I think that's an original issue though.

Accessibility certainly requires a content-first approach, I agree with you there. If you view each part of an application solely in terms of what it looks like to a sighted user, it's easy to miss the subtleties of what the underlying structure ought to be.

But when you start layering on the presentation, you're still generally binding that presentation layer tightly to the current content. If you, for example, were to restructure the links in the Zen Garden footer for some reason, most of the styles would break because they're bound to the current structure of the content. The separation you talk about only exists in one direction.

By comparison, when I talk about separation and decoupling in terms of code, I mean that there is a single, explicit, and tight API that acts as a clear boundary between two units. By explicit, I mean that I've designed the units specifically so that they expose this API - this is almost exactly the opposite of what I should be doing with content and presentation, as you point out! By tight, I mean that the API is as minimal as I can make it - two units interacting via an API need to understand nothing of each other except that API, and that API is as small as possible.

None of that is happening when it comes to the interaction between content and presentation. The content is not explicit - I'm actively trying to write the content for the design, which precludes making it an explicit API surface. Nor is the content tight - again, I want to build the content without worrying about how I will layer the design on top, and I don't want to limit myself to just a small surface area here.

So to me, it makes sense to see the content and presentation as being coupled together, even if that coupling ideally goes in one direction only. And if two systems are coupled together, it makes sense to do that explicitly by co-locating those systems. Therefore, I tend to prefer systems like Tailwind that let me apply the presentation layer directly in the content layer. (In practice, I mostly prefer other tools that still let me write real CSS syntax, but Tailwind is pretty damn convenient a lot of the time.)

As an aside, talking about accessibility, I'd forgotten how inaccessible some of the Zen Garden designs are with their addition of extra content in the presentation layer alone.