Obsolete
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
-webkit-transition is a non-standard media feature whose value is a Boolean which is true if the browsing context supports CSS transitions. -webkit-transition was never supported in browsers not based on WebKit or Blink. You should not use this media feature; it was never specified, has never been widely implemented, and has been removed from all browsers.
Use @supports instead
If you need to determine whether or not CSS transitions are supported in your stylesheet, you should avoid using -webkit-transition. Instead, test for transition support using the CSS at-rule @supports, like this:
@supports(transition: initial) {
/* CSS to use if transitions are supported */
}
Example
Before this become obsolete, you could use -webkit-transition in your CSS like this:
@media(-webkit-transition) {
/* CSS to use if transitions are supported */
}
However, this media query no longer works and should be replaced with the code shown above in Use supports instead above.
Specifications
Not part of any specification. Apple has a description in Safari CSS Reference; this is now called simply transition there.