how to print warning message in ionic 4 code example

Example: ion alert checkbox

async presentAlertCheckbox() {
    const alert = await this.alertController.create({
      cssClass: 'my-custom-class',
      header: 'Checkbox',
      inputs: [
        {
          name: 'checkbox1',
          type: 'checkbox',
          label: 'Checkbox 1',
          value: 'value1',
          checked: true
        },
        {
          name: 'checkbox2',
          type: 'checkbox',
          label: 'Checkbox 2',
          value: 'value2'
        },
        {
          name: 'checkbox3',
          type: 'checkbox',
          label: 'Checkbox 3',
          value: 'value3'
        }
      ],
      buttons: [
        {
          text: 'Cancel',
          role: 'cancel',
          cssClass: 'secondary',
          handler: () => {
            console.log('Confirm Cancel');
          }
        }, {
          text: 'Ok',
          handler: () => {
            console.log('Confirm Ok');
          }
        }
      ]
    });
    await alert.present();
  }
}