Scrollbars in macOS and iOS ports can change color depending on the page, using dark scrollbars on dark pages and light scrollbars on light pages. We should support that too. See the patch.
Created attachment 433207 [details] Patch
Test case: https://blog.ergaster.org/ https://webkit.org also triggers a dark scrollbar.
Comment on attachment 433207 [details] Patch LGTM. Maybe Carlos Garcia might want to review this before landing, though?
Committed r279782 (239549@main): <https://commits.webkit.org/239549@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 433207 [details].