how to customize dialog box

mport android.os.Bundle;
import android.provider.Settings;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.app.Dialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.content.Intent;
import android.view.Menu;
import android.view.View;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
   
        public void dialog(View v)
        {
Dialog d=new Dialog (MainActivity.this);
 d.setContentView(R.layout.activity_main);
 d.setTitle("internet not working");
 d.show();
        }
}