How to find code that causes a 'deprecated' warning?

[Chris Green]

I am getting the following warning from a program I have just
converted from gtk 2 to gtk 3 :-

(abook:58240): Gtk-WARNING **: 12:01:58.064: Theme parsing error:
gtk.css:66:28: The :prelight pseudo-class is deprecated. Use :hover
instead.

How do I find what is causing the warning?  I'm not using the prelight
pseudo-class directly in my code anywhere.

-- 
Chris Green
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