Change button colour when selected

Hi all - it’s not clear to me how to change the buttons colour when selected?

For context, we have a multiple choice page. I want the user to select multiple buttons before clicking ‘next’. I can’t work out how to have the button change colour once selected by the user?

If you scroll down the Style section (left panel), you can see the styling options for an element. These include when Selected. Also, the Button Group element might be more fit here than standalone buttons.