Comment 1 for bug 829218

That's because Abiword is still a GTK2 application, so it uses the old theme. In order to solve this issue, it is necessary to do some changes to the GTK2 theme as well. The code is already available on the "Light Themes Evolution", which I maintain.

I'm willing to push a branch with all the adaptations required if asked. The code is free, anyway :D