text_rich.dart

class _MyHomePageState extends State<MyHomePage> {
  String playerName = "Serena";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Text.rich(
          TextSpan(text: "It is ", children: <TextSpan>[
            TextSpan(
                text: "$playerName's ",
                style: TextStyle(
                  color: Colors.redAccent, // <- override the color
                  fontSize: 100, // <- override the font size
                  fontWeight: FontWeight.bold,  // <- override the font weight
                )),
            TextSpan(text: "turn to serve.")
          ]),
          style: TextStyle(
              fontWeight: FontWeight.w100,
              fontSize: 30,
              fontFamily: 'Roboto',
              color: Colors.white),
        ),
      ),
    );
  }
}