HELP!!! I'm trying to center my navigation menu/bar and space out the items more

Does anyone know how to center the navigation menu and increase spacing between menu items? Also, when clicking on the drop down menu, it gives this clunky "white rectangle" appearance. Any design item to fix this?

Password to access my website is sophie. Website: https://rhino-parakeet-9xcy.squarespace.com/

Thanks so much!

Sophie

You can add this code to Website Tools (under Not Linked) > Custom CSS

.container.header-menu-nav-item {
    margin-top: 20px !important;
    margin-bottom: 40px !important;
}