Syntax features like CSS Nesting can be translated into something older browsers can understand. But other features either can’t be translated, or can only be t

Syntax features like CSS Nesting can be translated into something older browsers can understand. But other features either can’t be translated, or can only be translated in some cases. For example, color-mix(in srgb, red, blue) can be computed as purple at compile time; color-mix(in oklch, var(--a), var(--b)) can be computed iff --a and --b are known to have single static values; and color-mix(in srgb, currentcolor, transparent 50%) fundamentally isn’t known until runtime (even with DOM knowledge, you can’t say “currentcolor is always purple, therefore, &c.”, because the user agent may force colours). So yes, you absolutely still need to care about compatibility. This isn’t about fine-tuning compilation artefacts by hand, this is about browsers lacking features that you’re trying to use.