How to custom appbar style inside SearchDelegate

Question

I created a search function with new class extends SearchDelegate. And I want to custom appBar background color, font size. How to achieve this?

My search class

import 'package:flutter/material.dart';

class Search extends SearchDelegate {
  final List countryList;

  Search(this.countryList);

  @override
  List<Widget> buildActions(BuildContext context) {
    return [
      IconButton(
        icon: Icon(Icons.clear),
        onPressed: () {
          query = '';
        },
      )
    ];
  }

  @override
  Widget buildLeading(BuildContext context) {
    return IconButton(
      icon: Icon(Icons.arrow_back_ios),
      onPressed: () {
        Navigator.pop(context);
      },
    );
  }

  @override
  Widget buildResults(BuildContext context) {
    return Container();
  }

  @override
  Widget buildSuggestions(BuildContext context) {
    final suggestionList = query.isEmpty
        ? countryList
        : countryList
            .where((element) =>
                element['country'].toString().toLowerCase().startsWith(query))
            .toList();

    return ListView.builder(
      itemCount: suggestionList.length,
      itemBuilder: (context, index) {
        return Card(
          child: Container(
            height: 70,
            margin: EdgeInsets.symmetric(horizontal: 10, vertical: 10),
            child: Row(
              children: <Widget>[
                Container(
                  width: 200,
                  margin: EdgeInsets.symmetric(horizontal: 10),
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.start,
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Text(
                        suggestionList[index]['country'],
                        style: TextStyle(fontWeight: FontWeight.bold),
                      ),
                      Image.network(
                        suggestionList[index]['countryInfo']['flag'],
                        height: 50,
                        width: 60,
                      ),
                    ],
                  ),
                ),
                Expanded(
                    child: Container(
                  child: Column(
                    children: <Widget>[
                      Text(
                        'CONFIRMED:' +
                            suggestionList[index]['cases'].toString(),
                        style: TextStyle(
                          fontWeight: FontWeight.bold,
                          color: Colors.red,
                        ),
                      ),
                      Text(
                        'ACTIVE:' + suggestionList[index]['active'].toString(),
                        style: TextStyle(
                          fontWeight: FontWeight.bold,
                          color: Colors.blue,
                        ),
                      ),
                      Text(
                        'RECOVERED:' +
                            suggestionList[index]['recovered'].toString(),
                        style: TextStyle(
                          fontWeight: FontWeight.bold,
                          color: Colors.green,
                        ),
                      ),
                      Text(
                        'DEATHS:' + suggestionList[index]['deaths'].toString(),
                        style: TextStyle(
                          fontWeight: FontWeight.bold,
                          color: Theme.of(context).brightness == Brightness.dark
                              ? Colors.grey[100]
                              : Colors.grey[900],
                        ),
                      ),
                    ],
                  ),
                ))
              ],
            ),
          ),
        );
      },
    );
  }
}

This class create a appbar like this

When I try to change backgound color use

ThemeData appBarTheme(BuildContext context) {
  return ThemeData(
    primaryColor: Color(0xff202c3b),
  );
}

Background color changed but some style are changed too

I want to custom a little bit style like

• Font size bigger
• Font color to white
• Don't use underline

How to achieve this? I can't find any TextStyle or something like that

EDITED

CountryPage class for use search

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

import 'package:tgd_covid_tracker/pages/search.dart';

class CountryPage extends StatefulWidget {
  @override
  _CountryPageState createState() => _CountryPageState();
}

class _CountryPageState extends State<CountryPage> {
  List countryData;

  fetchCountryData() async {
    if (this.mounted) {
      http.Response response =
          await http.get('https://corona.lmao.ninja/v2/countries');
      setState(() {
        countryData = json.decode(response.body);
      });
    }
  }

  @override
  void initState() {
    fetchCountryData();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        actions: <Widget>[
          countryData == null
              ? Container()
              : searchButton(
                  context,
                  countryData,
                ),
        ],
        title: Text('Country Stats'),
      ),
      body: countryData == null
          ? Center(
              child: CircularProgressIndicator(),
            )
          : ListView.builder(
              itemBuilder: (context, index) {
                return Card(
                  child: Container(
                    height: 70,
                    margin: EdgeInsets.symmetric(horizontal: 10, vertical: 10),
                    child: Row(
                      children: <Widget>[
                        Container(
                          width: 200,
                          margin: EdgeInsets.symmetric(horizontal: 10),
                          child: Column(
                            crossAxisAlignment: CrossAxisAlignment.start,
                            mainAxisAlignment: MainAxisAlignment.center,
                            children: <Widget>[
                              Text(
                                countryData[index]['country'],
                                style: TextStyle(fontWeight: FontWeight.bold),
                              ),
                              Image.network(
                                countryData[index]['countryInfo']['flag'],
                                height: 50,
                                width: 60,
                              ),
                            ],
                          ),
                        ),
                        Expanded(
                          child: Container(
                            child: Column(
                              children: <Widget>[
                                Text(
                                  'CONFIRMED:' +
                                      countryData[index]['cases'].toString(),
                                  style: TextStyle(
                                    fontWeight: FontWeight.bold,
                                    color: Colors.red,
                                  ),
                                ),
                                Text(
                                  'ACTIVE:' +
                                      countryData[index]['active'].toString(),
                                  style: TextStyle(
                                    fontWeight: FontWeight.bold,
                                    color: Colors.blue,
                                  ),
                                ),
                                Text(
                                  'RECOVERED:' +
                                      countryData[index]['recovered']
                                          .toString(),
                                  style: TextStyle(
                                    fontWeight: FontWeight.bold,
                                    color: Colors.green,
                                  ),
                                ),
                                Text(
                                  'DEATHS:' +
                                      countryData[index]['deaths'].toString(),
                                  style: TextStyle(
                                    fontWeight: FontWeight.bold,
                                    color: Theme.of(context).brightness ==
                                            Brightness.dark
                                        ? Colors.grey[100]
                                        : Colors.grey[900],
                                  ),
                                ),
                              ],
                            ),
                          ),
                        )
                      ],
                    ),
                  ),
                );
              },
              itemCount: countryData == null ? 0 : countryData.length,
            ),
    );
  }
}

Widget searchButton(BuildContext context, countryData) {
  return IconButton(
    icon: Icon(Icons.search),
    onPressed: () {
      showSearch(context: context, delegate: Search(countryData));
    },
  );
}

Answer 1

The following works flawlessly:

class CustomSearchDelegate extends SearchDelegate {
  @override
  ThemeData appBarTheme(BuildContext context) {
    return ThemeData(
      textTheme: TextTheme(
        // Use this to change the query's text style
        headline6: TextStyle(fontSize: 24.0, color: Colors.white),
      ),
      appBarTheme: const AppBarTheme(
        backgroundColor: Colors.green,
      ),
      inputDecorationTheme: InputDecorationTheme(
        border: InputBorder.none,
        
        // Use this change the placeholder's text style
        hintStyle: TextStyle(fontSize: 24.0),
      ),
    );
  }
}