Change style for the zero value coupon

Modify the style of zero value coupons.

if(!function_exists('woo_discount_rules_apply_style_for_zero_price_coupon_method')){
    function woo_discount_rules_apply_style_for_zero_price_coupon_method($style, $coupon){
        //Return the css  as required based on $coupon
    }
}
add_filter('woo_discount_rules_apply_style_for_zero_price_coupon', 'woo_discount_rules_apply_style_for_zero_price_coupon_method', 10, 2);