Automatic Method: You should now simply use: https://jigsaw.w3.org/css-validator/check/referer?profile=css3. Manual Method: Typically, if we want to link dynamically to the W3C Valid CSS page, we use this link: https://jigsaw.w3.org/css-validator/check/referer That’s perfect if you’re using all CSS2.1, as that’s the default checker, but if you implement even one CSS3 style, you’ll fail validation. So, we can no … How to Link to the W3C CSS3 Validation Page