We need to set the style property of MenuItem label through java class. For the we are taking the MenuItem object through its id and setting the style to the menuitem through .setStyle method of MenuItem.

But its not able to set style to the MenuItem label because style is set to li tag rather than span tag.
Component component = view.getFellowIfAny(fieldId);
MenuItem menuItem = (MenuItem) component;
if (menuItem != null)

Attached the image for detail.