how to place blackground dinamic a button?

how to place blackground dinamic a button?

my code is this:
  1. <!DOCTYPE html>
    <html>
    <head>
      <title>FirstApp</title>
    <script src="lib/jquery.js"></script>
    </head>
    <body>

    <div id="divTest1"></div>
    <script type="text/javascript">
    function createRefreshButton() {
        return $('<button/>', {
            text: 'Refresh Data',
            id: 'btn_refresh',
            click: ClickRefresh
        });
    }
    $('body').append(createRefreshButton())

    function ClickRefresh() {
        alert('refresh');
    }
    </script>
    </body>
    </html>


sorry i am novate and for my english :(