Header changes as you scroll down (jQuery)

Question

TechCrunch recently redesigned their site and they have a sweet header that minifies into a thinner version of their branding as you scroll down.

You can see what I

Answer 1

$(window).on("scroll", function () {
    if ($(this).scrollTop() > 100) {
        $("#header").addClass("not-transparent");
    }
    else {
        $("#header").removeClass("not-transparent");
    }
});