surface property
Opaque fill for raised surfaces and modal content — a Container.filled
widget, or content shown via NavigatorState.present. Unlike background
(nullable = the terminal's own, i.e. effectively transparent), a surface
must fully cover the cells it occupies so nothing painted beneath shows
through. null derives a concrete fill from the theme brightness
(near-black on dark terminals, near-white on light).
Implementation
final Color? surface;