html {
    font-size: 10px;
    background: url(./images/b9r5sEL.jpg) bottom center;
    background-size: cover;
  }
  body, html {
    margin: 0;
    padding: 0;
    font-family: sans-serif;
  }
  .keys {
    min-height: 100vh;
    /* 弹性布局 */
    /* 键盘， 好多个键/ */
    display: flex;
    align-items: center; /*水平 主轴*/
    justify-content: center; /*垂直 纵轴*/
    /* background-color: red; */
  }
  .key {
    width: 10rem;
    border: .4rem solid black;
    margin: 1rem;
    font-size: 1.5rem;
    padding: 1rem 0.5rem;
    text-align: center;
    color: #ffffff;
    border-radius: .5rem;
    background:rgba(0,0,0,.4);
    text-shadow: 0 0 .5rem black;
    transition: all .07s ease;
  }
  .key > div {
    font-size: 4rem;
  }
  .sound {
    font-size: 1.2rem;
    text-transform: uppercase;
    letter-spacing: .1rem;
    color: #ffc600;
  }
  .playing{
      transform: scale(1.1);
      background-color: #ffc600;
      box-shadow: 0 0 1rem #ffc600;

  }
  
  