body {
  font-family: 'Open Sans', sans-serif;
  background: #303030;
}
figure.keyboard {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 370px;
  -webkit-transform-origin: center center;
  transform-origin: center center;
  -webkit-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
}
[data-key] {
  position: relative;
  display: block;
  float: left;
  color: #eee;
  border: 1px solid #eee;
  border-radius: 3px;
  width: 25px;
  line-height: 25px;
  text-align: center;
  font-style: normal;
  padding: 3px;
  margin: 2px;
  cursor: pointer;
  transition: all .2s;
  
  &[data-key="A"] {
    clear: left;
    margin-left: 10px;
  }
  &[data-key="Z"] {
    clear: left;
    margin-left: 28px;
  }
  &:after {
    content: attr(data-note) ' Hz';
    position: absolute;
    width: 100%;
    top: 0;
    left: 0;
    font-size: 10px;
    line-height: 10px;
    padding-top: 4px;
    color: #303030;
    opacity: 0;
  }
  
  &:hover,
  &:focus,
  &.active {
    background: #eee;
    
    &:after {
      opacity: 1;
    }
  }
}