How to customize spinner

MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Spinner spinner = findViewById(R.id.spinner);
        ArrayAdapter<String> adapter = new ArrayAdapter<>(
                this,
                R.layout.custom_spinner,
                getResources().getStringArray(R.array.fruit_list)
        );
        adapter.setDropDownViewResource(R.layout.custom_spinner_dropdown);
        spinner.setAdapter(adapter);
    }
}