Material UI Toggle Button - can't change background color when selected

Question

I'm trying to use the Material UI Toggle Button kind of like a radio button to give the user 2 choices to a given question.

It's functioning mostly as expected, but when trying to adjust the style for when each toggle button is selected, I can't get the Toggle Button background color to change. I'm using the classes prop on the ToggleButton component, and using the "selected" rule within that prop. Certain css properties (such as padding & boxShadow) are working, but others (including backgroundColor) are not. My goal is to make the Toggle button have a blue background when selected, but so far I can't get it to display differently than the darker grey background when selected.

I'm using React, along with Formik and Formik-Material-UI. Here is my code:

const useStyles = makeStyles((theme) => ({
  toggleButton: {
    backgroundColor: 'blue',
    border: [10, 'solid', 'black'],
    padding: 10,
    boxShadow: [
      [0, 0, 0, 1, 'blue'],
    ],

  }
}));

export function ScheduleAndServices(props) {
  const classes = useStyles(props);

return (

            <Field 
              component={ToggleButtonGroup} 
              name="requestType" 
              type="checkbox" 
              exclusive
            >
              <ToggleButton 
                value="ps" 
                aria-label="Temporary/Occasional" 
                selected={values.requestType === "ps" ? true : false}
                classes={{selected: classes.toggleButton}}
              >Temporary/Occasional   
              </ToggleButton>
              
              <ToggleButton 
                value="reg" 
                aria-label="Regular"
                selected={values.requestType === "reg" ? true : false}
              >Regular
              </ToggleButton>
            </Field>
);
}

Answer 1

  const useStyles = makeStyles(theme => ({
    ToggleButton : {
        '&.MuiToggleButton-root.Mui-selected': {
            backgroundColor: theme.palette.common.white,
        }
    }
}));