The :user-invalid
CSS pseudo-class represents any validated form element whose value isn't valid based on their validation constraints, after the user has interacted with it.
The :user-invalid
pseudo-class must match an :invalid
, :out-of-range
, or blank-but :required
element between the time the user has attempted to submit the form and before the user has interacted again with the form element.
Note: The pseudo-class behaves in the same way as the non-standard :-moz-ui-invalid
pseudo-class.