[mediaqueries-5] Add language about how the browser obtains prefers-color-scheme from the OS

[prarsena]

In mediaqueries-5/#prefers-color-scheme, would it be appropriate to provide details about how the browser obtains information from the device about the user's color preference?

For example:

The method by which the user expresses their preference can vary. It might be a system-wide setting exposed by the Operating System, or a setting controlled by the user agent.

Could this type of language be added:

Information sent from the operating system or the user agent that contains a Sec-CH-Prefers-Color-Scheme Client Hint header (which also supports the "dark" / "light" values) that can be used by the prefers-color-scheme media feature to tailor the response to the client’s preferences accordingly.

Not to get too into the weeds, but I'm also searching for documentation about how the browser communicates with the OS, if anyone knows of resources for that.

[Loirooriol]

UA-OS communication is outside of the scope of CSS.

Also I wouldn't tie prefers-color-scheme to a HTTP header, because the user might change the setting after loading the page. It should be possible to update the media query without requiring a reload with different HTTP headers.