312074 2026-04-11 20:48:32 -0700 document.styleSheets and shadowRoot.styleSheets incorrectly include adopted style sheets 2026-04-15 23:19:48 -0700 1 1 1 Unclassified WebKit New Bugs WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED https://github.com/web-platform-tests/wpt/pull/59255 InRadar, WPTImpact P2 Normal --- 1 ahmad.saleem792 ahmad.saleem792 webkit-bug-importer oldest_to_newest 2199344 0 ahmad.saleem792 2026-04-11 20:48:32 -0700 Per the CSSOM spec (§6.2 CSS Style Sheet Collections), the "document or shadow root CSS style sheets" list should only contain: 1. CSS style sheets created from HTTP Link headers 2. CSS style sheets associated with the DocumentOrShadowRoot (i.e., from <style> and <link> elements), in tree order Adopted style sheets (from adoptedStyleSheets) are only included in the "final CSS style sheets" list, which is a separate concept used for style resolution. The styleSheets attribute (StyleSheetList) should reflect the "document or shadow root CSS style sheets", not the "final CSS style sheets". WebKit currently includes adopted style sheets in StyleSheetList, causing document.styleSheets and shadowRoot.styleSheets to report incorrect lengths and entries when adoptedStyleSheets is non-empty. Steps to Reproduce: <style id="sheet1">body { width: 50%; }</style> <script> const sheet = new CSSStyleSheet(); document.adoptedStyleSheets = [sheet]; console.log(document.styleSheets.length); // Expected: 1, Actual: 2 </script> Expected: document.styleSheets.length is 1 (only the <style> element sheet). Actual: document.styleSheets.length is 2 (includes the adopted sheet). Root Cause: In Source/WebCore/style/StyleScope.cpp, collectActiveStyleSheets() appends adopted style sheets to both sheets (used for style resolution — correct) and styleSheetsForStyleSheetsList (backing the DOM-visible StyleSheetList — incorrect). Spec Reference: https://drafts.csswg.org/cssom/#css-style-sheet-collections Failing WPT Tests: - css/cssom/StyleSheetList-constructable.html - css/cssom/StyleSheetList-constructable-with-style-recalc.html --- This also affects shadowRoot.styleSheets since the same code path in StyleScope is shared by both Document and ShadowRoot. 2199345 1 webkit-bug-importer 2026-04-11 21:09:19 -0700 <rdar://problem/174583340> 2199346 2 ahmad.saleem792 2026-04-11 21:11:56 -0700 Pull request: https://github.com/WebKit/WebKit/pull/62572 2199678 3 ews-feeder 2026-04-13 04:53:51 -0700 Committed 311074@main (2dd7e967bacc): <https://commits.webkit.org/311074@main> Reviewed commits have been landed. Closing PR #62572 and removing active labels. 2200970 4 ahmad.saleem792 2026-04-15 23:19:48 -0700 Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/59255