I am trying to add a printer icon to the header section of a ContentPanel. I defined a style (x-tool-printerIcon with my custom background image) I am trying to add it to the header using the following code:

 contentPanelInstance.getHeader().addTool(new ToolButton("x-tool-printIcon"));
I am unable to see it on the header. I am, however able to trace the correct style using browser's developer toolbar. What am I missing ?