SharePoint online edit masterpage

Hi,

I want to add JavaScript Code the seattle.master in the sharepoint online

<script src="https://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
<script>
$(document).ready( function() {
    $("#sideNavBox").css("display", "none");
    $("#contentBox").css("margin-left", "20px");
    $("#s4-titlerow").css("display", "none");
    $("#s4-ribbonrow").css("display", "none");
    $("#suiteBarDelta").css("display", "none");
})</script>

I want to add this code to the masterpage via SharePoint Designer 2013. I am able to save the masterpage but the code is neither running nor available in the Developer tools. Is there a Cache problem? If I am downloading the masterpage I can see the changes but they are not running.