Dark Theme Support

[dabockster]

Your environment

TbSync version: 4.8
Thunderbird version: 115.5.1 Prod

Expected behavior

All Settings screen text should be recolored to accommodate dark themes, or the background should change to fit into the darker theme.

Actual behavior

The Settings screen does change for the most part, but the selector bar on the top of the window is still colored with a white background. This means that it is completely unreadable on dark themes.