How to change the color of the Header buttons on FullClaendar using makeStyles on material-ui?

Question

I am new in react and frontend styling. I have FullCalendar component and I need to change the buttons colour and icon.

    const classes = useStyles();              

         return (
           <DialogContent>
            <Fullcalendar
              themeSystem="bootstrap"
              initialView="dayGridMonth"
              headerToolbar={{
                start: "today,prev,next",
                center: "title"
              }}
              height={"90vh"} 
              events={calendarEvents}
            />
          </DialogContent>
         )

the style.js for this is:

export const useStyles = makeStyles((theme) => ({
  
  calendarHeader: {
    background: RGB(255, 255, 0)
  }
}));