Radius and elevation are fused into one named tier so a component picks a single value that carries both — 3 tiers total, because Scrums' radius never varies and elevation is shadow-free.

• One property, not two — a component declares material="elevated", never sets border and accent-edge separately
• No stacking — two Materials never nest on the same element; extra lift is delegated to a new element
• Decorative, not semantic — role="dialog" is still set independently; Material carries zero ARIA meaning
• Lowest-tier-that-works wins — reach for material-surface before material-elevated