[css-ui] Unprefix 'appearance' and/or make the spec web-compatible #3024
Description
In whatwg/html#3912 there is a proposal to specify two new values of the 'appearance' for the fieldset and legend elements.
I note that none of WebKit, Chromium, Gecko or Edge support 'appearance' unprefixed, but they do support 'webkit-appearance'.
http://software.hixie.ch/utilities/js/live-dom-viewer/saved/6114
Would it be reasonable to unprefix it?
cc @mstensho @MatsPalmgren @dholbert @emilio @thejohnjansen @smfr