discourse-header-submenus/desktop/desktop.scss

$item-height: 40px;

@if $Fixed_mode == "true" {
  .header-submenus {
    position: sticky;
    top: 0;
    z-index: z("header") + 1;
  }

  .d-header-wrap {
    top: $item-height;
  }

  #main-outlet {
    padding-top: calc(1.8em + #{$item-height});
  }

  // need to include the menu height in the header offset
  // then update the header offset where used in core for sidebar and chat
  :root {
    --header-offset-with-submenu: calc(
      var(--header-offset, 0px) + #{$item-height}
    );
  }

  .sidebar-wrapper {
    top: var(--header-offset-with-submenu);
    height: calc(100vh - var(--header-offset-with-submenu, 0px));
  }

  html.has-full-page-chat body #main-outlet {
    max-height: calc(
      var(--chat-vh, 1vh) *
        100 -
        var(--header-offset-with-submenu, 0px) -
        var(--composer-height, 0px)
    );
  }
}

.top-menu {
  .menu-item.vmo {
    display: none;
  }
}