void main() -> runApp() -> MaterialApp() -> home: Screen(). For statefulWidget class, we need to add createState function in class and setState({}) when button pressed.

class DiceRoller extends StatefulWidget {
State createState(){ return _DiceRollWidget(); };
}\

class _DiceRollWidget extends State {

void rollDice() {
setState((){...});
}

...
}