styles.css

html{
    height: 100%;
}

body{
    margin: 0;
    padding: 0;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    background-size: cover;
}

.piano{
    display: flex;
    position: relative;
    margin-left: 4px;
    background-color: #00471b;
  width: 750px;
  height: 290px;
  margin: 80px auto;
  padding: 90px 20px 0 50px;
  position: relative;
  border-radius: 10px;
}

.white-key{
    width: 75px;
    height: 250px;
    background-color: #fff;
    border: 4px solid black;
    border-radius: 0 0 4px 4px;
    margin-left: -4px;
    outline: none;
    cursor: pointer;
}

.white-key.active{
    background-color: #c0c0c0;
}

.black-key{
    position: absolute;
    width: 40px;
    height: 150px;
    background-image: linear-gradient(#000000, #303030);
    border: 3px solid black;
    border-radius: 0 0 2px 2px;
    outline: none;
    cursor: pointer;
}

.black-key.active{
    background-image: linear-gradient(#000000, #101010) ;
}

.k9-key{
    left: 100px;
}
.k11-key{
    left: 170px;
}
.k14-key{
    left: 313px;
}
.k16-key{
    left: 385px;
}
.k18-key{
    left: 455px;
}
.k21-key{
    left: 598px;
}
.k23-key{
    left: 668px;
}