The Borders and Shading box has many options.
Borders and shading are a part of a table's style. Even if you may have already selected a table's style, you can modify borders or shading. You can apply borders or shading to the entire table, individual cells, or even individual paragraphs within a table.
To remove or change the borders of a table, cell, or group of cells, highlight the cells and open the Borders list in the Table Styles group of the Design tab. Select from the buttons to make a change or click Borders and Shading.
In the Borders and Shading box, pay careful attention to the Apply to list. The Apply to options vary, depending on what table parts you've selected. If you accidentally selected a cell, but wanted to apply a border for the entire table, you can change the selection in the Apply to list.