Are apps build with gotk3 self contained?

I'm building an app for linux with gotk3. If I build it with gtk 3.3.20, will it run properly on a system with gtk 3.18? Some CSS parameters like margin doesn't work on gtk 3.3.18.

The gotk3 project uses CGO to link to gtk3 libraries on a computer (so it is not statically compiled.) The rest of your question is not Go related, but gtk3 related, as in, "what happens when a program using a later version of gtk3 is run on earlier versions of gtk3?" Realistically, probably nothing good - especially because of the sweeping changes that were made in gtk+ 3.20.

It is worth pointing out that if targetting earlier versions of gtk3 is important to you, the gotk3 github wiki addresses how to install the project in a way that targets specific earlier versions.

Thanks.