Toby's Log page 63

@supports is a good way to apply an entire block of styles only if (modern) browsers support a particular property-value combo. There is no similar block-level mechanism for selector support. Selectors are automatically ignored if their values or syntax aren’t recognized by the browser, so they basically already do this at the ruleset level.

Except, sometimes you want to apply styles to other elements that don’t use the selector, but only if the browser supports the selector.