[Webkit-unassigned] [Bug 281131] New: Immediate crash when WebComponents are combined with global styles & container queries.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=281131

            Bug ID: 281131
           Summary: Immediate crash when WebComponents are combined with
                    global styles & container queries.
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: iOS 18
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: marco at mattes.dev
                CC: koivisto at iki.fi

Created attachment 472875

  --> https://bugs.webkit.org/attachment.cgi?id=472875&action=review

Crash Sample Component

The following issue occurs with Safari 18 on all platforms, including Mac, also Technology Preview. 

When using container queries, I noticed a malfunction that I cannot further isolate. The combination of container queries, WebComponents, and (this is where I get stuck) the application of irrelevant CSS causes the page to crash.

I have isolated a Stackblitz sample and partially narrowed down the problem. https://stackblitz.com/edit/stackblitz-starters-gxvbz9?file=index.html

Steps to Reproduce:
1. Open the provided Stackblitz or sample-crash.html sample in Safari 18.
2. Ensure lines 7 to 9 are active.
3. Observe the page crash a few seconds after loading.

The page crashes a few seconds after loading with no error message or indication of the cause. There is no apparent connection between the responsible CSS block and the WebComponent in the example.

Additional Information:
- The issue does not occur when CSS lines 14-20 are commented out.
- The problem seems to be related to the interaction between container queries and WebComponents.
- `.ux-button--no-border:not(:active):not(:disabled):hover ux-icon`==> crashed immediately 
- `.ux-button--no-border:not(:active):not(:disabled):hover > ux-icon` ==> works

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