CSS Styling of FocusPanel?

[membersound]

From eg TextBox I know that it is possible to alter the css style of an element by setting the dependentName like this:

textBox.setStyleDependentName("readonly", true);

.gwt-TextBox-readonly {
   background-color: lightgrey;
   border: none;
 }

How can I do the same with FocusPanel?

I tried .gwt-FocusPanel-mystyle but it's not changing anything. Does this work different with focuspanel?

Thanks