The order property of css-flexbox must be animatable https://drafts.csswg.org/css-flexbox/#order-property Here its a simple test case: https://codepen.io/cl0p3z/pen/YzXMXRB Works on Chrome and Firefox. Fails on WebKit. This its tested by WPT css/css-flexbox/animation/order-interpolation.html
Created attachment 411745 [details] Patch
Created attachment 411844 [details] Patch
r=me assuming EWS results are all green.
Committed r268726: <https://trac.webkit.org/changeset/268726>
<rdar://problem/70481438>