The demo is keeping the element’s position:fixed
and manipulating the left
property of the element:
var leftInit = $(".scroll_fixed").offset().left;
var top = $('.scroll_fixed').offset().top - parseFloat($('.scroll_fixed').css('margin-top').replace(/auto/, 0));
$(window).scroll(function(event) {
var x = 0 - $(this).scrollLeft();
var y = $(this).scrollTop();
// whether that's below the form
if (y >= top) {
// if so, ad the fixed class
$('.scroll_fixed').addClass('fixed');
} else {
// otherwise remove it
$('.scroll_fixed').removeClass('fixed');
}
$(".scroll_fixed").offset({
left: x + leftInit
});
});
Using leftInit
takes a possible left margin into account. Try it out here: http://jsfiddle.net/F7Bme/