Can you use normal CSS with React?

it's certainly possible, you may have plain old CSS classes in a style.css somewhere, but you'll have to make sure your app includes it,

e.g. have in your App.js

import './style.css'

The standard way is to do the following;

import React, { Component } from 'react';
import './Button.css'; // Tell Webpack that Button.js uses these styles

class Button extends Component {
  render() {
    // You can use them as regular CSS styles
    return <div className="Button" />;
  }
}

See: https://github.com/facebookincubator/create-react-app/blob/master/packages/react-scripts/template/README.md#adding-a-stylesheet

1. Using CSS Modules might be better way:

CSS Modules have .module.css in their file name, like styles.module.css. Naming it so is important it avoids serious issue in plain CSS when having same CSS class names in different CSS files.

File : styles.module.css

.myClass1 {
    background-color: red;
}

File : App.js

import styles from'./styles.module.css';

<div   className={styles['myClass1']}  >
   some content
</div>

By default supported by Create React App - https://reactjs.org/docs/create-a-new-react-app.html
This can done using simple steps

npx create-react-app my-app
cd my-app
npm start

Links: . https://create-react-app.dev/docs/adding-a-css-modules-stylesheet/
. https://www.freecodecamp.org/news/how-to-style-react-apps-with-css/

2. If you want to use normal css but want more flexibilities like props to css, and open to install more dependencies then alternatives are:

. https://emotion.sh/docs/introduction
. https://styled-components.com/

Some are migrating styled-components to emotion, so may be emotion is better way to start with. See https://storybook.js.org/blog/541-components-from-styled-components-to-emotion/