Как добавить класс элементу в React.js?

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import React, { useState } from "react";
import ReactDOM from "react-dom";

const Contact = () => {
  const [className, setClassName] = useState("");
  const [inputValue, setInputValue] = useState("");

  return (
    <div>
      <p className={className}>Текстовый блок</p>
      <input
        type="text"
        value={inputValue}
        placeholder="Класс"
        onChange={(e) => setInputValue(e.target.value)}
      />
      <button
        onClick={() => {
          setClassName(`${inputValue} ${className}`.trim());
          setInputValue("");
        }}
      >
        Добавить класс
      </button>
    </div>
  );
};

class App extends React.Component {
  render() {
    return <Contact />;
  }
}

ReactDOM.render(<App />, document.getElementById("container"));

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const MyComponent = () => {
  return Hello, world!;
};

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import { useRef } from "react";

const MyComponent = () => {
  const myRef = useRef(null);

  const handleClick = () => {
    myRef.current.classList.add("my-class");
  };

  return (
    <>
      Click me!
      Add class
    
  );
};