To Change the Symbology of the Cell Borders in a Table

You can change the symbology, that is color, line style, and line weight of the cell borders in a table.

Do one of the following:

Press <Ctrl> and select multiple cells in a table.

or
Select one or more row heading or column heading.
In the Table Tools > Layout contextual tab, in the Table Symbology group, from the Borders drop-down gallery, select the borders to which you want to apply the symbology changes.
In the Table Tools > Layout contextual tab, in the Table Symbology group, change the color , line style , or line weight .
(Optional) To apply the same symbology to other cells, select the cells and click the Borders button in the contextual tab.

The Borders button can also be used to show or hide table borders.