Re: [css-pseudo] Need a way to styling the disclosure triangle of the <details> (or <summary>) element

I am not much involved with Firefox development anymore, and I don't
know the extent to which this is still true.  But, five years ago when
I *was* deeply involved, it was a basic design goal of the layout
engine that *all* of the semantics of *all* HTML elements should be
defined by their style -- or to put it another way, it should be
possible to turn a <div> into an exact behavioral duplicate of any
other HTML element by applying the correct set of style properties.

This design goal has never been (AFAIK) fully achieved, and to the
extent that it *was* achieved it often involved nonstandard and
undocumented style properties.  But it was a goal, and I expect that
it is the underlying rationale for Firefox's current behavior.

zw