Add styling to defaultValue in textarea in React

I am using a Material UI React component called TextareaAutosize:

<TextareaAutosize
  minRows={2}
  style={resize: 'none'}
  defaultValue={<span style={{fontSize: "20px", color: "blue"}}>Content Body</span>}
/>

Instead of getting Content Body in the TextareaAutosize component, I'm getting this as the default value:

How do I add styling to the defaultValue?

Edit code on Stack Blitz: https://stackblitz.com/edit/react-fnx6we?file=demo.js

EDIT: For clarification, I want ONLY the defaultValue to have the styling I applied. When the user starts typing or removes the defaultValue and starts typing, the styling of the defaultValue should NOT be applied.

defaultValue parameter accepts String values only. Use parameter style to define additional styling. Or use jss like styling for components (check @mui/styles) EDIT: to change styling of the element "on the fly" you will need to use additional variables and functions. Check demo on code on Stack Blitz.

import React, { useState } from 'react';
import TextareaAutosize from '@mui/material/TextareaAutosize';
import { makeStyles } from '@mui/styles';

const useStyles = makeStyles({
  textAreaWithStyle: {
    background: 'linear-gradient(45deg, #FE6B8B 30%, #FF8E53 90%)',
    border: 0,
    borderRadius: 3,
    boxShadow: '0 3px 5px 2px rgba(255, 105, 135, .3)',
    color: 'white',
    height: 48,
    padding: '0 30px',
    fontSize: '20px',
    color: 'blue',
    resize: 'none',
  },
  textAreaWithoutStyle: {
    resize: 'none',
  },
});

export default function MaxHeightTextarea() {
  const classes = useStyles();
  const [valueOfInput, setValueOfInput] = useState('Default Text');

  const returnStyleBasedOnInput = () => {
    if (valueOfInput === 'Default Text') {
      return classes.textAreaWithStyle;
    } else {
      return classes.textAreaWithoutStyle;
    }
  };

  const checkIfDefaultValueInTextAreaAndRemooveIt = () => {
    if (valueOfInput === 'Default Text') {
      setValueOfInput('');
    }
  };

  const onInputChange = (e) => {
    setValueOfInput(e.target.value);
  };

  return (
    <TextareaAutosize
      maxRows={4}
      className={returnStyleBasedOnInput()}
      value={valueOfInput}
      onChange={onInputChange}
      onClick={checkIfDefaultValueInTextAreaAndRemooveIt}
    />
  );
}

Edit code on Stack Blitz: https://stackblitz.com/edit/react-fnx6we-3vdn7i?file=demo.js