GTK3
With version 3.0, GnuCash has upgraded to the GTK3 library from GTK2.
Customization
As noted in bug 791823, there is no GTK theming tool available for GTK3 on Windows. However, this is relatively easy to resolve manually by using a CSS file and placing it at the correct location.
The overview of CSS customization of GTK3 is available at Gnome Developer site.
Sample GnuCash CSS file:
For extra info, you can also look at these low-level customizations:
Note that these contain the variables, as explained in the CSS customization overview, under Colors section.
To locate the UI elements for customization, you can use the GTK Inspector tool.
To customize the GnuCash theme, create and/or modify the Cascading Style Sheets (CSS) file. The location of this file is explained in the following entry: Where can I find the GTK resource file? Note that, by default, no gtk-3.0.css file will be created so you have to create one manually. Then add the CSS rules or copy values from an existing theme. There are plenty of GTK3 theme resources caused by the fact that CSS is a widely-adopted standard for UI styling and many people are familiar with it.
Some GTK3 theme resource sites:
etc.
Due to the lack of a dark theme, one can use the Adwaita Dark theme styling instead.
Related wiki entries:
