You can add a border around cells to emphasize data, mark summarized values, or separate data in cell ranges. To quickly add an outside border, select the cells that you want included, and press Ctrl+Shift+7.
Here's how you can add borders by selecting different line styles and colors:
Select the cell or range of cells.
On the Home tab, click the arrow next to Borders, and then choose the border options that you want.
Tip: The Borders button shows the most recently used border style. To apply the same style, click the Borders button (not the arrow).
To remove a border, select the cells with the border and click the arrow next to Borders > No Border.