[rvense]

> It's about separating concerns to allow extensibility of one aspect of the component without having to worry about the other parts of the system.

Right, and I don't see the HTML and the CSS as separate concerns when the HTML describes a GUI, not a document. There being two languages in play is a historical detail that as developers we have to tackle in the best way. I don't believe that it's some sort of holy spirit we have to respect.

For my money, separation of concerns is things like where do I put my mutable state, which part of the application talks to the network, etc.

> but what if I'd like to have multiple styles

I have to say that's not a thing I've ever needed to worry about. I'm worried about things turning into a big pile of goop. The old approach too often devolved into making a separate class for each tag. Starting with repetition and noticing patterns that then get factored out is a better approach for me.

I will say, though, that in Tailwind it absolutely would be workable to give e.g. colours a semantic name - like primary and secondary - and then map those to whatever you want, including CSS custom properties. So you absolutely can implement both build-time and runtime theming at that level if you want, where you just need to change configuration options or a set of properties.

> What do I have to gain from Tailwind if I am using already SASS as the preprocessor and a good library of "utility classes" that can be @imported/@use'd/@apply'd to the document without touching the HTML?

Again, I'm not afraid of touching the HTML, that's not a goal for me. In my work, any change of any consequence is going to involve both HTML, CSS, and JS anyway. I am much more afraid of accumulating cruft in poorly-maintained CSS files.

Tailwind's utility classes are pretty fantastic - for instance, you can define a colour palette and they also become usable in gradients - so they're a good place to start. I also like that it's basically real CSS because that forces developers to learn, which will lead to better layouts. And yes, it will in some cases lead to the same set of classes as a semantic approach, because sometimes that classes are what makes sense. But the thing is, how do you arrive at that set of classes, and what do you do with the edges and boundaries and all the glue you need. Tailwind provides an extremely usable starting point and a good thought pattern for building the type of apps I do.

[rglullis]

> Right, and I don't see the HTML and the CSS as separate concerns when the HTML describes a GUI, not a document.

You know that you can create themes in GTK (a Desktop GUI) using CSS nowadays, right? Whether a document or a GUI, behavior (how it works) and presentation (how it looks) are still separate concerns.

> (Multiple styles)'s not a thing I've ever needed to worry about.

Yeah, others have though - both as consumers and as integrators. If you are okay with the idea of re-inventing wheels every time you want to have a different color, plenty of people are not.

> I'm not afraid of touching the HTML

It's not a matter of being afraid to touch HTML. It's a matter of not being able to! Whether in terms of ability (some marketing person that is putting together a wordpress or Shopify store and can only go with different artifacts provided to them) or from the nature of the source code (e.g, imagine you want to make a RSS/Atom feed reader, embed a Tweet on your site with a custom styling or use an OSM tile editor), if you are not able to touch the code but you can select different styles, then it is fundamental that the data is separated from the style definition.

You might not think that this is important for you to do your job, but I think that is extremely short-sighted. What made the web as interesting as an application platform was the idea that the user agent could be extended. It is in our interests as users to keep the web open and able to be tinkered with, and the easier it is to separate the layers that people want to improve, the better.

[rvense]

> You know that you can create themes in GTK (a Desktop GUI) using CSS nowadays, right?

Does GTK offer CSS layouts? Do I describe the elements of the UI using HTML? As far as I know they just use a subset of CSS - aren't the selectors predefined by the framework? I don't recall, exactly. But GTK provides an entirely different set of primitives, I don't think it's the same problem at all if you're just providing fonts and colours. Again, I'm talking about something rather specific, creating complex, desktop-like user interfaces using HTML and SPA frameworks.

> behavior (how it works) and presentation (how it looks) are still separate concerns.

Yeah, but I wouldn't say that that distinction maps to the distinction between CSS and HTML at all, not in my context. HTML, especially document structure, is also presentational. That's really what I mean when I say it's not a "document".

And any way, no matter which approach (and platform, I'd wager) you use, if you want to completely restyle a complex GUI application like what I'm writing in the way you could restyle HTML documents like the Zen garden, you're looking at some serious engineering effort in keeping the so-called behavioural HTML and Javascript in check and documented. It won't just be about how you handle the CSS, it'll be about how you handle everything.

> Yeah, others have though - both as consumers and as integrators. If you are okay with the idea of re-inventing wheels every time you want to have a different color, plenty of people are not.

I actually feel like I have better control of my colours with Tailwind than I ever did. Currently I'm using a limited selection specified in the Tailwind theme. They have names like $adjective-$colour, so it'd be weird to change them, but if that's important to you that things are themable, as I stated, you can put in the effort to set it up with semantic names and make them customizable at build time or at run time. I still think you'd have a better experience than making separate classes for every tag and reimplementing that for each theme.

> It's not a matter of being afraid to touch HTML. It's a matter of not being able to! ...

And all of these things you list are not what I do. The examples that you list have a different set of trade-offs. I'm not embedding other people's code in my GUI, and I don't expect them to take a random chunk of my application and put them into theirs. OpenDoc was a fun idea, but it didn't take off.

> What made the web as interesting as an application platform was the idea that the user agent could be extended.

I don't really know about that in the general case, I think there are more reasons than that, but in the specific case I'm certain it's wrong. The reason my company is doing what it's doing on the web is 100% about distribution. Arguably, the web stack isn't even that good for making the kind of UIs I do - but if we did what we're doing in Java, we wouldn't get any users (or investors).

I totally agree with you about openness, but openness in my space means providing good APIs and integrations with other services, not allowing user stylesheets. A user stylesheet for my app would mean a twenty page list of weirdly interdependent CSS selectors, and the end result for someone who implemented it would be something like a colour theme that only works for app. Explain to me who would want that.