Using the Right-Click Pop Up Menu
You can also change the style of the borders of individual
cells (or groups of cells) in your table by right-clicking on the selected area, and choosing Grid Line Style,
Grid Line Thickness, or Grid Line Color
from the pop-up menu.
If you select None from the Grid Line Thickness sub-menu, your chosen grid lines will become invisible. To edit only one specific grid line, move your cursor over the grid line until your cursor changes to the Grid Line Selection Cursor.
Click on the grid line to select it. Then right-click to bring up a pop-up menu, and choose either Grid Line Style, Grid Line Thickness, or Grid Line Color to customize the line.