React Material UI TextField FormHelperTextProps Styling Not Working

Question

I'm trying to style the helper text that comes with the TextField Component given by Material UI ( found here). I'm using FormHelperTextProps (found here). However, it seems that, for some reason, the styling I'm writing is not being applied to the component itself. I would appreciate any help I could get on this. Here is my code:

    const useHelperTextStyles = makeStyles(()=> ({
    root: { 
        "& .MuiFormHelperText-root" : { color: TextFieldColours.error["status-text"] }, 
        // "& .MuiFormHelperText-contained"
    }
    })
     );

    const EmptyTextField = (props: CustomEmptyFieldProps) => {
    const {
         usernameOrPass,
    } = props; 
    const inputLabel = "VolunteerHub " + usernameOrPass; 
    const errorMessage = "Please enter your VolunteerHub " + usernameOrPass; 

    const textFieldStyles = useTextFieldStyles(false);
    const helperTextStyles = useHelperTextStyles(); 
    return (
        <div>
            <TextField
                className={textFieldStyles.root}
                placeholder={inputLabel}
                id="outlined-error-helper-text"
                defaultValue=""
                helperText={errorMessage}
                variant="outlined"
                FormHelperTextProps={{
                    classes={helperTextStyles.helperText,}
                }}
            />
        </div >
    );
}

Answer 1

first of all a class needs to targetted in classes prop, like root, focused etc. so in classes props select pass the style to the root class. And another issue is there is no helperText class in useHelperTextStyles hook.
So for targeting the root style the code will like this:

const useHelperTextStyles = makeStyles(() => ({
    root: {
        color: TextFieldColours.error["status-text"]
    }
}));

const EmptyTextField = (props) => {
    const { usernameOrPass } = props;
    const inputLabel = "VolunteerHub " + usernameOrPass;
    const errorMessage = "Please enter your VolunteerHub " + usernameOrPass;

    const textFieldStyles = useTextFieldStyles(false);
    const helperTextStyles = useHelperTextStyles();
    return (
        <div>
            <TextField
                className={textFieldStyles.root}
                placeholder={inputLabel}
                id="outlined-error-helper-text"
                defaultValue=""
                helperText={errorMessage}
                variant="outlined"
                FormHelperTextProps={{
                        classes:{
                            root:helperTextStyles.root
                        }
                }}
            />
        </div>
    );
};

Here is a working demo: