How to change the colour of the arrows for my product gallery image when at mobile template size

Hi there, and first time posting 👋.
So, I'm experimenting with graphical elements and features on my site and I'm wanting to change the colour of the ' next/previous arrows' and  the "image number" colour on my product pages (circled in red) when in mobile format and maybe create a round background for each bit circled to sit on too. I'm hoping there's an easy way to do this but I can't work out the specific 'class'/code for each bit and I'm stuck. Any help is obviously much appreciated.
The product's image gallery is the 'simple' template, if that helps.

the url - https://www.andycropper.art/paintings/p/dormant

Add to Design > Custom CSS

@media screen and (max-width:767px) {
.ProductItem-gallery-carousel-controls .product-item-gallery-carousel-control:after {
    border-color: red !important;
}
}