307982 2026-02-16 06:33:05 -0800 REGRESSION (17.4-26): `@scope` with custom-element scope root stops applying to `:scope` and descendants 2026-05-07 09:14:32 -0700 1 1 1 Unclassified WebKit CSS Safari 26 All All RESOLVED DUPLICATE 308330 https://jsfiddle.net/m7dbr8zw/ BrowserCompat, InRadar P2 Normal --- 1 devhassan941 webkit-unassigned ahmad.saleem792 karlcow koivisto webkit-bug-importer oldest_to_newest 2182060 0 devhassan941 2026-02-16 06:33:05 -0800 Summary @scope with a custom-element root works in older Safari/WebKit, but fails in newer WebKit builds. Equivalent non-scoped selectors still work. Minimal repro Save as scope-custom-root-repro.html and open in browser. <!doctype html> <meta charset="utf-8"> <x-shell id="control-root"><span class="child">control child</span></x-shell> <x-shell id="scoped-root"><span class="child">scoped child</span></x-shell> <style> x-shell { display:block; margin:8px 0; } #control-root { color: rgb(0, 128, 0); } #control-root .child { color: rgb(0, 128, 0); } @scope (#scoped-root) { :scope { color: rgb(255, 0, 0); } .child { color: rgb(255, 0, 0); } } </style> <script> customElements.define('x-shell', class extends HTMLElement { constructor() { super(); const r = this.attachShadow({ mode: 'open' }); r.innerHTML = '<slot></slot>'; } }); </script> Steps to reproduce 1. Open file in Safari/WebKit 2. Check computed color of #scoped-root and #scoped-root .child Expected behavior - #scoped-root and .child are red Actual behavior in newer WebKit - #scoped-root and .child remain black (scoped block not applied) Control - #control-root rules apply correctly (green), showing regular selector path is fine Interoperability / version notes - Chromium: works - WebKit 17.4 (Playwright WebKit build): works - WebKit 26.0 (Playwright WebKit build): fails - This suggests a regression in newer WebKit 2182070 1 webkit-bug-importer 2026-02-16 07:41:24 -0800 <rdar://problem/170474720> 2182110 2 ahmad.saleem792 2026-02-16 10:00:36 -0800 *** Safari Technology Preview 237 *** scope child <- it is not red. *** Chrome Canary 147 *** scope child <- it is red. *** Firefox Nightly 149 *** scope child <- it is red. 2204437 3 ahmad.saleem792 2026-04-25 06:31:37 -0700 WebKit ToT (312015@main) matches Chrome Canary 149.0.7809.0 (Official Build) canary (arm64) and have `scope child` as red. So it is fixed now on ToT but still broken on Safari Technology Preview 242. 2208608 4 koivisto 2026-05-07 09:14:32 -0700 *** This bug has been marked as a duplicate of bug 308330 ***