pybiru on "[Plugin: Contact Form 7] How do I customize the style/html of validation errors, success/error messages"

I just wanted to make the borders of the inputs red. Some CSS knowledge required.

Hide standard error messages with...

.wpcf7-not-valid-tip{
  display: none !important;
}

Then if the form is invalid, it adds a class "invalid" to the form itself. So then to make fields that are invalid highlighted in red...

form.invalid input.wpcf7-not-valid{
  border:1px solid red;
  background:#f0e3e3;
}

That's one solution anyway.