WPT details: This feature updates the design of chrome's scrollbars and doesn't modify any web API. The changes in layout are included in all tests that show scrollbars, due to the nature of how WPT evaluates results. Fluent scrollbars are already enabled by default in tests, and only a test that checked fonts was rebased because it relied on a screenshot that showed scrollbars (wpt/html/syntax/charset/without-inheritance.html).
This feature modernizes the Chromium scrollbars (both overlay and non-overlay) on Windows and Linux to fit the Windows 11 Fluent design language. Non-overlay Fluent scrollbars will be enabled by default in Linux and Windows. This change applies to Linux as well because Chromium's Linux scrollbar design has historically been aligned with what ships on Windows. How to expose enabling overlay Fluent scrollbars is still being decided. Visual spec: https://docs.google.com/document/d/1haDpb1QIh2PaLwsQD1i4WHFq_5_jSK3XK9lhgSs4WkM/edit?usp=sharing Design doc: https://docs.google.com/document/d/1GCmz2nbJV1XiopoLHnlrVaHCjhQMdiyDfPN_a22OIjU/edit?usp=sharing Intent to implement: https://groups.google.com/a/chromium.org/g/blink-dev/c/SomQdLx6aEk