html, body {
    margin: 0;
    padding: 0;
    height: 100%;
}
body {
    background: url(back.jpg) no-repeat center center fixed;
}
.buttons {
    height: 100%;
    display: flex;
    justify-content: space-around;
    align-items: center;
}
.buttons > button {
    width: 115px;
    border: 4px solid #000;
    background: rgba(0,0,0,0.4);
    transition: all .09s;
}
kbd {
    font-size: 40px;
    color: #fff;
}
.buttons p {
    font-size: 20px;
    color: #eca70e;
}
.playing {
    border-color: #eca70e!important;
    transform: scale(1.2);
    box-shadow: 0 0 10px #eca70e;
}