Hi,
You have to make some changes in coding
in file template\blocks\product_list.tpl after line 32 which is <div class="col-md-3 col-sm-6 col-xs-12">
add one more div like <div class="display-border"> right after it and add </div> on line 80
Do the same thing in template\pages\product\product_listing.tpl
now add css for this class=display-border in style.css so go to stylesheet\style.css
.display-border{
border: 3px solid #e5e5e5;
border-radius: 19px;
padding: 2px 2px 2px 2px;
}
Note: You can edit the styling-color as per your requirement