Reland https://github.com/flutter/flutter/pull/141818 with a fix for a special case: If only `background` is specified for `TextButton.styleFrom` or `OutlinedButton.styleFrom` it applies the button's disabled state, i.e. as if the same value had been specified for disabledBackgroundColor.
The change relative to #141818 is the indicated line below:
```dart
final MaterialStateProperty<Color?>? backgroundColorProp = switch ((backgroundColor, disabledBackgroundColor)) {
(null, null) => null,
(_, null) => MaterialStatePropertyAll<Color?>(backgroundColor), // ADDED THIS LINE
(_, _) => _TextButtonDefaultColor(backgroundColor, disabledBackgroundColor),
};
```
This backwards incompatibility cropped up in an internal test, see internal Google issue b/323399158.
c6f2cea65e