[lol768]

I'm confused, many of these examples state that they don't work in my browser (Firefox) - but the live demo works fine? Are the demos poly-filled?

[extra88]

Their labeling of feature availability is messed up. It says sibling-index() is widely available when it's not even available in Firefox yet.

[nine_k]

No, it says: "Limited availability".

These green percentage points at the bottom left show how many of the Web audience (IDK by what measurements) runs a browser supporting this feature. A ton of them are even below 50%.

So I suppose it's not "modern CSS", but more like "latest Chrome CSS". Best viewed in Internet Explorer 5.

[Kailhus]

Absolutely. So no thank you, I won't stop writing CSS like it's 2015 if those features aren't at least supported by all latest browsers.