CSS Scrollbars - for specifying scrollbar styling with CSS, scoped to just enough to get minimally sufficient compat with existing implementations to satisfy existing real world use-cases.
Editor's Draft: https://drafts.csswg.org/css-scrollbars-1
Wiki: https://www.w3.org/wiki/Css-scrollbars
Issues: https://github.com/w3c/csswg-drafts/labels/css-scrollbars-1