How do you apply multiple CSS classes in React?

In React, you can apply multiple CSS classes to an element by using the `className` attribute. The `className` attribute accepts a string that contains one or more space-separated class names. Here's an example:

```jsx
import React from 'react';
import './YourComponent.css'; // Import your CSS file if using external styles

const YourComponent = () => {
  return (
    <div className="class1 class2 class3">
      {/* Your component content */}
    </div>
  );
};

export default YourComponent;
```

In this example:

1. We have a `div` element with the `className` attribute.
2. The `className` attribute is assigned a string that contains three class names separated by spaces: `"class1 class2 class3"`.
3. Each of the individual classes represents a different CSS class that you want to apply to the element.

If you are using an external CSS file (like `YourComponent.css` in the example), make sure to import it at the beginning of your component file.

If you want to conditionally apply classes based on some logic, you can use JavaScript expressions within the `className` attribute:

```jsx
import React from 'react';

const YourComponent = ({ condition }) => {
  return (
    <div className={`base-class ${condition ? 'additional-class' : ''}`}>
      {/* Your component content */}
    </div>
  );
};

export default YourComponent;
```

In this example, the `additional-class` will be added to the `div` if `condition` is true.

Remember that the `className` attribute is used in React to avoid conflicts with the JavaScript `class` keyword. This is a common pattern used in React development to apply styles dynamically to components.