See Also
The background of a oneline diagram can display triangles among other items.
Edit Mode
To add a new triangle, first go to the Draw ribbon tab and select Insert > Background Triangle from the Individual Insert ribbon group. Position the cursor where you would like to place the upper left-hand corner of the rectangle and click with the left mouse button. A triangle having the default size is inserted. Drag the triangle's resizing handles to resize/reshape the rectangle.
To resize or reshape an existing triangle, click on it to select it. The resizing handles will appear, which you can then drag to reshape or resize the rectangle.
To change the color, line thickness or fill color of the rectangle, first select the triangle by clicking on it on the diagram, and then use the tools in the Formatting ribbon group on the Draw ribbon tab, or right-click on it and select Format Background Triangle from the local menu.