brownBox method
Wraps the widget in a ColoredBox with system brown color.
Uses CupertinoColors.systemBrown which adapts to light/dark mode. This is the standard brown color used throughout iOS interfaces, often used for earth-toned or natural-themed elements.
Returns a ColoredBox containing the current widget with brown background.
Example:
Text('Natural').brownBox()
Implementation
ColoredBox brownBox() => coloredBox(CupertinoColors.systemBrown);