navigation_test.links.menu.yml

navigation_test.navigation__custom_item:
  title: "Test Custom Icon"
  weight: 0
  menu_name: admin
  parent: system.admin
  route_name: "<front>"
  options:
    icon:
      pack_id: navigation_test
      icon_id: star
      settings:
        class: 'toolbar-button__icon foo'
        size: 25

navigation_test.navigation__default_item:
  title: "Test Default Icon"
  weight: 1
  menu_name: admin
  parent: system.admin
  route_name: "<front>"
  options:
    icon:
      icon_id: pencil

navigation_test.navigation__no_icon:
  title: "Test No Icon"
  weight: 2
  menu_name: admin
  parent: system.admin
  route_name: "<front>"

navigation.media:
  title: "Test Default Logic Icon"
  weight: 3
  menu_name: admin
  parent: system.admin
  route_name: "<front>"