change product image gallery arrow thickness

I'd like to make the arrows in my product image galleries thicker. I tried adding the following code to my CSS but with no luck.
https://www.rowac.com/de/shop/p/seat-top-round

.ProductItem-gallery-carousel-controls .product-item-gallery-carousel-control:after 

{
    stroke-width: .1rem !important;
}

Add to Design > Custom CSS

.ProductItem-gallery-carousel-controls .product-item-gallery-carousel-control.ProductItem-gallery-next:after, .ProductItem-gallery-carousel-controls .product-item-gallery-carousel-control.ProductItem-gallery-prev:after {
    border-width: 4px 4px 0 0 !important;
}

@tuanphan You seriously are the best!  How about changing the color to black? 

@NerdvillebyJenMaher Hi! To change the color of the product image gallery arrow, add this code under the Custom CSS panel:

.ProductItem .product-item-gallery-carousel-control::after {
    border-color: #000 !important;
}