There are a lot of xfwm themes that look really good when you have a light theme(like Adwaita) enabled, but look quite bad when a dark theme(like Advaita-Dark) is enabled. A great example of this is the Gtk and cruxish xfwm4 themes. They look really good in a light theme, but the window close, hide, maximise buttons are near impossible to see on dark themes like Advaita-Dark and Mantis, so I have modified these themes to look better on dark themes.
Themes Present:
Just clone this repository and copy the folders to the ~/.themes folder. If you do not have one, you can create it. If you want these themes system wide, you need to copy these folders to the /usr/share/themes folder.