Get the book. CSS Similarly, the CSS doesn't need to change very much; we just turn the :invalid pseudo-class into a real class and avoid using the attribute selector that does not work on You mentioned it as an option. This kind of validation is necessary when the data entered by the user is tied to additional data stored on the server side of your application.
You need to determine how to validate your data: string operations, type conversion, regular expressions, etc. This results in a slow response from the server. Error message is missing and input fields are colored with pastel red that is not easy to spot. Your message has been sent to W3Schools.