doneit-web/src/app/services/alert.service.ts

import { Injectable } from '@angular/core';
import { AlertController } from '@ionic/angular';

@Injectable({
  providedIn: 'root'
})
export class AlertService {

  constructor(public alertController: AlertController) { }

  async presentAlert(message:string) {
    const alert = await this.alertController.create({
      cssClass: 'my-custom-class',
      header: 'Mensagem do sistema',
      message: message,
      buttons: ['OK']
    });

    await alert.present();
  }

}