Marks the page as owned by DataCube, i.e. DataCube is the whole page rather than embedded.
NOTE: popups portaled by shared components (e.g. selector menus) can't carry the theme class,
so the dark theme styles them with page-wide rules, as well as the page background. These rules
only apply to a page marked as owned by DataCube, so they never re-theme the host's own popups.
Marks the page as owned by DataCube, i.e. DataCube is the whole page rather than embedded.
NOTE: popups portaled by shared components (e.g. selector menus) can't carry the theme class, so the dark theme styles them with page-wide rules, as well as the page background. These rules only apply to a page marked as owned by DataCube, so they never re-theme the host's own popups.