we added GTK3 now to support GTK3 application theming under XFCE.
The easiest way to download and apply GTK3 themes under XFCE is to try the Opendesktop app:
Just give it a shot and let us know how it works.
Thanks for introducing gtk3 on xfce-look.org. As for the app, i’m old school, i hate apps, i like it in the browser