css

[mbostock]

Fixes #666. Not sure there’s a lot of value here (especially relative to #597), but it’s easy to do. My silly test case:

```css
body {
  color: hsl(${x}, 50%, 50%);
}
```

```js
const x = Generators.observe((notify) => {
  notify(0);
  const pointermove = (event) => notify(event.clientX);
  addEventListener("pointermove", pointermove);
  return () => removeEventListener("pointermove", pointermove);
});
```

[Fil]

The (very strong) upside of this is that we can add a CSS chapter to the documentation, instead of having CSS support be indirectly implied by the support for HTML in Markdown.

[mbostock]

The downside is that the CSS is rendered client-side and so it’s more likely to cause a FOUC. I think if we fixed the parser I wouldn’t recommend this (though we could also figure out how to do this with server-side rendering so it’s equivalent to a style tag). 🤔

We could definitely document CSS now but we should also be careful not to try to teach everyone web development from scratch.

[mbostock]

We could server-side render the CSS (like we do with PRQL in #1078). And if there are interpolations, we could additionally have JavaScript to update the CSS dynamically (perhaps more selectively than we currently do? like we could only allow interpolations into CSS values rather than arbitrary chunks of CSS).