Generate unique class name in css file if it referenced in JSX

I want to request a feature. Rather than having to use styleName on every element we can put it only on parent element and use existing global class. So JSX syntax will more simpler to look.

For example when I use bootstrap:
```

```
Will much simpler to look if we put styleName only on parent element:
```

```

so SCSS:
```
.container { <-- generate only this to be a unique class Name
margin: 0;
.card {
font-size: 14px;
.card-header {
background: #ddd;
}
.card-body {
background: #f8f8f8;
}
}
}
```

No source file, test, or entry point is named in the issue. Start by tracing how the Babel plugin transforms styleName and how nested SCSS class names are represented; done means parent-only styleName usage produces the requested unique class behavior for the shown Bootstrap example.

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