Injecting jQuery into WebBrowser control in WPF application

Question

I have kinda simple problem. The task is to display just part of webpage loaded in WebBrowser control in WPF application. I looked up the problem on stack, but none of the solution helped me nor solved the problem. So what I learned is, that the easiest way to solve this is to inject a javascript/jquery function into the head of loaded page and then call it using WebBrowser.InvokeScript to do DOM manipulation, but whenever I call my function I get script error.

Here are functions that I tried, but none of them worked (I know nothing about jQuery or javascript so I don't really know how to approach the problem):

This one I found on stack (2nd answer here)

function _changeDivs() {
    $('body >').hide(); 
    $('#dex1').show().prependTo('body');
}

I read the jQuery documentation on prepend and prependTo and from what i learned I tried: (here I just tried to get the script to not throw errors)

function _changeDivs() {
    $('body').prepend($('#dex1')); 
}

Simple alert works without problem. Here is code that I use to inject the script:

private void PageLoaded(object sender, NavigationEventArgs e)
{
        var webBrowser = (WebBrowser) sender;

        var doc = (mshtml.HTMLDocument)webBrowser.Document;
        var head = doc.getElementsByTagName("head").Cast<mshtml.HTMLHeadElement>().First();
        var script = (mshtml.IHTMLScriptElement)doc.createElement("script");

        script.text = "function _changeDivs() { $('body >').hide(); $('#dex1').show().prependTo('body'); }";
        head.appendChild((mshtml.IHTMLDOMNode)script);

        webBrowser.InvokeScript("_changeDivs");
 }

In case you'd want to know when PageLoaded is called:

webBrowser.LoadCompleted += PageLoaded;