https://www.kyotoanimation.co.jp/kotenbu/TVアニメ「氷菓」京アニサイト | 京都アニメーションDownload
Cuckoo/includes/header.php body
<div id="siteWrap"></div>
<script src="https://shiraikuroko.com/usr/themes/Cuckoo/assets/js/jquery.min.js"></script>
<script src="https://shiraikuroko.com/usr/themes/Cuckoo/assets/js/snowfall.jquery.kotenbu.js"></script>
<script src="https://shiraikuroko.com/usr/themes/Cuckoo/assets/js/kotenbuIndex.js"></script>
更多css：

#siteWrap {
position: fixed;
width: 100%;
min-height: 100vh;
pointer-events: none;
z-index: 1;
}