[mediaqueries-5] active vs inactive window states

[fantasai]

In #4579 we discussed the distinction between ::selection and ::inactive-selection and concluded on removing ::inactive-selection and maybe adding a media query for the active state of the window. Filing this issue as follow-up.

[css-meeting-bot]

The CSS Working Group just discussed [mediaqueries-5] active vs inactive window states, and agreed to the following:

• RESOLVED: Add window-focus: active | none, active for print, behavior matching JS focus/blur events on window, bikeshed names later

The full IRC log of that discussion

<Frances> fantasai: We have ::selection vs ::inactive-selection, wedecided to have a separate media query. What should it be called?
<Frances> Tab: Windows state vs active and inactive for the values
<Frances> Florian: Is there a tab to not focus on multiple windows?
<Frances> Tab: Javascript doesn't expose additional states
<fantasai> window-focus: active | none
<fantasai> window-focus: active | inactove
<Frances> fantasai: Could have an alias for inactive, do not need none on top of it.
<Frances> Florian: Could do something else
<kbabbitt> Wondering which value would take effect in print media
<Frances> Rossen: In overloaded, it could be confusing on the actual focus inside of a window for accessibility.
<schenney> We already support ::selection:window-inactive and ::selection:window-active in Blink
<fantasai> kbabbitt, good question. I'd say active
<schenney> I would drop those if we have a media query.
<fantasai> yes
<Frances> Kevin: Which value would take in affect when considering such as none or active, in a default-ish state?
<Frances> Florian: Need to have a contraster.
<Frances> fantasai: Is it a view focus or a viewport focus? Or an iframe?
<TabAtkins> In JS, the state is exposed via "blur" and "focus" events on window
<Frances> Florian: It is in javascript, let's not be different in javascript.
<Frances> Rossen: Any additional thoughts? No objections
<fantasai> RESOLVED: Add window-focus: active | none, bikeshed later
<Frances> PROPOSAL: Add window-focus: active or none matching behavior of javascript in imprint behavior and matching