how to apply css in gwt to all screens dynamically at a time

I have created UI Screens using GWT for some application. i want to al开发者_如何学Pythonlow the user to change the color for buttons, text and under line and background-colors. Here what i want to do is to apply a single CSS for colors it will reflect in all the screens dynamically.

   How to do this? can anyone please help me.

Thanks and Regards, G Ravi Kumar

Each GWT widget has the methods "addStyleName" and "removeStyleName", e.g. this Button:

    Button b = new Button();
    b.addStyleName("helloworld");
    b.removeStyleName("helloworld");