Resizing margins based on window size

gistfile1.js

$('.home_details').css("margin-top", function(){
  if ($(window).height() > 642) {
		return "0px";
	} else {
		return (((642 - $(window).height())) / 6.8) + "px";
		console.log(737 - ($(window).height()) + "px");
	}
});