Thickness FormatProperties.MarginOuter margin padding. The margin forms a invisible padding layer to an object. The size of the margin is not subtracted from the object's size, but contributes to the amount of space that the object occupies in a container. Example = HBox(null, null, new Edge(3, 0, 90%)) { VAlign: Top; Box; // No margin Box {Margin: 10}; // Same size all around Box {Margin: new Thickness(0, 5, 20, 10)};};