In the Variation Table for WooCommerce, including the quick cart where users can change the quantity, this setting controls the color of the border around the quantity input box (where users choose how many items to add to the cart), allowing you to customize it to match your site’s design and branding.

Here is the frontend show for the variation table for WooCommerce single product page.

Here is the frontend show for the quick cart carousel in WooCommerce shop page