Hello,
On Debian testing, when GNOME is using a dark theme, Geany seems to have the inverted behavior of the screenshots already present in this issue, ie. the widgets are correctly black but the default theme is white.
The [“gtk-application-prefer-dark-theme” property](https://developer.gnome.org/gtk3/stable/GtkSettings.html) could be used to determine if the current theme is light or dark, to select a better default theme given the user’s preferences context.