discourse-header-submenus/desktop/desktop.scss

$item-height: 40px;

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

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

  #main-outlet {
    padding-top: calc(5.8572em + #{$item-height});
  }
} @else {
  .d-header {
    top: $item-height;

    .docked & {
      top: 0;
    }
  }
}

.vmo {
  display: none;
}