Set Scrollbars to Always On. Load https://jsfiddle.net/fj8L4g90/ You will see that the scroll corner is still white in the top square. When it should be blue like on the lower one. Note this is not a duplicate of https://bugs.webkit.org/show_bug.cgi?id=258482 as that's specifically to do with overflow scroll.
Created attachment 466818 [details] Screenshot of running the linked jsfiddle This is the result of running this jsfiddle on the branch that addresses https://bugs.webkit.org/show_bug.cgi?id=244494
Managed to fix this as part of the PR for 244494