Ok, so that's easy. Between each box, there is a cell, but without any border. So for that, I go in Step 4 - Design Grid, I select the cell, Edit Styles, Edit Styles for: This Cell (or this row if you have more than 1 column), Check Border Size and select 0. And i ofter also change the height of the cell with Padding (Vert). If you have another question, don't hesitate :)