Why GVim doesn't use dark theme?

I want to make the *interface* of GVim to use dark theme. I have the following line in my ~/.config/gtk-3.0/settings.ini:

[Settings]
gtk-application-prefer-dark-theme=1

All my GTK apps use dark theme but for some reason GVim still uses a light theme. How can I change that? Note: When I run gvim --version the following line is in the result: Huge version with GTK3 GUI. So I'm sure it's using GTK3.