(FIXED) As of version 14.0 of Safari on macOS, and release 114 of Safari Technology Preview, Webkit cannot transition the flex-basis property on its own — it has to be included alongside other properties in the transition shorthand.
Update 2020-10-21
Fixed
/* this does not work in Webkit! */
transition: flex-basis 0.3s ease;This works fine in Chromium and Mozilla-based browsers.
To get this working in Webkit, you’ll currently have to use the all value.
/* this works in Webkit */
transition: all 0.3s ease;However, this can be potentially performance heavy, as all properties are being transitioned.