.up--visible{visibility:hidden;z-index:1}.back-to-top{width:50px;height:100vh;position:fixed;left:0;top:0;opacity:0;background:var(--up-bg) url("") 50% 100px no-repeat;visibility:hidden;transition:background 0.4s,opacity 0.3s ease,visibility 0.3s ease;cursor:pointer;background-size:16px 55px}.back-to-top:hover{background-color:var(--up-hover)}.back-to-top--visible{visibility:visible;opacity:1;z-index:999}
.html--air .back-to-top{background:rgb(0 0 0 / .04) url("") 50% center no-repeat}.html--air .back-to-top:hover{background-color:var(--up-hover)}