style.css

html {
    background: url(image.jpg);
    background-size: cover;
    background-repeat: no-repeat;
    background-position: center;
}

body{
    height: 100vh;
    margin: 0;
    padding:0;
    font-family: sans-serif;

}

.keys{
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    text-align: center;
    margin: 0 auto;
    height: 120px;
    margin-top: 225px;

}

.key{
    border: 4px solid rgb(16, 199, 231);
    border-radius: 5px;
    margin: 10px;
    font-size: 15px;
    padding: 10px 40px;
    transition: all 0.07s ease;
    width: 100px;
    color: white;
    background: rgba(0,0,0,0.4);
    text-shadow: 0 0 5px black;
}

kbd{
    display: block;
    font-size: 40px;

}

.sound{
    font-size: 12px;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: #71d81d;
    text-align: center;
}

.playing{
    transform: scale(1.1);
    border-color: rgb(0, 4, 255);
    box-shadow: 0 0 10px rgb(0, 4, 255);

}