Many applications will be able to just substitute the new class names
for the old ones. Apps with golden image tests or with buttons whose
appearance has been configured with constructor parameters or with the
original ButtonTheme may need to consult the migration guide and the
introductory material that follows.

API Change: ButtonStyle instead of individual style properties

A button’s ButtonStyle doesn’t define the button’s visual properties,
it defines overrides of the buttons default visual properties,
where the default properties are computed by the button widget
itself. For example, to override a TextButton’s default foreground
(text/icon) color for all states, one could write:

TextButton

style:

ButtonStyle

foregroundColor:

MaterialStateProperty

all

Color

>(

Colors

blue

),

),

onPressed:

()