Check out example codes for "raisedbutton full width flutter". It will help you in understanding the concepts better.

Code Example 1

FractionallySizedBox(
   widthFactor: 1, // means 100%, you can change this to 0.8 (80%)
     child: RaisedButton.icon(
     onPressed: () {
     	print(comment);
     },
     label: Text('Edit Comment', style: TextStyle(color: Colors.white)),
     icon: Icon(Icons.check, color: Colors.white),
     ),
 ),

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