ButtonTheme

OutlinedButton

OutlinedButtonTheme

The new themes follow the “normalized” pattern that Flutter adopted
for new Material widgets about a year ago. Theme properties and widget
constructor parameters are null by default. Non-null theme properties
and widget parameters specify an override of the component’s default
value. Implementing and documenting default values is the sole
responsibility of the button component widgets. The defaults
themselves are based primarily on the overall Theme’s colorScheme and
textTheme.

Visually, the new buttons look a little different, because they match
the current Material Design spec and because their colors are
configured in terms of the overall Theme’s ColorScheme. There are
other small differences in padding, rounded corner radii, and the
hover/focus/pressed feedback.