anchor.diff:        // and the op keypad have sizes proportional to their number of
         // columns.
         flex: 3,
  -      child: new Material(
  -        elevation: 12,
  -        color: Colors.grey[800],
  -        child: new Column(
  -          children: <Widget>[
  -            new KeyRow(<Widget>[
  -              new NumberKey(7, calcState),
  -              new NumberKey(8, calcState),
  -              new NumberKey(9, calcState)
  -            ]),
  -            new KeyRow(<Widget>[
  -              new NumberKey(4, calcState),
  -              new NumberKey(5, calcState),
  -              new NumberKey(6, calcState)
  -            ]),
  -            new KeyRow(<Widget>[
  -              new NumberKey(1, calcState),
  -              new NumberKey(2, calcState),
  -              new NumberKey(3, calcState)
  -            ]),
  -            new KeyRow(<Widget>[
  -              new CalcKey('.', calcState.handlePointTap),
  -              new NumberKey(0, calcState),
  -              new CalcKey('=', calcState.handleEqualsTap),
  -            ])
  -          ]
  -        )
  +      child: new Column(
  +        children: <Widget>[
  +          new KeyRow(<Widget>[
  +            new NumberKey(7, calcState),
  +            new NumberKey(8, calcState),
  +            new NumberKey(9, calcState)
  +          ]),
  +          new KeyRow(<Widget>[
  +            new NumberKey(4, calcState),
  +            new NumberKey(5, calcState),
  +            new NumberKey(6, calcState)
  +          ]),
  +          new KeyRow(<Widget>[
  +            new NumberKey(1, calcState),
  +            new NumberKey(2, calcState),
  +            new NumberKey(3, calcState)
  +          ]),
  +          new KeyRow(<Widget>[
  +            new CalcKey('.', calcState.handlePointTap),
  +            new NumberKey(0, calcState),
  +            new CalcKey('=', calcState.handleEqualsTap),
  +          ])
  +        ]
         )
       );
     }
  
positive.code: 
    @override
    Widget build(BuildContext context) {
      return new Flexible(
        flex: _flex,
        child: new Row(
          children: <Widget>[
            new MainKeyPad(calcState: calcState),
            new OpKeyPad(calcState: calcState),
          ]
        )
      );
    }
  
negative.code: 
    @override
    Widget build(BuildContext context) {
      final ThemeData themeData = Theme.of(context);
      return new Flexible(
        child: new Material(
          color: themeData.backgroundColor,
          child: new Column(
            children: <Widget>[
              new CalcKey('\u232B', calcState.handleDelTap),
  