XFCE 4.14 gtk3 theming

Hi,
XFCE 4.14 changes some things, and I need to modify my home made custom theme.

I can't find the necessary documentation for understand what I've to add or modify.

The main thing that I want to modify is the xfce4-panel's tasklist plugin

But I'd like to have a most complete documentation

you have to wait a little
https://www.xfce.org/about/tour