Card

A raised surface, and a rule that is only announced when it separates something.

`Card` is deliberately plain: a raised background, a border and a radius, all
from tokens. Not everything is a card — border, fill, radius and shadow each
say "separate object", and stamping the same one on every block flattens the
hierarchy rather than creating it.

`Separator` is `role="none"` without a label and `role="separator"` with one.
A rule that is only decoration should not be announced; one that divides two
meaningful regions should, and then it needs a name.