when using animation-play-state: paused on an animated element and using a transition on a parent element, Safari, Safari TP and WebKit Nightly are suddenly recalculating styles all the time, causing a high cpu load. Opening the Web Inspector causes an even higher CPU load (using WebKit Nightly):
Try to open the page in Safari and hover over the card. Then open the Web Inspector.
The same is happening in MobileSafari on iOS 11.2(.x), causing the battery to drain fast.
Next, try opening:
There, the issue doesn't happen, as the animation is not paused (also no high cpu usage in the Web Inspector).
Created attachment 340325 [details]
Comment on attachment 340325 [details]
Clearing flags on attachment: 340325
Committed r231794: <https://trac.webkit.org/changeset/231794>
All reviewed patches have been landed. Closing bug.