Use css attributes for HTML code in the React JS app code. Here is the sample code of css usage for styling the react app.
Instead of classname="heading" , className="heading" is used
React JS Code – CSS Usage
index.js
import React from "react";
import ReactDOM from "react-dom";
ReactDOM.render(
<div>
<h1 className="heading"
contentEditable="true"
spellCheck="false">My Favourite Foods</h1>
<ul>
<li>Bacon</li>
<li>Jamon</li>
<li>Noodles</li>
</ul>
</div>,
document.getElementById("root")
);
style.css
.heading{
color:red
}
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<title>JSX</title>
<link rel="stylesheet" href="styles.css" />
</head>
<body>
<div id="root"></div>
<script src="../src/index.js" type="text/JSX"></script>
</body>
</html>
