Add a glass to ion-page

Thanks @Splinter1997. But my issue is how to apply over the very parent class, like ion-app or ion-page, which are not editable in the HTML file. I can set the above [ngClass] to a ion-header, ion-content, but that does not do the job for me, because I have alot of subclasses for the header , toolbar, which i want to parrent out to one global class applied over the ion-app or ion-page.
I guess I will still need to use document.querySelector