Limit max width of Container in Flutter

You can add a constraint to the Container Widget with the preferred maxWidth like this:

Widget build(context) {
return Row(
  mainAxisSize: MainAxisSize.min,
  children: [
    Container(
      constraints: BoxConstraints(minWidth: 100, maxWidth: 200),
      padding: EdgeInsets.all(10),
      decoration: BoxDecoration(
        color: color ?? Colors.blue,
        borderRadius: BorderRadius.circular(10)
      ),
      child: msg
    )
  ],  
);
}