Customise Look not working in IOS SDK Integration

Hi I tried integrating the iOS SDK. While following the guide "Customise The Look", I did not find any other fields other than primary color to change. I tried adding a new help_center css file and that too doesn't seem to work. Could you please suggest any other ways to change the color of the header.
 

I have also attached the image and the code snippet.

let hcConfig = HelpCenterUiConfiguration()

hcConfig.labels = ["mobile article"]

let helpCenter = HelpCenterUi.buildHelpCenterOverviewUi(withConfigs: [hcConfig])

CommonTheme.currentTheme.primaryColor = UIColor.blue

self.navigationController?.pushViewController(helpCenter, animated: true)