Check out example codes for "container flutter border radius". It will help you in understanding the concepts better.

Code Example 1

Container(
	decoration: BoxDecoration(
    	color: Colors.blue,
    	borderRadius: BorderRadius.all(
    		Radius.circular(10)
    	)
    )
)

Code Example 2

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

Code Example 3

Container(
      child: Text(
          'This is a Container',
          textScaleFactor: 2,
          style: TextStyle(color: Colors.black),
      ),

      decoration: BoxDecoration(
          borderRadius: BorderRadius.circular(10),
          color: Colors.white,
          border: Border(
              left: BorderSide(
                  color: Colors.green,
                  width: 3,
              ),
            ),
          ),
      height: 50,
     ),

Code Example 4

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"),
           )
         ),
        ),

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