[css-forms-1] Define base appearance details element? #11979
Description
In at least chromium currently if you set details to an appearance value other than none (e.g. auto or base-select), the details element's marker is removed. I'm not sure if this is expected or a bug? If it's somewhat expected then we should probably define a base details, even if it's identical to the existing specced styles, so that people doing * { appearance: base; } in future don't end up with unexpected loss of styles on details.
cc @dbaron