css for menu and inserted search box

I have a child theme of simple market and I have inserted a search box at the end using the following code

add_filter(‘wp_nav_menu_items’,’add_search_box’, 10, 2);

function add_search_box($items, $args) {

ob_start();

get_search_form();

$searchform = ob_get_contents();

ob_end_clean();

$items .= ‘<li id=”menu-item-search”>’ . $searchform . ”;

return $items;

}

this works fine in that it is putting the search box there but I wanted it to go to the right of the menu bar. A general look through google for this seemed to indicate that

#menu-item-search {

float : right!important;

}

should work but it doesn’t make any difference?