Hi Emla-
Thanks for reaching out. We’re not the developers of the Storefront Theme, but we’re happy to help out.
It looks like the extra whitespace is being caused by the padding around the actual menu items in both your navigation menu as well as your cart. I was able to remove it with these rules:
div.primary-navigation a {
padding-bottom: 0px !important;
}
.site-header-cart .cart-contents {
padding-bottom: 0px !important;
}