Top layer

The top layer is a specific layer that spans the
entire width and height of the viewport and sits
on top of all other layers displayed in a web
document. It is created by the browser to contain
elements that should appear on top of all other
content on the page.

Elements that will appear in the top layer
include:

• Fullscreen elements, i.e. elements that have been caused to display in fullscreen mode by a successful Element.requestFullscreen() call.
• elements displayed as a modal via a successful HTMLDialogElement.showModal() call.
• Popover elements shown via a successful HTMLElement.showPopover() call.

Note that the top layer is an internal browser
concept and cannot be directly manipulated from
code.