#demo{height:28vw;margin:6vw;position:relative}#demo .key{background-color:#fff;border:2px solid gray;border-radius:1vw;color:#000;position:absolute;transition-duration:.25s;transition-property:color,background-color;transition-timing-function:ease-in-out}#demo .key.active{background-color:#000;color:#fff}