See https://wpt.fyi/results/css/cssom/cssom-getPropertyValue-common-checks.html?diff&filter=ADC&run_id=5133309367025664&run_id=5150860515999744 Bisecting didn't get narrower than 267680@main...267651@main, but my guess is 267658@main (bug 261089).
<rdar://problem/117690856>