.btn span{position:relative;z-index:1}.btn-circle{content:"";position:absolute;background-color:#000;opacity:.4;width:0;height:0;left:var(--7fc87785);top:var(--7fc8ebe4);transform:translate(-50%,-50%);border-radius:50%;transition:width .5s,height .5s}.btn:hover .btn-circle{width:350px;height:350px}