Hello,

Please remove the previous Custom CSS for icons and try adding the following Custom CSS in the Global Custom CSS area under Theme Settings >> Custom CSS.

.hasno-product-count .category-nav-link .category-icon {
	max-height: 40px;
}

And I have visited your website and the background-size is already covered.

Screenshot for Clarification: https://ibb.co/tBV2gxR

Regard’s.
Xtemos Studios.