Standard buttons now capitalize each word in their labels. Movement and
depth-shadow changes use an 80ms duration while color transitions stay
at 120ms.
Neutral buttons in dark mode now use a white 8% depth edge so it matches
the regular border. Highlighted buttons keep the accent-mixed edge.
Document the behavior and assert the dark-mode selector in CSS tests.
Standard .button controls now use a compact 2px bottom edge, lift 1px on
hover, and press down with the depth removed. Highlighted buttons mix the
accent with black for a matching edge, and focus-visible keeps the accent
ring. Other button-like controls still use the lighter scale press.