Using Dark Breeze the screen locker becomes quite ugly, because the white lines of the symbol stay white and the background in the bright blue, while button and input field are dark grey. Elements in lockscreen should be excluded from theming. Reproducible: Always
@Jens, can you have a look?
There is also this problem, sandman13 pointed to in IRC: http://i.imgur.com/uwD8O9f.png So if a user wants to use a bright background, he should be able to manually change to a dark lockscreen text with (in this case!) dark input field and button.
This is fixed for the lock screen redesign in 5.13.