Fullscreen Overlay

Hey there, loving this component

Is there an "easy" way to get a fullscreen overlay?  I am currently using a loader from elementUI which provides a fullscreen option (see code below).  Is this something available? I could not find anything in the docs.

```vue
<div v-loading.fullscreen.lock="isLoading" element-loading-background="rgba(0, 0, 0, 0.1)">
 ...app code here
</div>
```
