Dialogs and the Lumo Dark theme

I am using the Lumo Dark theme, which is mostly good.

But the styling for Dialogs is just not good. Basically, the problem is - I think - that the standard Dialog code makes the background darker in order for the Dialog to stand out in contrast. That works fine for light colored backgrounds. But the background in Lumo Dark is already dark, and so basically a normal human can barely tell where the dialog is - it all blends in and just does not look right.

Also, why do I need a PhD in CSS and Vaadin in order to customize the styling for a dialog’s background. I am 4 hours in of Googling and trying 25 different ways to make this work, all to no avail. So I am giving up for now - I have to get some actual application code done.