Участник:StasFomin/GTK/GTK-and-spacing-in-GTK-HeaderBar

I want to make new Client Side Decoration buttons compatible with my metacity themes.

In my metacity themes I have three compact button (minimize, maximize, close) like that:

With lot of CSS I get

You can see ugly unremovable spacing between titlebuttons.

This is because of «spacing=6» in parent GTKBox:

How to remove this spacing by the GTK CSS?

I look in /gtk+3.0/gtk+-3.12.2/gtk/gtkheaderbar.c and this spacing inherited from internal spacing of GtkHeaderBar (with hardcoded «#define DEFAULT_SPACING 6»)

But there is the function «gtk_header_bar_set_property»,

so may be there is some CSS Property like

«-GtkHeaderBar-spacing» or something else?

Please, give me any idea how to fix it without patching GTK.