gistfile1.txt

$(document).ready(function () { 
  var top = $('#bookbar').offset().top - parseFloat($('#bookbar').css('margin-top').replace(/auto/, 0));
  $(window).scroll(function (event) {
    // what the y position of the scroll is
    var y = $(this).scrollTop();
  
    // whether that's below the form
    if (y >= top) {
      // if so, ad the fixed class
      $('#bookbar').addClass('fixed');
    } else {
      // otherwise remove it
      $('#bookbar').removeClass('fixed');
    }
  });
});


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CSS: 

#bookbar.fixed {
	position: fixed;
        top: 0px;
}