Ionic slide scrollbar

I try to add an io-slides to my app but i can’t add vertical scroll.
I tried with the following CSS, without success:

ion-slides {
     height: 100%;
ion-slide.swiper-slide {
   align-items: flex-start;

.swiper-slide {
   overflow-y: scroll !important;
   display: block;

I’m using Ionic 4.

I’m trying the application on the browser but I strangely noticed that if I disable the device vision the scroll bar appears.