How to make a CSS file valid?

Question

I have a CSS file that uses CSS3 properties (opacity and -moz-* and -webkit-* ones). Of course, it doesn't validate as CSS 2.1. Not a big deal, but nevertheless is it possible to make it valid CSS 2.1?

Answer 1

Not without not using those selectors, no.

Answer 2

Illegal values or unknown properties are being ignored. So unless you have a syntax error, you can use those values/properties.

Or do you want to have a valid CSS 2.1 stylesheet just to put a badge on your website?

Answer 3

It is not possible to validate an invalid CSS.

A CSS with not standard selectors is not valid.

Answer 4

Use all CSS3 properties in another css sheet, and validate that without CSS3 :)