How to hide elements of website in Android Webview App?

I'm making a webview app and I want to hide parts of the website like the header and footer I tried to do that by this code

public void onPageFinished(WebView view, String url) {
            view.loadUrl("javascript:(function() { " +
                    "document.getElementsByClassName('header')[0].style.display='none'; })()");
        }

but it only hides it when the page is finished from loading and leave its area blank and don't remove its space

Is there away to hide the class entirely ? If there any tutorials do you recommend in order to do that ?