The plot area of a chart is the area where the data series, axes and gridlines are drawn.
Changing properties: To change the properties of the plot area, select it, right-click it and choose the command Plot area: Properties from the context menu.
Tip: Alternatively, you can choose this command via the Edit properties icon 
on the ribbon tab Chart | group Chart elements. The other alternative is to double-click on the plot area.
You can make the following settings:
Format tab
Tip: Borders and fill can also be conveniently adjusted directly via the buttons of the ribbon tab Chart | group Chart elements. For more information, see Editing chart elements.
▪Border section
| Here, you can add a border to the plot area. To do so, use the option Custom to select the desired line style. The option None removes the border. |
▪Fill section
| Here, you can change the fill of the plot area. To do so, use the option Color to select the desired fill color. The fill will be transparent if you use the option None. |
| If you select the fill type Effects and click on the Customize button, the program will display a dialog box that will allow you to also apply more complex fills (such as a color gradient). The use of this dialog box is described in Object properties, Fill tab. |