node styling via CSS

[<emixp AT gmx.net>]

Hello, 

I am currently playing around with a minimal application which just creates a
small graph and displays it. 

Coloring and re-sizing the nodes using CSS classes works fine, adding labels 
to
the nodes too. 

However, the following CSS code seems to do nothing: 

node {
  text-alignment: under;
  text-background-color: #C0C0C0;
  text-background-mode: rounded-box;
}

I'm adding the labels to the nodes like this: node.addAttribute("ui.label",
"test")

Sadly, there is no error message or exceptions, just nothing changes. 

What could I do to identify the issue here? 

Thank you, 
Emanuel