I use Arch Linux with i3WM. In i3 some of the windows and their menus look fine but in applications like Eclipse and Transmission, it makes weird unseparated tool bars.
There is no such an issue in Ubuntu (+ i3wm). Any solutions?
The recent GTK 3.20 update has broken a lot of themes; until such time as they are updated to work with the new API, you will need to use a standard theme (like Adwaita) that is compatible with the new version.