How to change Background image in sap.m.Page control

I am new to SAPUI5. I want to change the background image within sap.m.Page control but unable to do that. Please suggest how to do that. Trying with the following way:

var myTripPage = new sap.m.Page({

                            customHeader:titleBar,

                            content: [

                                      oFlexBox

                                     ],

                           footer : new sap.m.Bar({

                                          contentMiddle: new sap.m.Button({

                                                                      text :"Submit"

                                                                       })

                                                  })

                                });

              myTripPage.addStyleClass('mystyle');