Serving a website is different than serving food or providing safety features. Web design can use progressive enhancement and detect available features to use as they are available.

With a website, you can have the "real" layout, but when someone is blocking your JS, you can fallback and still provide content.

We won't get every mobile application working on old browsers, but we can offer something to the end user. Even a page that lets them know they are missing out.

But CSS Nesting? We can have that and a fallback.