CSS Transition of inherited value sequenced across children elements

• Component: Animations
• Status: NEW ---

[Meir Cohen]

Transition of inherited value, such as `text-indent`, in nested elements, is happening in sequence and not simultaneously with the transition of the parent value.

Here is a codepen demonstrates the issue: https://codepen.io/meirkoen/pen/mdVGRYj?editors=1100
On the left side you can see 3 variants of the issue.
On the right side you can see how it can be fixed - by specifying the values on the children as well.

I have tried to search the [css-transitions] https://drafts.csswg.org/css-transitions/ spec for a definition of this behaviour but I did not see one.

I've also opened an issue in csswg-drafts (https://github.com/w3c/csswg-drafts/issues/5324) to make sure that it's not an ambiguity in the spec at this section https://drafts.csswg.org/css-transitions/#starting. 

I also confirmed that it works well in Firefox

[Radar WebKit Bug Importer]

<rdar://problem/65935293>

[Antoine Quint]

Pretty amazing, thanks for filing Meir! There are transition events fired on each frame here.

[Antoine Quint]

This issues reproduces with a Safari build that predates the new Web Animations engine, this is likely a bug in the CSS code that generates the Animation objects fed to Style::TreeResolver::createAnimatedElementUpdate().

[Antoine Quint]

Created attachment 405683 [details]
Reduction

I've reduced the test further to just a color transition on <p> and nested <span> without any text-ident or display styles.

[Antoine Quint]

This test only works correctly in Firefox, both Chrome and Safari have the wrong behavior of staggering the animations across elements.