I'm trying to set the height of a div to be the full screen height minus the heights of other variables, such as the page banner and page notification. However the page notification isn't always present in some pages and so therefore the height calculation is not working on pages where there is no page notification.
How could I tell CSS to calculate the value of the height, and if the variable page-notification-height is not defined then to just ignore it or set the value to 0?
.div {
height: calc(100vh - var(page-banner-height) - var(page-notificaton-height));
}