https://drafts.csswg.org/css-scrollbars-1/#scrollbar-color Syntax is "auto | <color>{2}".
Pull request: https://github.com/WebKit/WebKit/pull/14597
<rdar://problem/110426805>
Committed 265313@main (581332fbe816): <https://commits.webkit.org/265313@main> Reviewed commits have been landed. Closing PR #14597 and removing active labels.