I don't see why this shouldn't be possible: ```css #element { animation: size 1s infinite alternate; } @keyframes size { from { inline-size: 100px } to { inline-size: 200px } } ``` I expect it to animate just like if I used `width`. But the [spec](https://drafts.csswg.org/css-logical/#dimension-properties) says > Animation type: discrete On Chrome it's effectively discrete, on Firefox it doesn't animate at all. https://jsfiddle.net/45e6okrm/