This is RAVEfinity's work (www.ravefinity.com/p/ambiance-radiance-for-xfce-lxde.html) with a fix for ugly-looking GTK3 applications.
Just by chance, I took the GTK3 folder from the preinstalled Ambiance theme in my /usr/share/themes folder, and used it to replace the GTK3 folder in RAVEfinity's theme. This solved the problem with GTK3 applications not liking RAVEfinity's version of Ambiance, and now all apps look great!!! No ugly-looking GTK3 apps anymore!!
Let me know if it works for you.
You can see the screenshot. Thunar, Brasero and Totem all are correctly themed. And the XFCE panel looks great, too.
INSTALL: Extract the zip file into /usr/share/themes. You need to open pcmanfm or thunar with root privileges to do that. In the terminal, sudo pcmanfm (for LXDE) or sudo thunar (for XFCE). Then choose this theme from your appearance manager.