A NEW DEFAULT THEME FOR GTK+
This may not be such a big deal on Linux, where distributions generally have ‘their’ theme, not to mention the many packaged and readily available themes. So, basically no Linux user ever sees the default GTK+ theme. The situation is very different on other platforms, where GTK+ is often bundled with applications, and it may not be easy to install themes, or get the bundled GTK+ to use them.
For a very long time, we’ve held onto the belief that the theming system is a way to make applications blend smoothly into the platform, and that there should be a native theme for each major platform that GTK+ can run on.