You can use this code to Custom CSS box. It will change Portfolio Pagination Color in Squarespace.
/* Pagination */
.item-pagination[data-collection-type^="portfolio"], .item-pagination[data-collection-type^="portfolio"] {
background-color: black;
}
.item-pagination[data-collection-type^="portfolio"] * {
color: white !important;
fill: white;
}
Result:
