A vertical MudDivider is not shown in my razor page

Its a blazor wasm .net 9 app with mudblazor 8.0.0. The following code works onhttps://try.mudblazor.combut not in my razor page.

<MudStack Class="d-flex pa-4" Row="true"><MudIconButton Icon="@Icons.Material.Filled.Save" Variant="Variant.Outlined" Color="Color.Primary" Size="Size.Large" /><MudIconButton Icon="@Icons.Material.Filled.Delete" Variant="Variant.Outlined" Color="Color.Primary" Size="Size.Large" /><MudDivider Vertical="true" FlexItem="true" /><MudIconButton Icon="@Icons.Material.Filled.Help" Variant="Variant.Outlined" Color="Color.Primary" Size="Size.Large" /></MudStack>