JAVASCRIPT

ionic 3 alert

import { AlertController } from 'ionic-angular';
...
constructor(private alertCtrl: AlertController) {}
...
presentAlert() {
  let alert = this.alertCtrl.create({
    title: 'Low battery',
    subTitle: '10% of battery remaining',
    buttons: ['Dismiss']
  });
  alert.present();
}

ionic 3 alert css custom

let alert = this.alertCtrl.create({
	title: 'Low battery',
    subTitle: '10% of battery remaining',
    buttons: ['Dismiss'],
    cssClass: 'custom-class'
});
alert.present();