305886 2026-01-20 17:05:12 -0800 ::part(range)::-webkit-slider-thumb can not be an anchor element 2026-01-28 17:53:30 -0800 1 1 1 Unclassified WebKit Layout and Rendering Safari Technology Preview Mac (Apple Silicon) macOS 26 NEW InRadar P2 Normal --- 1 jamesnw webkit-unassigned bfulgham fantasai.bugs karlcow kiet.ho simon.fraser webkit-bug-importer zalan oldest_to_newest 2173513 0 jamesnw 2026-01-20 17:05:12 -0800 ::-webkit-slider-thumb can be used as an anchor element, but it appears not possible when the range input is in a shadow DOM. Minimal reproduction- <styles-outside> <template shadowrootmode="open"> <input type="range" part="slider"></input> <div part="label">shadow, styles outside</div> </template> </styles-outside> <style> styles-outside::part(slider)::-webkit-slider-thumb { anchor-name: --in; } styles-outside::part(label) { position: absolute; position-area: end; position-anchor: --in; } </style> I've tested that you can select the thumb with `inline-demo::part(slider)::-webkit-slider-thumb` for other styles. Styles inside the shadow DOM can make the thumb a valid anchor. Codepen- https://codepen.io/jamessw/pen/qENmzNq/fdfcc35d41d206e88091af42ee2e8f90. This works in Chrome, but can't be expected to work in Firefox given the non-standard ::-webkit-slider-thumb. 2175609 1 webkit-bug-importer 2026-01-27 17:06:12 -0800 <rdar://problem/169049096>