MediaWiki:Common.css

display: inline-block; height: 40px; width: 40px; position: fixed; bottom: 40px; right: 10px; border-radius: 20px; box-shadow: rgba(0, 0, 0, 0.05) 0px 0px 10px; z-index: 99; overflow: hidden; text-indent: 100%; white-space: nowrap; opacity: 0.5; background: url(https://raw.githubusercontent.com/Bhpsngum/img-src/master/arrow-top.svg) center 50% no-repeat rgba(120, 172, 245, 0.8); }
 * 1) backtotop {

opacity: 1; }
 * 1) backtotop:hover {