Cursor: Custom zoom-in icon

Before:

After:

Code:

/* -- code to use a custom zoom cursor -- */
.mfp-zoom,.product__photo img[data-mfp-src] {
    cursor: url(https://cdn.shopify.com/s/files/1/2018/8867/files/zoom-in-clear.png), auto;
}
/* - end - */

You can upload your own transparent .PNG to the the Shopify file manage and use the URL from there:

https://shopify.com/admin/settings/files

Where do I add the code?

Use this link to learn where exactly to add this code snippet:

Where to add your CSS style code