//菜单固定随滚动条滑动
function navscroll(id){
var $sidebar = $(id),
$window = $(window),
offset = $sidebar.offset(),
topPadding = 0;
$window.scroll(function() {
if ($window.scrollTop() > offset.top) {
$sidebar.stop().animate({
marginTop: $window.scrollTop() - offset.top + topPadding
});
} else {
$sidebar.stop().animate({
marginTop: 0
});
}
});
}