new Container(
          height: 300.0,
          color: Colors.transparent,
          child: new Container(
            decoration: new BoxDecoration(
              color: Colors.green,
              borderRadius: new BorderRadius.only(
                topLeft: const Radius.circular(40.0),
                topRight: const Radius.circular(40.0),
              )
            ),
            child: new Center(
            child: new Text("Hi modal sheet"),
           )
         ),
        ),

Container(
  child: Text("It's text..."),
  decoration: BoxDecoration(
    borderRadius: BorderRadius.circular(10),  // radius of 10
    color: Colors.green  // green as background color
  )
)

borderRadius: BorderRadius.only(
          topRight: Radius.circular(10.0),
          bottomRight: Radius.circular(10.0)),

Container(
  decoration: BoxDecoration(
    border: Border.all(
      color: Colors.red[500],
    ),
    borderRadius: BorderRadius.all(Radius.circular(20))
  ),
  child: ...
)

Container(
  child: Text(
    'This is a Container',
    textScaleFactor: 2,
    style: TextStyle(color: Colors.black),
  ),
  decoration: BoxDecoration(
    borderRadius: BorderRadius.circular(10),
    color: Colors.white,
    boxShadow: [
      BoxShadow(color: Colors.green, spreadRadius: 3),
    ],
  ),
  height: 50,
),

Container(
   decoration: BoxDecoration(
   borderRadius: BorderRadius.circular(20.0),
   color: Colors.red,
   ),
   child: 
),