Problem with ion-segment-button custom CSS

I want to have a custom background color when my ion-segment-button is selected.
I tried this in my component:

<ion-segment-button class="actsegment" value="10">

and this in my scss:

ion-segment-button.actsegment {
    --color-checked: red;
    --color-hover: blue;

I even tried to put the css in app.component.scss, without success. My background is still white.