#site-header{position:fixed;top:0;left:0;width:100%;background-color:#fff;box-shadow:0 2px 8px rgba(0,0,0,.08);z-index:1000;transition:top .3s ease,opacity .25s ease;opacity:1}#site-header.hidden{top:-100px;opacity:0}header:has(>#site-header)+main{margin-top:100px !important}