Chrome Version: 59.0.3066.0
OS: Linux

It seems gtk_style_context_set_path does not copy classes for the context so we have to do it manually. It can be observed in debugger (or with proper logs) in AppendCssNodeToStyleContext. It causes - for example - DCHECK in gtk_util.cc : 569 (DCHECK(ContextHasClass(context, "vertical"));) as context doesn't have any class set (neither "horizontal" nor "vertical").