Fullscreen mode in the shadow DOM

The editor is built in the root picked below. In the shadow modes the editor stylesheets are forwarded into that root and disabled in the main document, so the fullscreen layer is styled only if it lands in a root that adopted them – which is exactly what this test watches.

Where the layer is expected to mount, by combination:

• With Overlay layer in its own container on (the default), the layer mounts in that separate container – not in the editor's own root – because the editor resolves its floating UI against the configured ui.overlayContainer. The editable moves there with it for as long as fullscreen is on.
• With it off, the editor resolves the root it lives in on its own, so the layer mounts in the editor's root (or document.body in the light DOM).
• With Fullscreen in a custom container on, fullscreen.container wins over both. That container lives inside the editor's root and is easy to spot: it inverts its colors.

In every combination the layer must be fully styled, the toolbar and the menu bar must work from inside it, and leaving fullscreen must put the editable back where it came from. A closed root cannot be resolved through host.shadowRoot, so reach it from the console through the editor: editor.editing.view.getDomRoot().getRootNode().