This is jquery code which is used to fixed the div when it touch a top of browser hope it will help a lot.
<script type='text/javascript' src='http://code.jquery.com/jquery-1.7.1.js'></script>
<script type='text/javascript'>//<![CDATA[
$(window).load(function(){
$(function() {
$.fn.scrollBottom = function() {
return $(document).height() - this.scrollTop() - this.height();
};
var $el = $('#sidebar>div');
var $window = $(window);
var top = $el.parent().position().top;
$window.bind("scroll resize", function() {
var gap = $window.height() - $el.height() - 10;
var visibleFoot = 172 - $window.scrollBottom();
var scrollTop = $window.scrollTop()
if (scrollTop < top + 10) {
$el.css({
top: (top - scrollTop) + "px",
bottom: "auto"
});
} else if (visibleFoot > gap) {
$el.css({
top: "auto",
bottom: visibleFoot + "px"
});
} else {
$el.css({
top: 0,
bottom: "auto"
});
}
}).scroll();
});
});//]]>
</script>