:root {
    /* region basis rungs — signed depth ladder as box-shadow recipes (NOT z-index) */
    --cem-recess-2: inset 0 2px 4px rgba(0, 0, 0, 0.08), inset 0 1px 2px rgba(0, 0, 0, 0.04);
    --cem-recess-1: inset 0 1px 2px rgba(0, 0, 0, 0.04);
    --cem-elevation-0: none;
    --cem-elevation-1: 0 1px 2px rgba(0, 0, 0, 0.06), 0 1px 1px rgba(0, 0, 0, 0.04);
    --cem-elevation-2: 0 2px 4px rgba(0, 0, 0, 0.08), 0 1px 2px rgba(0, 0, 0, 0.06);
    --cem-elevation-3: 0 4px 8px rgba(0, 0, 0, 0.10), 0 2px 4px rgba(0, 0, 0, 0.08);
    --cem-elevation-4: 0 8px 16px rgba(0, 0, 0, 0.12), 0 4px 8px rgba(0, 0, 0, 0.10);
    
    /* endregion basis rungs */

    /* region semantic endpoints — required product-facing contract */
    --cem-layer-back: var(--cem-recess-1);
    --cem-layer-base: var(--cem-elevation-0);
    --cem-layer-work: var(--cem-elevation-1);
    --cem-layer-overlay: var(--cem-elevation-3);
    --cem-layer-command: var(--cem-elevation-4);
    
    /* endregion semantic endpoints */

    /* region optional semantic endpoints — back-deep / work-floating */
    --cem-layer-back-deep: var(--cem-recess-2);
    --cem-layer-work-floating: var(--cem-elevation-2);
    
    /* endregion optional semantic endpoints */
}

/* region forced-colors fallback — collapse rungs; tier signal carried by D5 contour and spatial isolation */
@media (forced-colors: active) {
    :root {
        --cem-recess-2: none;
        --cem-recess-1: none;
        --cem-elevation-0: none;
        --cem-elevation-1: none;
        --cem-elevation-2: none;
        --cem-elevation-3: none;
        --cem-elevation-4: none;
        
    }
}
/* endregion forced-colors fallback */