Bug 304555

Safari 26.2 now resolves container-name matching regardless of origin, a discrepancy remains: named style container queries defined on :host are not applied to slotted elements. While unnamed queries were recently fixed for the composed tree, https://github.com/WebKit/WebKit/commit/a20439aa1afd56e3b8e0f4af7c899ac98237fa3d, the same logic fails in Safari when a container-name is involved. Currently, ✅Chrome correctly evaluates the query, but ❌Safari (26.2 and Safari Technology Preview 234) requires the container to be defined in the Light DOM to work. Reproduction: https://lit.dev/playground/#gist=8601556f4a13e49eb85743791f21157d Steps to reproduce: 1. Open the playground in **Safari** and **Chrome**. 2. Observe that in Safari, the background color is **not** applied to the slotted element. 3. In `index.html`, uncomment the following block: ```css parent-element { /* container-name: slotted; */ } ``` 4. Notice it now works in Safari. This confirms the issue only exists when the container is defined via `:host` in the Shadow DOM. - Expected Behavior: Slotted elements should resolve container queries against a named container defined on the `:host` - Actual Behavior (Safari): Slotted elements ignore named containers defined on `:host` References - Related Fix: https://github.com/WebKit/WebKit/commit/a20439aa1afd56e3b8e0f4af7c899ac98237fa3d - Relevant Commit: https://github.com/WebKit/WebKit/commit/efd4ebe98cab2bbb385ffe1e1e40d3870917727b - Container-names are tree-scoped: https://bugs.webkit.org/show_bug.cgi?id=289868