text: // Z-index values
  const base = 0;
  const above = 1; // use this for all values above the base
  const below = -1; // and this for all values below the base
  
  // Page Layout
  const zLayoutNavigation = above + base;
  const zLayoutFooter = above + base;
  const zLayoutModal = above + zLayoutNavigation;
  const zLayoutPopUpAd = above + zLayoutModal;
  
  // NavMenu
  const zNavMenuBackdrop = below + base;
  const zNavMenuPopover = above + base;
  const zNavMenuToggle = above + zNavMenuPopover;
  
  // Usage ---
  
  // Your usage will depend on what you're using for styling.
  // Here is a plain JSX style example
  
  const Nav = () => <nav style={{ zIndex: zLayoutNavigation }} />;
  