type="submit">
                <i class="fa fa-search"></i>
            </button>
        </span>
    </div>
</form>