You can add the Text as a child to a Container that has a BoxDecoration with border property:

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'),)

Here is an expanded answer. A DecoratedBox is what you need to add a border, but I am using a Container for the convenience of adding margin and padding.

Here is the general setup.

Widget myWidget() {  return Container(    margin: const EdgeInsets.all(30.0),    padding: const EdgeInsets.all(10.0),    decoration: myBoxDecoration(), //             <--- BoxDecoration here    child: Text(      "text",      style: TextStyle(fontSize: 30.0),    ),  );}

where the BoxDecoration is

BoxDecoration myBoxDecoration() {  return BoxDecoration(    border: Border.all(),  );}

Border width

These have a border width of 1, 3, and 10 respectively.

BoxDecoration myBoxDecoration() {  return BoxDecoration(    border: Border.all(      width: 1, //                   <--- border width here    ),  );}

Border color

These have a border color of

• Colors.red
• Colors.blue
• Colors.green

Code

BoxDecoration myBoxDecoration() {  return BoxDecoration(    border: Border.all(      color: Colors.red, //                   <--- border color      width: 5.0,    ),  );}

Border side

These have a border side of

• left (3.0), top (3.0)
• bottom (13.0)
• left (blue[100], 15.0), top (blue[300], 10.0), right (blue[500], 5.0), bottom (blue[800], 3.0)

Code

BoxDecoration myBoxDecoration() {  return BoxDecoration(    border: Border(      left: BorderSide( //                   <--- left side        color: Colors.black,        width: 3.0,      ),      top: BorderSide( //                    <--- top side        color: Colors.black,        width: 3.0,      ),    ),  );}

Border radius

These have border radii of 5, 10, and 30 respectively.

BoxDecoration myBoxDecoration() {  return BoxDecoration(    border: Border.all(      width: 3.0    ),    borderRadius: BorderRadius.all(        Radius.circular(5.0) //                 <--- border radius here    ),  );}

Going on

DecoratedBox/BoxDecoration are very flexible. Read Flutter — BoxDecoration Cheat Sheet for many more ideas.

The best way is using BoxDecoration()

Advantage

• You can set the border of a widget
• You can set the border Color or Width
• You can set a Rounded corner of a border
• You can add a Shadow of a widget

Disadvantage

• BoxDecoration only use with Container widget, so you want to wrap your widget in Container()

Example

    Container(      margin: EdgeInsets.all(10),      padding: EdgeInsets.all(10),      alignment: Alignment.center,      decoration: BoxDecoration(        color: Colors.orange,        border: Border.all(            color: Colors.pink[800], // Set border color            width: 3.0),   // Set border width        borderRadius: BorderRadius.all(            Radius.circular(10.0)), // Set rounded corner radius        boxShadow: [BoxShadow(blurRadius: 10,color: Colors.black,offset: Offset(1,3))] // Make rounded corner of border      ),      child: Text("My demo styling"),    )