304347 2025-12-17 11:48:21 -0800 REGRESSION(293848@main): In certain circumstances, -webkit-box-shadow (and perhaps other prefixed and/or cascade-alias properties) does not transition 2026-01-15 11:44:48 -0800 1 1 1 Unclassified WebKit Animations Safari 18 Unspecified Unspecified RESOLVED FIXED https://bugs.webkit.org/show_bug.cgi?id=285900 InRadar P2 Normal --- 1 sam koivisto graouts koivisto webkit-bug-importer oldest_to_newest 2166680 0 477769 sam 2025-12-17 11:48:21 -0800 Created attachment 477769 Transition using box-shadow (works) I am not sure exactly what the requirements are, but in some circumstances, using `-webkit-box-shadow` rather than `box-shadow` will cause a CSS transition not to occur. See two attached test cases. In the one called "Transition using box-shadow (works)", you will see that the transition happens, and there is a visible box shadow. In the one called "Transition using -webkit-box-shadow (broken)", you will see that the transition does not happen, and there is no visible box shadow. 2166682 1 477770 sam 2025-12-17 11:48:55 -0800 Created attachment 477770 Transition using -webkit-box-shadow (broken) 2166692 2 graouts 2025-12-17 12:13:33 -0800 With both tests I see two transitions being started in Safari (one for -webkit-box-shadow, one for box-shadow), whereas Chrome and Firefox only start one (for box-shadow). I'm not seeing what you're seeing. What version of Safari did you test with? 2166881 3 graouts 2025-12-18 01:03:27 -0800 I don't know whether a spec dictates the behavior for aliases here, but it would be nice to align with Chrome and Firefox here and codify this in WPT. 2166963 4 sam 2025-12-18 08:42:19 -0800 Interesting! I was testing with Safari Version 26.1 (21622.2.11.11.9). I will try ToT. 2168093 5 webkit-bug-importer 2025-12-24 11:49:13 -0800 <rdar://problem/167144768> 2171032 6 graouts 2026-01-11 12:35:37 -0800 Hmm, now I see the issue with the "broken" test with STP 234 and 305425@main, trying to identify when this regressed compared to what we shipped in macOS Sequoia 15.6.1 (24G90). My first regression range is 289651@main → 297306@main, will get a more specific regression point tomorrow. 2171033 7 graouts 2026-01-11 13:18:36 -0800 This broke in 293848@main, the fix for bug 285900. 2171132 8 graouts 2026-01-12 02:52:23 -0800 The behavior where two transitions were yielded when `transition-property: all` was used and a property with an alias changed was modified in 304641@main and it now matches Chrome and Firefox where a single transition occurs. Very nice. 2172255 9 koivisto 2026-01-15 10:34:53 -0800 Pull request: https://github.com/WebKit/WebKit/pull/56649 2172274 10 ews-feeder 2026-01-15 11:44:46 -0800 Committed 305660@main (288510351274): <https://commits.webkit.org/305660@main> Reviewed commits have been landed. Closing PR #56649 and removing active labels. 477769 2025-12-17 11:48:21 -0800 2025-12-17 11:48:21 -0800 Transition using box-shadow (works) test-box-shadow-transition.html text/html 1402 sam PCFET0NUWVBFIGh0bWw+CjxodG1sPgo8aGVhZD4KPHN0eWxlPgogIC50cmFuc2l0aW9uaW5nIHsK ICAgIHdpZHRoOiA0MDBweDsKICAgIGhlaWdodDogNDAwcHg7CiAgICBiYWNrZ3JvdW5kLWNvbG9y OiByZWQ7CiAgICB0cmFuc2l0aW9uOiBhbGwgMnM7CiAgfQo8L3N0eWxlPgo8L2hlYWQ+Cjxib2R5 Pgo8ZGl2IGlkPSJ0YXJnZXQiIGNsYXNzPSJ0cmFuc2l0aW9uaW5nIj48L2Rpdj4KPHByZSBpZD0i bG9nIj48L3ByZT4KPHNjcmlwdD4KICBmdW5jdGlvbiBsb2cobXNnKSB7CiAgICBkb2N1bWVudC5n ZXRFbGVtZW50QnlJZCgnbG9nJykuYXBwZW5kKG5ldyBUZXh0KG1zZyArICJcbiIpKTsKICB9Cgog IGZ1bmN0aW9uIHRlc3RfcHJvcGVydHkocHJvcGVydHksIHN0YXJ0LCBlbmQpIHsKICAgIHRyeSB7 CiAgICAgIGxvZyhgU1RBUlQ6IFRlc3RpbmcgJHtwcm9wZXJ0eX1gKTsKCiAgICAgIHZhciBkaXYg PSBkb2N1bWVudC5nZXRFbGVtZW50QnlJZCgidGFyZ2V0Iik7CiAgICAgIGRvY3VtZW50LmJvZHku YXBwZW5kQ2hpbGQoZGl2KTsKCiAgICAgIGRpdi5zdHlsZSA9IGAke3Byb3BlcnR5fTogJHtzdGFy dH1gOwogIAogICAgICBnZXRDb21wdXRlZFN0eWxlKGRpdikubWFyZ2luTGVmdDsKCiAgICAgIGRp di5zdHlsZSA9IGAke3Byb3BlcnR5fTogJHtlbmR9YDsKCiAgICAgIGxvZygiQ0hFQ0tJTkcgRk9S IGVsZW1lbnQuZ2V0QW5pbWF0aW9ucygpIikKICAgICAgaWYgKGRpdi5nZXRBbmltYXRpb25zKCku bGVuZ3RoID09IDApCiAgICAgICAgbG9nKCJOTyBBTklNQVRJT05TIEZPVU5EIik7CiAgICAgIGVs c2UKICAgICAgICBsb2coYCR7ZGl2LmdldEFuaW1hdGlvbnMoKS5sZW5ndGh9IEFOSU1BVElPTlMg Rk9VTkQ6ICR7ZGl2LmdldEFuaW1hdGlvbnMoKX1gKTsKCiAgICAgIGRpdi5hZGRFdmVudExpc3Rl bmVyKCd0cmFuc2l0aW9uc3RhcnQnLCBmdW5jdGlvbihldmVudCkgewogICAgICAgIGxvZygidHJh bnNpdGlvbnN0YXJ0IGZpcmVkOiAiICsgZXZlbnQpOwogICAgICB9KTsKCiAgICAgIGRpdi5hZGRF dmVudExpc3RlbmVyKCd0cmFuc2l0aW9ucnVuJywgZnVuY3Rpb24oZXZlbnQpIHsKICAgICAgICBs b2coInRyYW5zaXRpb25ydW4gZmlyZWQ6ICIgKyBldmVudCk7CiAgICAgIH0pOwoKICAgICAgbG9n KGBgKQoKICAgIH0gY2F0Y2ggKGV4Y2VwdGlvbikgewogICAgICBsb2coYEVYQ0VQVElPTjogJHtw cm9wZXJ0eX0gLS0gJHtleGNlcHRpb259XG5gKTsKICAgIH0KICB9CgogIHdpbmRvdy5hZGRFdmVu dExpc3RlbmVyKCJsb2FkIiwgZnVuY3Rpb24oZXZlbnQpIHsKICAgIHRlc3RfcHJvcGVydHkoImJv eC1zaGFkb3ciLCAiMCAwIDAgcmdiYSgwLCAwLCAwLCAwKSIsICIxMHB4IDVweCA1cHggYmx1ZSIp OwogIH0pOwo8L3NjcmlwdD4KPC9ib2R5Pgo8L2h0bWw+Cg== 477770 2025-12-17 11:48:55 -0800 2025-12-17 11:48:55 -0800 Transition using -webkit-box-shadow (broken) test-webkit-box-shadow-transition.html text/html 1410 sam PCFET0NUWVBFIGh0bWw+CjxodG1sPgo8aGVhZD4KPHN0eWxlPgogIC50cmFuc2l0aW9uaW5nIHsK ICAgIHdpZHRoOiA0MDBweDsKICAgIGhlaWdodDogNDAwcHg7CiAgICBiYWNrZ3JvdW5kLWNvbG9y OiByZWQ7CiAgICB0cmFuc2l0aW9uOiBhbGwgMnM7CiAgfQo8L3N0eWxlPgo8L2hlYWQ+Cjxib2R5 Pgo8ZGl2IGlkPSJ0YXJnZXQiIGNsYXNzPSJ0cmFuc2l0aW9uaW5nIj48L2Rpdj4KPHByZSBpZD0i bG9nIj48L3ByZT4KPHNjcmlwdD4KICBmdW5jdGlvbiBsb2cobXNnKSB7CiAgICBkb2N1bWVudC5n ZXRFbGVtZW50QnlJZCgnbG9nJykuYXBwZW5kKG5ldyBUZXh0KG1zZyArICJcbiIpKTsKICB9Cgog IGZ1bmN0aW9uIHRlc3RfcHJvcGVydHkocHJvcGVydHksIHN0YXJ0LCBlbmQpIHsKICAgIHRyeSB7 CiAgICAgIGxvZyhgU1RBUlQ6IFRlc3RpbmcgJHtwcm9wZXJ0eX1gKTsKCiAgICAgIHZhciBkaXYg PSBkb2N1bWVudC5nZXRFbGVtZW50QnlJZCgidGFyZ2V0Iik7CiAgICAgIGRvY3VtZW50LmJvZHku YXBwZW5kQ2hpbGQoZGl2KTsKCiAgICAgIGRpdi5zdHlsZSA9IGAke3Byb3BlcnR5fTogJHtzdGFy dH1gOwogIAogICAgICBnZXRDb21wdXRlZFN0eWxlKGRpdikubWFyZ2luTGVmdDsKCiAgICAgIGRp di5zdHlsZSA9IGAke3Byb3BlcnR5fTogJHtlbmR9YDsKCiAgICAgIGxvZygiQ0hFQ0tJTkcgRk9S IGVsZW1lbnQuZ2V0QW5pbWF0aW9ucygpIikKICAgICAgaWYgKGRpdi5nZXRBbmltYXRpb25zKCku bGVuZ3RoID09IDApCiAgICAgICAgbG9nKCJOTyBBTklNQVRJT05TIEZPVU5EIik7CiAgICAgIGVs c2UKICAgICAgICBsb2coYCR7ZGl2LmdldEFuaW1hdGlvbnMoKS5sZW5ndGh9IEFOSU1BVElPTlMg Rk9VTkQ6ICR7ZGl2LmdldEFuaW1hdGlvbnMoKX1gKTsKCiAgICAgIGRpdi5hZGRFdmVudExpc3Rl bmVyKCd0cmFuc2l0aW9uc3RhcnQnLCBmdW5jdGlvbihldmVudCkgewogICAgICAgIGxvZygidHJh bnNpdGlvbnN0YXJ0IGZpcmVkOiAiICsgZXZlbnQpOwogICAgICB9KTsKCiAgICAgIGRpdi5hZGRF dmVudExpc3RlbmVyKCd0cmFuc2l0aW9ucnVuJywgZnVuY3Rpb24oZXZlbnQpIHsKICAgICAgICBs b2coInRyYW5zaXRpb25ydW4gZmlyZWQ6ICIgKyBldmVudCk7CiAgICAgIH0pOwoKICAgICAgbG9n KGBgKQoKICAgIH0gY2F0Y2ggKGV4Y2VwdGlvbikgewogICAgICBsb2coYEVYQ0VQVElPTjogJHtw cm9wZXJ0eX0gLS0gJHtleGNlcHRpb259XG5gKTsKICAgIH0KICB9CgogIHdpbmRvdy5hZGRFdmVu dExpc3RlbmVyKCJsb2FkIiwgZnVuY3Rpb24oZXZlbnQpIHsKICAgIHRlc3RfcHJvcGVydHkoIi13 ZWJraXQtYm94LXNoYWRvdyIsICIwIDAgMCByZ2JhKDAsIDAsIDAsIDApIiwgIjEwcHggNXB4IDVw eCBibHVlIik7CiAgfSk7Cjwvc2NyaXB0Pgo8L2JvZHk+CjwvaHRtbD4K