evince reports gtk theme-parsing errors - how can I fix them?

Question

I use Lubuntu 16.10. When I run evince (from a shell), I get multiple error messages such as:

(evince:14128): Gtk-WARNING **: Theme parsing error: gtk-lubuntu.css:190:21: The :insensitive pseudo-class is deprecated. Use :disabled instead.

as well as:

(evince:17673): Gtk-WARNING **: Theme directory  imported-Humanity/192 of theme Lubuntu has no size field
(evince:17673): Gtk-WARNING **: Allocating size to EvSidebar 0x562e8f3ee310 without calling gtk_widget_get_preferred_width/height(). How does the code know the size to allocate?

What can I do about these errors? They're annoying!

Answer 1

A partial answer:

For the first kind of errors (and some other CSS-syntax-change-related errors), you can edit /usr/share/themes/Lubuntu-default/gtk-3.0/ and make batch replacements of the deprecated pseudo-element names or property names with the up-to-date names. That avoids the vast majority of the errors on the console but not the last two that are listed in the question.