Creating an app theme

To share a Theme across an entire app, provide a
ThemeData to the MaterialApp constructor.

If no theme is provided, Flutter creates a default theme for you.

See the ThemeData documentation to see all of
the colors and fonts you can define.

Themes for part of an application

To override the app-wide theme in part of an application,
wrap a section of the app in a Theme widget.

There are two ways to approach this: creating a unique ThemeData,
or extending the parent theme.

Note:
  To learn more, watch this short Widget of the Week video on the Theme widget:

Creating unique ThemeData

If you don’t want to inherit any application colors or font styles,
create a ThemeData() instance and pass that to the Theme widget.

Extending the parent theme