How to detect a url change through AJAX without reload in jQuery?

Question

I have a userscript (for Chrome) that I am using to format duolingo's practice pages for me. It just applies a single line of css with

jQ(document).ready(function(){
    jQ('#start-button').css({"float": "left", "margin-right": "10em"});
});

And this works just fine the first time I come to the page. But they use Ajax to avoid page reloads. And the url does change, so if I detect that, I can refresh the css change and not lose the formatting with this site navigation pattern.

Anyone happen to know a good way to detect it?

edit: full user script implementing the popular solution several pointed out at first (which is not working):

// ==UserScript==
// @name         duolingo
// @namespace    http://your.homepage/
// @version      0.1
// @description  reformat /skills to not start timed practice by default
// @author       You
// @include      /^https?\:\/\/www\.duolingo\.com\/(skill|practice)?\/?.*/
// @require      https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js
// @grant        none
// ==/UserScript==

window.jQ=jQuery.noConflict(true);

jQ(document).ready(function(){
    style_duolingo();
});
jQ(window).bind('hashchange', function() {
    style_duolingo();
});
jQ(document).ajaxComplete(function() {
    style_duolingo();
});


function style_duolingo() {
    jQ('#start-button').css({"float": "left", "margin-right": "10em"});
    console.log("Tampermonkey script: wrote css change");
}

edit #2:

For bounty reward

Please provide a working solution that does not load external libraries (I'd like to know what I am missing, not keep it in a black box), and solves the issue using events (no interval-based solution). If events (bizarrely) cannot be used, please provide the correction solution and the reason why events are not being triggered.

Answer 1

To change the url Duolingo uses history.pushstate. I recommend you galambalazs answer to similar question

This is his code:

(function(history){
    var pushState = history.pushState;
    history.pushState = function(state) {
    if (typeof history.onpushstate == "function") {
        history.onpushstate({state: state});
    }

    //Custom code here
    style_duolingo();

    return pushState.apply(history, arguments);
}
})(window.history);