Nested vue-virtual-scroller components CSS conflict

Thanks for this awesome component, first of all.

I'm integrating it currently in my project, where I do have the need to leverage it nested in with two different configurations:

- First instance running a horizontal instance.
- Per each element of the horizontal list, I'm also needing a vertical instance.

As you could imagine, that's due the fact I need to render a massive amount of nodes, in a structure like follows:

```js
const data = [{
title: 'Example',
flags: [true, false, true, false],
data: [{
title: 'Sub example',
flags: [true, false, true, false]
}]
}];
```

The first level could be thousands of elements, and per each individual, thousands of them.

The issue I'm facing, though, is the following:

The library styles is applying styles with nested selectors, therefore the vertical list (level 1 data) is getting the styles from the level 0 list (regardless it's set in vertical mode, and the styles from the parent is horizontal).

Any hints on ☝️?

Thanks in advance.