On start and exit tour, elements with z-index are highlighted

When start and exit/complete tour, DOM elements that have z-index > 0 are highlighted.

If I remove the scss rule 
```
.introjs-tour {
    transition: opacity 0.3s ease-out;
} 
```
no more problem BUT it doesn't look smooth as before.

You can see it in live on official website: when click on "Run example", the header bar is highlighted.

Can you provide some fix ?

