[Webkit-unassigned] [Bug 244494] New: Scrollbar doesn't update on CSS color-scheme change

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=244494

            Bug ID: 244494
           Summary: Scrollbar doesn't update on CSS color-scheme change
           Product: WebKit
           Version: Safari 15
          Hardware: Mac (Apple Silicon)
                OS: macOS 12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: maros.pis at gmail.com

Created attachment 461974

  --> https://bugs.webkit.org/attachment.cgi?id=461974&action=review

Bug example

When "color-scheme" change from "light" to "dark" and vice versa colors of scrollbar aren't updated. It seems like element reflow/repaint is missing. I created jsfiddle which displays this issue. Colors are updated only after hover over scrollbar or in case scrollbar is rendered due "overflow:auto" force-reflow hack fix it too but it didn't work if scrollbar came from "overflow:scroll".

Steps to reproduce in example
1. Open in Safari
2. Click "Toggle theme - dark" button
  - page should change background color to blue but scrollbars should stay same as on yellow (white bg with grey slider)
3. Click "Force reflow"
  - top block with Lorem ipsum should change scrollbar colour to be semi-transparent (low opacity dark bg and grey slider), but lower block with horizontal & vertical scrollbar should stay same
4. Hover over scrollbars of bottom Lorem ipsum
  - scrollbars should turn to semi-transparend but bottom right edge should stay white


Example in attachement & in JSFiddle https://jsfiddle.net/marospistej/vj9tf2on/41/

Issue is only present on Safari, all Chrome, FF change scrollbar color as expected even without reflow

Expected behaviour:
When "color-scheme" change scrollbars should update

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