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Table of Contents
How :invalid Works
How :valid Works
Common Use Cases and Tips
Home Web Front-end CSS Tutorial What is the `:invalid` and `:valid` pseudo-classes?

What is the `:invalid` and `:valid` pseudo-classes?

Jul 26, 2025 am 04:27 AM

The :invalid and :valid pseudo-classes in CSS are used to style form elements based on their validation state. 1. :invalid targets fields that don’t meet validation rules such as required fields being empty or incorrect email formats, allowing developers to highlight errors visually. 2. :valid applies to elements that pass validation criteria, enabling positive feedback like green borders. 3. Both pseudo-classes apply styles immediately on page load, though :user-invalid can be used for user interaction-based styling. 4. These classes work only on form elements with constraints like required, min, or max. 5. While they enhance UX with real-time feedback, they should not replace server-side validation.

What is the `:invalid` and `:valid` pseudo-classes?

When you're working with form validation in CSS, the :invalid and :valid pseudo-classes are super handy. They let you style form elements based on whether their current value meets the validation rules defined in your HTML — like required fields, email formats, or min/max values.

What is the `:invalid` and `:valid` pseudo-classes?

How :invalid Works

:invalid applies to any form element that doesn't meet its validation criteria. For example, if a field is required but empty, or an email field has the wrong format, it will match :invalid.

You can use this to give users visual feedback right away without JavaScript:

What is the `:invalid` and `:valid` pseudo-classes?
  • Highlight input borders in red
  • Show error messages or icons
  • Add tooltips or helper text when the field is invalid
input:invalid {
  border-color: red;
}

Keep in mind, though, that browsers usually apply :invalid as soon as the page loads. That means required fields show up as invalid even if the user hasn’t interacted with them yet. If you don’t want that, you’ll need to combine it with other techniques like checking for :user-invalid, which only triggers after the user has tried submitting or interacting with the field (but browser support is still catching up).

How :valid Works

Opposite of :invalid, the :valid pseudo-class targets form elements that currently pass all their validation checks.

What is the `:invalid` and `:valid` pseudo-classes?

This is useful for giving positive feedback:

  • Green borders or checkmarks
  • Confirmation messages
  • Enabling a submit button only when all fields are valid
input:valid {
  border-color: green;
}

Like :invalid, :valid also applies immediately on page load. So if a field isn’t required and is empty, it might be considered valid by default. This behavior makes sense because an empty optional field isn’t technically invalid — just not filled out yet.

Common Use Cases and Tips

Here are some practical ways developers use these pseudo-classes:

  • Real-time form feedback – Users get immediate visual cues as they type.
  • Styling error messages – You can pair :invalid with adjacent labels or error containers.
  • Conditional styling – Style parent containers or other related elements using general sibling or child combinators.
  • Accessibility enhancements – Combine with ARIA attributes to make forms more usable for screen readers.

A few things to keep in mind:

  • These pseudo-classes only work on form elements with validation constraints (like required, pattern, min, max, etc.).
  • Styling too aggressively can interfere with browser defaults or accessibility features.
  • Always back up client-side validation with server-side checks — CSS-only validation doesn’t prevent bad data from being submitted.

So basically, :invalid and :valid offer a quick and effective way to visually reinforce form validation, making your web forms more user-friendly without needing JavaScript. Just remember, while they’re great for UX, they shouldn’t replace actual data validation on the backend.

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