Decreases the outline level of the selected heading, and the headings that occur below the heading, by one. To only decrease the outline level of the selected heading, hold down Ctrl, and then click this icon.
将选定的标题及其下面的标题降低一个大纲级。要只降低选定标题的大纲级，请按住 Ctrl 键，然后单击此图标。