<header id="hd"></header>
<section class="wrap"></section>
<div id="startAni">
<style>
#hd {
position: fixed;
left: 0;
right: 0;
top: 0;
height: 80px;
background-color: black;
z-index: 1000;
transition: 0.5s;
}
#hd.up {
transform: translateY(-100%);
}
.wrap {
height: 5000px;
}
#startAni {
height: calc(100vh + 50px);
transition: 0.5s;
}
#startAni.color {
background-color: rgb(81, 127, 255);
}
</style>
<script>
$(document).ready(function () {
var didScroll;
var lastScrollTop = 0;
var delta = 5;
var navbarHeight = $('#hd').outerHeight();
$(window).on('scroll', function (event) {
didScroll = true;
if ($(this).scrollTop() > $('#startAni').offset().top) {
$('#startAni').addClass('color');
}
});
setInterval(function () {
if (didScroll) {
hasScrolled();
didScroll = false;
}
}, 250);
function hasScrolled() {
var st = $(this).scrollTop();
if (Math.abs(lastScrollTop - st) <= delta) return;
if (st > lastScrollTop && st > navbarHeight) {
$('#hd').addClass('up');
}
else {
$('#hd').removeClass('up');
}
lastScrollTop = st;
}
})
</script>