:root{
  /* Depth is carried by the surface ladder and hairlines; shadow is a last resort. */
  --elev-0:none;
  --elev-1:none;                                   /* surface-1 + hairline */
  --elev-2:0 1px 0 0 var(--hairline-bright) inset; /* top edge highlight on lifted panels */
  --elev-3:0 8px 24px -12px rgba(0,0,0,.65);       /* dropdowns, popovers */
  --elev-4:0 24px 64px -24px rgba(0,0,0,.8);       /* dialogs only */
  --edge-top:inset 0 1px 0 0 var(--hairline-bright);
}