Created attachment 357723 [details] animating scrollable content to expose paint order bug Can't seem to find a webkit bug tracking this, though it is seemingly known among vendor developers (https://github.com/w3c/csswg-drafts/issues/2717#issuecomment-395911418) 1. Open the attached case. 2. Watch overflow:auto box that has green content grow and shrink, creating and removing user scrollable content every 2 seconds. 3. See that when it overflows, it behaves as-if-positioned painted higher and lower in order than the red block (which also is always lifted higher because of overflow). Compat Firefox doesn't let "user scrollable" overflow affect paint order, red block is always behind green in test case. Blink has same/similar issue, but is working on fix??? https://bugs.chromium.org/p/chromium/issues/detail?id=370604#c_ts1545253494 *I say user scrollable, because overflow:hidden doesn't create compositing order issue
<rdar://problem/46887177>