Android inject js or css to external page webview

webviewclient.java

                //---- Appened STYLE
                //document.getElementsByTagName('html')[0].innerHTML+='<style>*{color:#fff}</style>'
                StringBuilder extraStyles = new StringBuilder();
                extraStyles.append("javascript:(function extra(){");
                if(getResources().getBoolean(R.bool.extraCss)){
                    extraStyles.append(
                            "var aa =document.createElement(\"link\");" +
                                    "aa.type='text/css'; aa.rel='stylesheet'; "+
                                    "aa.href='"+getResources().getString(R.string.extraCssUrl)+"';"+
                            "document.getElementsByTagName(\"head\")[0].appendChild(aa);"
                    );
                }
                if(getResources().getBoolean(R.bool.extraJs)){
                    extraStyles.append(
                            "var bb =document.createElement(\"script\");" +
                            "bb.src='"+getResources().getString(R.string.extraJsUrl)+"';"+
                            "document.getElementsByTagName(\"head\")[0].appendChild(bb);"
                    );
                }
                extraStyles.append("})();");
                Log.d("extraextraStyles",extraStyles.toString());
                browser.loadUrl(extraStyles.toString());