how to make a simple box in dart code example

Example 1: container decoration box flutter

new Container(
  margin: const EdgeInsets.all(15.0),
  padding: const EdgeInsets.all(3.0),
  decoration: BoxDecoration(
    border: Border.all(color: Colors.blueAccent)
  ),
  child: Text("My Awesome Border"),
)

Example 2: box decoration s flutter

Center(  child: new Container(    decoration: new BoxDecoration(      color: Colors.purple,      gradient: new LinearGradient(        colors: [Colors.red, Colors.cyan],        begin: Alignment.centerRight,        end: Alignment.centerLeft      ),    ),    child: new FlutterLogo(      size: 200.0,    )  ),);