The brightness of the overall theme of the application. Used by widgets like buttons to determine what color to pick when not using the primary or accent color.
When the Brightness is dark, the canvas, card, and primary colors are all dark. When the Brightness is light, the canvas and card colors are bright, and the primary color's darkness varies as described by primaryColorBrightness. The primaryColor does not contrast well with the card and canvas colors when the brightness is dark; when the brightness is dark, use Colors.white or the accentColor for a contrasting color.
final Brightness brightness