Spinner: Nothing is displayed

[mmtr]

Describe the bug
When rendering a Spinner component outside Gutenberg, nothing is displayed. Actually, a div with the spinner and is-active classes is rendered, but these classes are not giving any style at all.

To Reproduce
Execute the code below in a new React project after installing @wordpress/components.

import React from 'react';
import ReactDOM from 'react-dom';
import { Spinner } from '@wordpress/components';

import '@wordpress/components/build-style/styles.css';

const MySpinner = () => (
	<Spinner />
);

ReactDOM.render(
	<MySpinner />,
	document.getElementById( 'root' )
);

Expected behavior
A spinner should appear.

Desktop:

• OS: macOS High Sierra
• Browser: Chrome
• Version: 67

Additional context
Issue found while working on #8338 and Automattic/wp-calypso#26367

[youknowriad]

I think we should do the same we did for the button component: Avoid relying on WordPress Core Styles for the spinner component and copy those styles to Gutenberg itself.