first of all, I really like the AddOn and it does a great job!
I am using Thunderbird with a dark theme (TT DeepDark). When I open the CardBook tab and select one of my contacts, the details panel on the right shows the information, that I am looking for, but it applies some custom coloring to the user interface that causes the text to appear in a bad contrast to the background.
This also happens when I open the contact editor. I added two images to show the effect.
Do you think there is a way to remove the custom coloring of the user interface, so the dark theme can be applied consistently?