Tests like [1] fail in WebKit. The css-contain spec[2] has been changed after the CSSWG resolution in [3] stopping propagation from body to viewport for non-none used containment on root and body. [1] https://wpt.fyi/css/css-contain/contain-body-bg-001.html [2] https://drafts.csswg.org/css-contain-1/#c3 [3] https://github.com/w3c/csswg-drafts/issues/5913
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<rdar://problem/83151391>
This was fixed by r244980.