>
Nesting in CSS became broadly supported in Chromium and other evergreen browsers a few months ago.Firefox hasn’t shipped it yet. https://caniuse.com/css-nesting shows it landing in 117 next month.
> Even now, it’s not supported by older versions of iOS/mobile Safari which could easily be 15-20% of a large US based websites’ traffic.
Yeah, actual global support is probably still below ⅔—caniuse.com is showing global support at 72.89%, and its methodology is hopelessly broken for mobile browsers (treats all mobile Chrome/Android WebView as the latest version, which is wildly wrong), quite apart from excluding browsers that block the StatCounter script, leading to particularly heavy undercounting of Firefox and general undercounting of more conservative or unusual configurations; so the true numbers on newish features are always much worse than it suggests.
For these sorts of features, if all browsers ship around the same time, you’ll normally want to wait for about another two years before you start depending on it. (When shipped out of sync, it depends—you’ll encounter two-year-old Safari more commonly than six-month-old desktop Chrome, for example.)