Flutter, how to create border with text embedded?

Does anyone know how to create a border with text at the top like the following where is says "Create an account?

Stack(
  children: <Widget>[
    Container(
      width: double.infinity,
      height: 200,
      margin: EdgeInsets.fromLTRB(20, 20, 20, 10),
      padding: EdgeInsets.only(bottom: 10),
      decoration: BoxDecoration(
        border: Border.all(
            color: Color.fromARGB(255, 51, 204, 255), width: 1),
        borderRadius: BorderRadius.circular(5),
        shape: BoxShape.rectangle,
      ),
    ),
    Positioned(
      left: 50,
      top: 12,
      child: Container(
        padding: EdgeInsets.only(bottom: 10, left: 10, right: 10),
        color: Colors.white,
        child: Text(
          'Create an account',
          style: TextStyle(color: Colors.black, fontSize: 12),
        ),
      ),
    ),
  ],
)