Change style of element from #shadow-root in CSS sheet (angular/ionic code)

<ion-segment-button _ngcontent-rao-c6="" class="seg-btn md segment-button-has-label segment-button-has-label-only segment-button-layout-icon-top ion-activatable ion-activatable-instant hydrated segment-button-checked" mode="md" style="--indicator-color-checked: #ff3366;--margin:0px 20px;" value="glucose" ng-reflect-mode="md" ng-reflect-value="glucose">
           
          #shadow-root(open)
             <button type="button" class="button-native" aria-pressed="true"><slot></slot><ion-ripple- 
                effect role="presentation" class="ios hydrated"></ion-ripple-effect></button>
             <div class="segment-button-indicator"></div>

   <ion-label _ngcontent-rao-c6="" class="detailsGroupName sc-ion-label-ios-h sc-ion-label-ios-s ios 
   hydrated">
       Glucose
   </ion-label>
      
</ion-segment-button>

I'm trying to style <div class="segment-button-indicator> that is inside the #shadow-root in the css style sheet, with the properties {width:30px, self-align:center}.

What selector must i use to be able to access and style it in the css sheet?