https://drafts.csswg.org/css-ui-4/#appearance-switching

Value: auto | none

For this testcase, the output in the Console in Chrome, Safari and Edge is:

div: none
select with -webkit-appearance:inherit: none
button: button
button w. -webkit-appearance:initial: none

I think that makes it clear that the initial value for -webkit-appearance is none in those UAs. I believe the initial value for appearance must be the same.

After implementing appearance according to spec in Gecko (with auto as the initial value and -webkit-appearance as an alias) we found that this isn't web-compatible.

We will now try with none as the initial value instead, and override that with appearance:auto in the UA sheet for elements that have a native theme in Gecko, <button> <select> etc.