Hello bro try this one!
Container( child: Center(child: Text('Geeks for Geeks')), height: 100, width: 100, decoration: BoxDecoration( borderRadius:BorderRadius.circular(50) , boxShadow: [ BoxShadow( color: Colors.green, ), BoxShadow( color: Colors.white70, spreadRadius: -5.0, blurRadius: 20.0, ), ], ),

Here is the code for your problem. You just have to take a simple container with a border radius in boxdecoration.
new Container( alignment: Alignment.center, decoration: BoxDecoration( borderRadius: BorderRadius.all(Radius.circular(15.0)), color: Colors.blue, ),
child: Row( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Padding( padding: const EdgeInsets.all(10.0), child: new Text( "Next", style: new TextStyle( fontWeight: FontWeight.w500, color: Colors.white, fontSize: 15.0, ), ), ), ], ), ),