If you are working with tables in your PowerPoint Slides and applying custom styles, then you’d need to learn more about how to erase the borders of a table. You can do that with the Table Eraser tool.
This eraser tool is available under Table Tools -> Design menu. You can click there and then highlight with the mouse cursor the border that you want to remove.
For example, we have used this tool to erase the border of a table powerpoint template and you can see the result as follows.
Learn more how to apply styles to tables in Microsoft powerpoint 2010.