[css-color-adjust-1] color-scheme should affect embedded iframes #4772
Description
When a site contains iframes that specify their color-scheme either via the meta tag or the CSS property, the default text color changes, however, the background color is transparent, see this demo and note how the screenshot (Chrome Canary 82 left, Safari Tech Preview 100 right) shows the disappearing heading (white on white):
(Chrome doesn't implement form element darkening yet.)
If, however, one loads one of the embedded iframes in isolation (demo), things work as expected and the background is dark (again Chrome left, Safari right):
As discussed with @chrishtr in an offline thread, color-scheme should arguably also affect embedded iframes and render them as if they were the root document.
Spec links:
- https://drafts.csswg.org/css-color-adjust-1/#color-scheme-prop
- https://drafts.csswg.org/css-color-adjust-1/#color-scheme-meta
CC: @lilles