System

Layers. An eleven-step stacking order for every overlay.

The Stack

Eleven named layers, ordered by what has to cover what. The registry has no z-index tokens, so this order exists only here. The point of naming them is that z-dropdown above z-header states a relationship, where z-60 above z-50 states a number somebody once picked.

Token	Value	Use
raised	10	A card or tile lifting under the pointer. The floor of the stack: anything that just needs to beat its own siblings.
sticky	20	A sticky element inside the page body, such as a table header or the section rail on this page.
banner	25	A page-level notice sitting above sticky content but below the site chrome.
drawer	30	The Milo drawer.
mobile-menu	40	The mobile navigation panel, which must cover the drawer.
header	50	The site header. Above the page and its own sticky children, below anything it opens.
dropdown	60	A menu or popover opened FROM the header, so it has to clear it.
overlay	70	The scrim behind a modal.
modal	80	The modal itself, one step above its own scrim.
toast	90	A toast, which must be readable over an open modal.
max	999	The escape hatch. Nothing in this codebase should reach for it without a reason written at the call site.