#to-top{position:fixed;right:16px;bottom:16px;z-index:9999;width:44px;height:44px;border-radius:50%;
background:#111;color:#fff;border:0;cursor:pointer;display:none;align-items:center;justify-content:center;
box-shadow:0 8px 24px rgba(10,20,40,.25)}
#to-top.visible{display:flex}
#to-top:after{content:"▲";font-size:16px;line-height:1}