Functions Code

// dropdown filter
class dropdown extends Walker_CategoryDropdown {

    function start_el(&$output, $category, $depth, $args) {
        $pad = str_repeat(' ', $depth * 3);

        $cat_name = apply_filters('list_cats', $category->name, $category);
        $output .= "\t<option class=\"level-$depth\" value=\"".$category->slug."\"";
        if ( $category->term_id == $args['selected'] )
            $output .= ' selected="selected"';
        $output .= '>';
        $output .= $pad.$cat_name;
        $output .= "</option>\n";
    }
}