You could also be using an older version (prior 4.0.0) or a different theme (our online demos use the Material theme at the moment). Make sure your Radzen.Blazor installation is up-to-date.
That does add the white effect but by greying the rest of the page.
Still does not show the boxes around individual items and does not change the expanders which is really what I was after.
That's fine. I will live with it. Not going to re-style the entire site for a couple down chevrons.