The current proposed change to use mw-ui-button for save/preview/show changes/cancel (on the edit screen) uses mw-ui-destructive (with quiet) for the cancel button.  This directly contradicts the style guide, which says, "This should not be used for cancel buttons.".

As noted at https://gerrit.wikimedia.org/r/#/c/116725/ , my understanding of destructive is that you are deleting something that was already publicly visible, or at least has an impact beyond your own personal session.

The cancel button doesn't seem to fit that.  Cancel is a common concept, and semantically clear, so perhaps we should simply add mw-ui-cancel.