How to customize spinner

MainActivity.kt

class MainActivity : AppCompatActivity(){
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val spinner = findViewById<Spinner>(R.id.spinner)
        val adapter = ArrayAdapter(
            this,
            R.layout.custom_spinner,
            resources.getStringArray(R.array.fruit_list)
        )
        adapter.setDropDownViewResource(R.layout.custom_spinner_dropdown)
        spinner.adapter = adapter
    }
}