A SeparatorToolItem is a ToolItem that separates groups of other ToolItems.
Depending on the theme, a SeparatorToolItem will often look like a vertical line on horizontally docked toolbars.
If the Toolbar child property “expand” is true and the property draw is false, a SeparatorToolItem will act as a “spring” that forces other items to the ends of the toolbar.
Use SeparatorToolItem to create a new SeparatorToolItem.
GtkSeparatorToolItem has a single CSS node with name separator.