How to resize spinner buttons of a ion-input type number in a ion-alert?

I would like to resize the spinner buttons of the number input I declared in a ion-alert.

view of the too small spinner buttons

I tried tips I found but it does not work in my case. In my ts file:

const alert = await this.alertController.create({
     header: 'input type=number in an ion-alert',
         inputs: [
             {
                 label: 'MyLabel',
                 type: 'number',
                 value: 6,
                 cssClass: 'myCustomClass',
             },
         ],

In global.scss:

ion-spinner.alert-input.myCustomClass{
     width: 3em;
     height: 3em;
}