Dropdowns in Core settings have black text on dark background, theme issues

Steps

1. Connect to core
2. Choose the Material Dark or Quassel Dark theme

• Doesn't appear to happen with other dark themes, though the colors aren't always correct
• E.g. AMOLED gives settings dropdowns a lighter-than-expected background

3. Open Core settings
4. Edit a network
5. Expand the Identity dropdown

• Or pick any dropdown somewhere in Core settings, e.g. chatlist Activity level

Expected

Dropdown theming matches that of the chat list dropdown.

Actual

Dropdown uses black text on the themed background color, sometimes making it unreadable.

Example screenshot, Material Dark, black text

Example screenshot, Solarized Dark, wrong dropdown background color