You can use predefined cell border or create a custom cell border to enhance your worksheet's appearance.
1. Select the cell or range of cells that you want to add a border to.
2. On the [Home] tab, in the [Font] group, click the arrow next to the border.
3. Select your option from the list as shown in diagram at the side:
How to apply a custom border style or a diagonal border:
1. Click [More Borders], the [Format Cells] dialog box appears.
2. On the [Border] tab, under [Line] and [Color], select the line style and color that you want.
3. Under [Presets] and [Border], click one or more buttons to indicate the border placement.
(see diagram below)