I try to theme the unity lightdm greeter and I've succeeded in doing so by looking at the source code and the Ambiance .css files. One thing I'm not able to theme however is shown in this short video, and screenshot.
When entering a wrong password the greeter tries to log in and fails of course. The problem is that while the greeter tries to log in the button in the top right corner becomes white and the emblem becomes invisible.
I know to theme the button (it is the option-button class) but I don't know how to find out which state the widget is in exactly when entering a wrong password; because this would enable to change its appearance by modifying the css file.
For reference: I'm trying to modify this file here(the repsective definitions are in the last few lines): https://github.com/shimmerproject/Numix/blob/master/gtk-3.0/scss/apps/_unity-greeter.scss
Best Answer
Ok, it is completely not obvious but I found out how to theme this specific widget state of the button.
This
does the trick.