wv.loadUrl("<style>.featured {"+
        "   background-image: -ms-linear-gradient(bottom, #F9F6F9 0%, #ECE4F4 100%);"+
        "   background-image: -moz-linear-gradient(bottom, #F9F6F9 0%, #ECE4F4 100%);"+
        "   background-image: -o-linear-gradient(bottom, #F9F6F9 0%, #ECE4F4 100%);"+
        "background-image: -webkit-gradient(linear, left bottom, left top, color-stop(0, #F9F6F9), color-stop(1, #ECE4F4));"+
        "   background-image: -webkit-linear-gradient(bottom, #F9F6F9 0%, #ECE4F4 100%);"+
        "   background-image: linear-gradient(to top, #F9F6F9 0%, #ECE4F4 100%);"+
        "}");

WebView webview = (WebView) findViewById(R.id.abtus_webView);
webview.loadUrl("file:///android_asset/index.html");

<img src="file:///android_asset/images/abc.png">

wv.loadUrl("javascript:(function() { " +
    "var divs = document.getElementsByClassName('free');"+
     "for(var i=0; i<divs.length; i++)"+
     "{"+
        "divs[i].style.backgroundImage='-webkit-gradient(linear, left bottom, left top, color-stop(0, #FFFFFF), color-stop(1, #EFD2E4))';"+
      "}"+
     "})()");