:root {
  /* Depth = lighter surface + hairline; shadow reserved for overlays + active glow */
  --elev-0: none;
  --elev-1: 0 0 0 1px var(--hairline);
  --elev-2: 0 6px 16px -6px rgba(0,0,0,.6);          /* popover, menu */
  --elev-3: 0 18px 44px -12px rgba(0,0,0,.75);       /* sheet, modal, FAB */
  --glow: 0 10px 28px -8px rgba(255,164,21,.6);      /* active / on */
}