Hi juan1234,

1. Coupon warning message

Use below Custom CSS

.woocommerce-cart .cart-content-wrapper .woocommerce-error:last-of-type{
 background-color: #000;
}

2. Please make sure you synced the strings first before translating WooCommerce, WoodMart Core plugins and WoodMart theme. You can refer to article https://xtemos.com/docs-topic/theme-translation/

In order to change free shipping method, use below Custom CSS

label[for="shipping_method_0_flexible_shipping_single5"]{
	color: #fff;
}

Regards,