Well, the W3C validator also has issues which do not help. For example, Wikipedia doesn't validate [0] because its CSS has "aspect-ratio: 1" which looks ok to

Well, the W3C validator also has issues which do not help. For example, Wikipedia doesn't validate [0] because its CSS has "aspect-ratio: 1" which looks ok to me regarding the spec [1]. [0]: https://jigsaw.w3.org/css-validator/validator?profile=css3svg&usermedium=all&vextwarning=true&uri=https://en.wikipedia.org/ https://jigsaw.w3.org/css-validator/validator?profile=css3sv... [1]: https://w3c.github.io/csswg-drafts/css-values-4/#ratio-value https://w3c.github.io/csswg-drafts/css-values-4/#ratio-value