Enable Always On Scrollbars on MacOS Load https://jsfiddle.net/z2da3hec/17/ You will see that it renders almost entirely blue except for the scroll corner which renders plain white. I would expect it to be colour matched to the scrollbar track colour.
It's worth noting this only appears to be an issue with overflow: scroll. When actual scrollbars render the scroll corner correctly matches the track colour. (Not fully dynamically but I will raise a separate issue for that)
<rdar://problem/111589846>
Pull request: https://github.com/WebKit/WebKit/pull/15476
Committed 265687@main (4498c483beb9): <https://commits.webkit.org/265687@main> Reviewed commits have been landed. Closing PR #15476 and removing active labels.