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Code Explained - The About Page :

​import 'package:flutter/material.dart';

class AnswerButton extends StatelessWidget {

  final String _answer;
  final VoidCallback _onTap;

  AnswerButton(this._answer, this._onTap);

  @override
  Widget build(BuildContext context) {
    return new Expanded( // true button
      child: new Material(
        color: _answer == "A"? Colors.green : _answer == "B" ? Colors.redAccent: _answer == "C" ? Colors.blueAccent: Colors.deepOrangeAccent,
        child: new InkWell(
          onTap: () => _onTap(),
          child: new Center(
              child: new Container(
                decoration: new BoxDecoration(
                   // border: new Border.all(color: Colors.white, width: 1.0)
                ),

                padding: new EdgeInsets.all(10.0),
                child: new Text(_answer == "A" ? "A" : _answer == "B" ? "B": _answer == "C" ? "C": "D",
                    style: new TextStyle(color: Colors.white, fontSize: 40.0, fontWeight: FontWeight.bold, fontStyle: FontStyle.italic)
                ),
              )
          ),
        ),
      ),
    );
  }
}

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