Applying CSS box model to GTK+
Among all the properties in CSS box model,
- only GtkBorder is present in GTK.
- property padding is on list of TODO, AFAIK.
- property margin is missing 'til this time.
GtkAlignment was said to implement padding. Why not GtkContainer?
GtkContainer has ::set_border_width API. But the argument is not a GtkBorder but a integer. ::set_border with GtkBorder must implemented.