Gtk city dialog popups use variable-width font (because of nonexistent style "city_info_label")
The explanatory popups on the city dialog showing e.g. where trade points come from use fixed-width formatting, but in the Gtk clients, they are displayed with a variable-pitch font, so they end up poorly aligned.
This is because they use a nonexistent style "city_info_label", set with
gtk_widget_set_name(label, "city_info_label"). In general, these widgets names are joined up with the font option 'target' names in options.c, via the style definition in
gui_update_font(). But, there is no option with the target name "city_info_label".
I'm inclined to just set it to "city_label", the same fixed-width style used for the text on which you click to get these popups. Screenshots show before/after of Gtk3 client (Gtk2 and Gtk3.22 are similar).
(The Happiness tab popups have a similar issue, with nonexistent style name "city_happiness_label". But since the happiness popups don't rely on fixed-width formatting, I'm inclined not to change them to a fixed-width font. Perhaps we can just remove the style name, but I've left it for now, with a comment.)