Try putting this code into main.css
Code:
.products products-table width-100 .product-cell {
border-right-width: thin;
border-left-width: thin;
border-right-style: solid;
border-left-style: solid;
border-right-color: #CCCCCC;
border-left-color: #CCCCCC;
}
if that works, you'll be able to change css to whatever you want to style it. Your template is different from mine and your featured products table doesn't have an id so its a little difficult to control it with css.