If the font size is set in `em` and the font size within the keyframes of an animation are set in `em` then the values will compound instead of interpolating.
Here is an example: https://codepen.io/scottkellum/pen/7c4e82c2744e9dfc0caf706bc525d83f
Behavior in Safari 12 (iOS and Desktop): the text grows and shrinks.
Expected behavior: the animation is between 2em and 2em so it should do nothing. No change in size should occur.
Note on importance: This is a blocker/critical for me because I’m building a fluid typesetting system on top of animations and users want to set text in ems, preventing easy integrations into some websites.
Possibly related bug: https://bugs.webkit.org/show_bug.cgi?id=194765
Different bug. This one reproduces without Web Animations enabled. We're not resolving 'em' styles correctly in animation keyframes.
This has already caused a lot of frustration on my end. Typo centered layout design is dependent on this to work correctly :(