/templates/catalog/_partials/miniatures/product.tpl

<div style="text-align: center; margin: 3px;">
    	<form action="{$urls.pages.cart}" method="post" id="add-to-cart-or-refresh">	
          <input type="hidden" name="token" value="{$static_token}">
          <input type="hidden" name="id_product" value="{$product.id}" id="product_page_product_id">
          <button class="btn btn-primary add-to-cart {if $product.quantity < 1}out-of-stock{/if}" data-button-action="add-to-cart" type="submit">
                   <i class="material-icons shopping-cart">shopping_cart</i>
                   {l s='Add to cart' d='Shop.Theme.Actions'}
          </button>
  		</form>
</div>