Add a class to the dialog container

Seems like my change was somehow committed to the 1.0.x branch, rather than the issue fork? How is that possible?

It was committed to the "issue fork" of the original code repo.

In any case, I agree it would be helpful to have a class here. In my case, I want to change the opacity of the background overlay, but only when this specific dialog is used.

Thanks for the MR. Committed now.