Hello!

I noticed this library doesn't work on elements that are slotted inside containers that are in a shadow DOM. Here's a simple case where you can see it doesn't work: https://codepen.io/remiscan/pen/ogNVOWQ

(And here's an equivalent case without the shadow DOM, that works: https://codepen.io/remiscan/pen/LEYavyg).

I'll make a pull request with a fix :)