inject CSS to a site with webview in android

Question

For example I want to change the background-color of www.google.comto red. I have used webview, and my style.cssfile is i

Answer 1

For Kotlin Users

import this

import android.util.Base64

and this is onPageFinished code

 override fun onPageFinished(view: WebView?, url: String?) {
                injectCSS()
}

and this is the code to call

private fun injectCSS() {
            try {
                val inputStream = assets.open("style.css")
                val buffer = ByteArray(inputStream.available())
                inputStream.read(buffer)
                inputStream.close()
                val encoded = Base64.encodeToString(buffer , Base64.NO_WRAP)
                webframe.loadUrl(
                    "javascript:(function() {" +
                            "var parent = document.getElementsByTagName('head').item(0);" +
                            "var style = document.createElement('style');" +
                            "style.type = 'text/css';" +
                            // Tell the browser to BASE64-decode the string into your script !!!
                            "style.innerHTML = window.atob('" + encoded + "');" +
                            "parent.appendChild(style)" +
                            "})()"
                )
            } catch (e: Exception) {
                e.printStackTrace()
            }

        }