Issue title: Can't use multiple classnames
 Issue body: ```
className: `${settingsStyles.item} ${settingsStyles.toggle}`
```

Got error in console
```
discovery.umd.js:17 DOMException: Failed to execute 'add' on 'DOMTokenList': The token provided ('_4ymWhFjaYEo4wjXhK6vWF _3ueTPH3PTkN7tT_HsT0m-n') contains HTML space characters, which are not valid in tokens.
```
 Comments: 
 Comment 0: Just use array `className: [settingsStyles.item, settingsStyles.toggle]`
 Comment 1: Btw, since next release you'll able to pass a space separated class list. So your example will work
{'source': 'GithubIssues', 'repo_name_with_owner': 'discoveryjs/discovery', 'issue_id': 735156344, 'repo_stars': 243.0}