Style MUI date time picker popper dialog background

I am trying to change the color of the background of the MUI date time picker’s popper for desktop and mobile :

I want to change the black / grey background to lightgreen

I have tried to use ‘popper’, ‘mobilePopper’ and ‘desktopPopper’ but none of those selectors seem to work.

Here is what I have tried that does not work :

const popperSx : SxProps = {
    "& .MuiPaper-root" : {
        backgroundColor: 'lightgreen!important', // doest not work 
    }
}

const OurDateTimePicker = ({
    value,
    setValue,
    sx,
    name,
    label,
    clearable,
    disabled,
    helperText,
    onBlur,
    error
}: OurDateTimePickerProps) => {

    const [selectedDate, setSelectedDate] = useState<Dayjs | null>(dayjs(value))

    useEffect(() => {
        setSelectedDate(dayjs(value))
    }, [value])

    const handleSelectedDate = (newValue: Dayjs | null) => {
        setSelectedDate(newValue)
        if (newValue)
            setValue(new Date(newValue.format('YYYY-MM-DDTHH:mm:ss')))
    }

    const [cleared, setCleared] = useState<boolean>(false)

    useEffect(() => {
        if (cleared) {
            setValue(null)
            const timeout = setTimeout(() => {
                setCleared(false)
            }, 1500)

            return () => clearTimeout(timeout)
        }
        return () => { }
    }, [cleared])

    const handleBlurWrapper = (event: React.FocusEvent<HTMLInputElement | HTMLTextAreaElement>) => {
        onBlur?.(event);
    }

    return (
        <Box sx={sx}>
            <LocalizationProvider
                dateAdapter={AdapterDayjs}
                adapterLocale={"fr"}
                localeText={frFR.components.MuiLocalizationProvider.defaultProps.localeText}>
                <DateTimePicker
                    name={name}
                    value={selectedDate}
                    onChange={handleSelectedDate}
                    sx={{ width: "100%" }}
                    label={label}
                    slotProps={{
                        field: { clearable: clearable, onClear: () => setCleared(true) },
                        textField: {
                            helperText: helperText,
                            error: error,
                            onBlur: handleBlurWrapper,
                        },
                        mobilePaper: popperSx,
                        desktopPaper: popperSx,
                        popper: popperSx

                    }}
                    disabled={disabled}
                />
            </LocalizationProvider>
        </Box>
    )
}