$(document).ready(function() {

var $sidebar   = $("#sharebox"),
$window    = $(window),
offset     = $sidebar.offset(),
topPadding = 15;

$window.scroll(function() {
if ($window.scrollTop() > offset.top) {
$sidebar.stop().animate({
marginTop: $window.scrollTop() - offset.top + topPadding
});
} else {
$sidebar.stop().animate({
marginTop: 0
});
}
});

});