How do we change the font size of text present in Application Header control

Hi,

I created an Application header control of SAPUI5 in eclipse but the text in that is small..Can't we change the size of the text?

This is my Code

var oAppHeader = new sap.ui.commons.ApplicationHeader("appHeader");

        //configure the branding area

        oAppHeader.setLogoSrc("http://www.sap.com/global/images/SAPLogo.gif");

        oAppHeader.setLogoText("Proof Of Concept");

        //configure the welcome area

        oAppHeader.setDisplayWelcome(true);

        oAppHeader.setUserName("Sindhuja");

        //configure the log off area

        oAppHeader.setDisplayLogoff(true);

and also I want to know the coding for Log Off if we click on Log Off button.

Please help me