stylee.css

html{
    font-size: 10px;
    background: url(background.jpg) bottom center;
    background-size: cover;
}
body,html{
    margin: 0px;
    padding: 0px;
}

.keys{
    display: flex;
    flex: 1;
    height: 100vh;
    align-items: center;
    justify-content: center;
}

.key{
    border: .4rem solid black;
    border-radius: .5rem;
    margin:1rem;
    width:10rem;
    color: white;
    background:rgba(0,0,0,0.4);
    text-shadow: 0 0 0.5rem black;
    font-size: 1.5rem;
    padding: 1rem 0.5rem;
    transition: all 70ms ease;
    text-align: center;
}

.playing{
    transform: scale(1.1);
    border-color:#ffc600;
    box-shadow: 0 0 1rem #ffc600;
}

kbd{
    display: block;
    font-size: 4rem;
}

.sound{
    font-size:1.2rem;
    letter-spacing:.1rem;
    color: #ffc600;
    text-transform: uppercase;
    font-family: sans-serif;
}