Flutter design

Stack(
  alignment: Alignment.center,
  textDirection: TextDirection.rtl,
  fit: StackFit.loose,
  overflow: Overflow.visible,
  clipBehavior: Clip.hardEdge,
  children: <Widget>[]
),

gradient

gradient: LinearGradient(
              begin: Alignment.topRight,
              end: Alignment.bottomLeft,
              colors: [
                Colors.blue,
                Colors.red,
              ],
            )

Tabbar

DefaultTabController(
  length: 3,
  child: Scaffold(
    appBar: AppBar(
      bottom: TabBar(
        tabs: [
          Tab(icon: Icon(Icons.flight)),
          Tab(icon: Icon(Icons.directions_transit)),
          Tab(icon: Icon(Icons.directions_car)),
        ],
      ),
      title: Text('Tabs Demo'),
    ),
    body: TabBarView(
      children: [
        Icon(Icons.flight, size: 350),
        Icon(Icons.directions_transit, size: 350),
        Icon(Icons.directions_car, size: 350),
      ],
    ),
  ),
);

alert box

showAlertDialog(BuildContext context,{topic,description,onCancel,onContinue}) {
  // set up the buttons
  Widget cancelButton = TextButton(
    child: Text("Cancel"),
    onPressed:  onCancel,
  );
  Widget continueButton = TextButton(
    child: Text("Continue"),
    onPressed:  onContinue,
  );
  // set up the AlertDialog
  AlertDialog alert = AlertDialog(
    title: Text(topic),
    content: Text(description),
    actions: [
      cancelButton,
      continueButton,
    ],
  );
  // show the dialog
  showDialog(
    context: context,
    builder: (BuildContext context) {
      return alert;
    },
  );
}