<form role="search" method="get" id="searchform" class="searchform" action="<?php echo esc_url( home_url( '/' ) ); ?>">
  <input class="form-control" name="s" type="search" placeholder="<?php _e( 'Start your search', 'span' );?>">
  <button class="search-btn" type="submit"><i class="fa fa-search"></i></button>
</form>