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.
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.