Steps to reproduce the issue

1. Go to index.php/registration-form (you may need to enable Account Registration in your Global Configuration)
2. DO NOT focus on any of the fields
3. Using your browser inspector, create a new rule and inject the following CSS:

input:invalid {
  background-color: #f00
}

Expected result

Despite being required, the background colour of the fields should not be applied, because they shouldn't be invalid by default

Actual result

All the fields have a red background