CSS behaviors bug report: dark/light switch non-functional

CSS behaviors bug report: dark/light switch non-functional

[Robin H. Johnson]

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I wanted to include a patch, but no obvious way without it being messy
really stood out, so this is only a bug report.

contrib/css describes using the 'prefers-color-scheme' media query
selector, but Gentoo got a report that the selection between light &
dark didn't work.

One of the other devs traced it down to nuances of the HTML link media
attribute: query expressions are not valid in the HTML variant in some
browsers.

This is also mentioned here:
https://stackoverflow.com/questions/69113672/loading-css-based-on-prefers-color-scheme-media-query
> Loading CSS based on any media query expression seems to be out of specification for the media attribute.

As a workaround, I merged the two files with a wrapper, but it feels
sub-optimal, because the entire text gets injected into the PI HTML.

```
@media(prefers-color-scheme: dark) {
 ... #content of 216dark
}
@media(prefers-color-scheme: light) {
 ... #content of 216light
}
```

I think the cleanest solution would be a variant of the above:
clauses, but with @import statements inside them, and making PI-httpd
expose all the CSS Files.

-- 
Robin Hugh Johnson
Gentoo Linux: Dev, Infra Lead, Foundation President & Treasurer
E-Mail   : robbat2@gentoo.org
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Re: CSS behaviors bug report: dark/light switch non-functional

[Eric Wong]

"Robin H. Johnson" <robbat2@gentoo.org> wrote:
> I wanted to include a patch, but no obvious way without it being messy
> really stood out, so this is only a bug report.

Yeah, I've been taking a stab at this in between other things but
not really making progress.
 
> contrib/css describes using the 'prefers-color-scheme' media query
> selector, but Gentoo got a report that the selection between light &
> dark didn't work.

I'm not even sure how that works anymore with fingerprint resistance.

Which browsers + versions + configs are they using?

Will need some testing from others here...

> One of the other devs traced it down to nuances of the HTML link media
> attribute: query expressions are not valid in the HTML variant in some
> browsers.

OK

> This is also mentioned here:
> https://stackoverflow.com/questions/69113672/loading-css-based-on-prefers-color-scheme-media-query
> > Loading CSS based on any media query expression seems to be out of specification for the media attribute.
> 
> As a workaround, I merged the two files with a wrapper, but it feels
> sub-optimal, because the entire text gets injected into the PI HTML.
> 
> ```
> @media(prefers-color-scheme: dark) {
>  ... #content of 216dark
> }
> @media(prefers-color-scheme: light) {
>  ... #content of 216light
> }
> ```

Yeah.

> I think the cleanest solution would be a variant of the above:
> clauses, but with @import statements inside them, and making PI-httpd
> expose all the CSS Files.

I think a safe way is to allow loading any CSS files present in
the same directory as an admin-specified CSS file.  IOW,
	public-inbox.css = /path/to/foo/216dark.css

Will allow autoloading all /path/to/foo/*.css files.


Also, I don't think @import works inside @media,
https://developer.mozilla.org/en-US/docs/Web/CSS/@import says:

| The @import CSS at-rule is used to import style rules from other valid
| stylesheets. An @import rule must be defined at the top of the stylesheet,
| before any other at-rule (except @charset and @layer) and style declarations,
| or it will be ignored.

So I think it'd have to be something like:

@import url('216dark.css') screen and (prefers-color-scheme: light)

If I'm understanding that correctly.

Hopefully I'll be back in a few hours or tomorrow with something
to test...