<form method="get" action="<?php echo esc_url( home_url( '/' ) ); ?>" class="dropdown-menu" aria-labelledby="searchDropdown">
    <input type="text" name="s" placeholder="<?php esc_html_e('Search...', 'univarsal');?>">
    <button><i class="fa fa-search" aria-hidden="true"></i></button>
</form>