Allow Modal container styles to be passed in.

## 🚀 Feature Proposal

In order to create components that appear on top of modal backdrops (like a toast/growl component), a simple solution would be another modal, but where the modal is positioned to a certain area of the screen. I can hide the backdrop and and move the modal element itself, but I can not modify the container that is full screen and prevents any presses through on web. If we could pass in container styles, then we could position this container to be only as large as its content and that would allow toast popups on top of the modal backdrop.

## Motivation

To better customize the Modal component and use it for features that are not specifically modals but require the content to be rendered as a sibling to other modals for stacking purposes.

## Example
```

This is a modal
{success &&

This is a toast

}

```