Native HTML form validation (using attributes like `required`, `type="email"`, or a `pattern`) can be styled directly with the `:valid` and `:invalid` CSS pseudo-classes, giving instant visual feedback without any JavaScript.
Customize the border colors for valid and invalid states, then try typing in the live preview input to see the styling respond in real time as the browser's native validation kicks in.
Once it looks right, copy the CSS using the `:valid` and `:invalid` pseudo-classes, which apply automatically based on the input's `type`, `required`, `pattern`, or other native HTML validation attributes you've set.
Because everything runs locally in your browser, results appear instantly and nothing you type or upload is ever sent to a server.
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Frequently asked questions
Does this require JavaScript?
No, this uses pure CSS pseudo-classes that respond to the browser's built-in HTML5 form validation — no JavaScript is needed for the basic valid/invalid styling.
Why does an empty required field sometimes show as invalid immediately?
By default, :invalid can match an empty required field right away; many developers combine it with the :placeholder-shown or :focus pseudo-classes to delay showing invalid styling until after the user has interacted with the field.