As is this done?

It looks like it's using a bit of jQuery magic.
HTML:
    <script type="text/javascript">
    $(document).ready(function($){

        var backgroundpos = 0;
        var offset = 1;
        function scrollbackground() {
        offset = (offset < 1) ? offset + (backgroundpos - 1) : offset - 1;
          $('.branding').css("background-position",  + offset + "px 0");
          setTimeout(function() {
            scrollbackground();
            }, 100
        );
          }
        scrollbackground();

    });
    </script>
 
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