:root {
  --z-index-base: 0; /** Base stacking level (0) — default in-flow content. */
  --z-index-dropdown: 1000; /** Dropdown menus and select popups. */
  --z-index-sticky: 1100; /** Sticky elements that pin on scroll (headers, toolbars). */
  --z-index-overlay: 1200; /** Full-screen overlay scrims sitting behind modal content. */
  --z-index-modal: 1300; /** Modal dialogs and side sheets. */
  --z-index-popover: 1400; /** Popovers anchored to a trigger, above modals. */
  --z-index-toast: 1500; /** Toast and snackbar notifications. */
  --z-index-tooltip: 1600; /** Tooltips — the top-most interactive layer. */
}