Basic question about Gateway port definitions

Networking
1

I have an example istio cluster on AKS with the default ingress gateway. Everything works as expected I’m just trying to understand how. The Gateway is defined like so:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: my-gateway
  namespace: some-config-namespace
spec:
  selector:
    app: istio-ingressgateway
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - uk.bookinfo.com
    - eu.bookinfo.com
    tls:
      httpsRedirect: true # sends 301 redirect for http requests
  - port:
      number: 443
      name: https-443
      protocol: HTTPS
    hosts:
    - uk.bookinfo.com
    - eu.bookinfo.com
    tls:
      mode: SIMPLE # enables HTTPS on this port
      serverCertificate: /etc/certs/servercert.pem
      privateKey: /etc/certs/privatekey.pem

Reaching the site on https://uk.bookinfo.com works fine. However when I look at the LB and Service that goes to the ingressgateway pods I see this:

LB-IP:443 -> CLUSTER-IP:443 -> istio-ingressgateway:8443

kind: Service
spec:
  ports:
    - name: http2
      protocol: TCP
      port: 80
      targetPort: 8080
      nodePort: 30804
    - name: https
      protocol: TCP
      port: 443
      targetPort: 8443
      nodePort: 31843
  selector:
    app: istio-ingressgateway
    istio: ingressgateway
  clusterIP: 10.2.138.74
  type: LoadBalancer

Since the targetPort for the istio-ingressgateway pods is 8443 then how does the Gateway definition work which defines a port number as 443?