style.css

body, html {
    margin: 0;
    padding: 0;
    text-align: left;
}

html {
    width: 100%;
    height: 100%;
}

body {
    width: 100%;
    height: 100%;
    margin: 0;
    background-color: #EEEEEE;
    overflow: hidden;
}

canvas {
    width: 100%;
    height: 100%;
}

.canvas-wrapper {
    height: 74%;
    padding-top: 1%;
    padding-bottom: 1%;
}

.top-area {
    position: relative;
    margin-left: 20%;
    height: 20%;
    overflow-x: scroll;
    overflow-y: hidden;
    margin-right: 20%;
}

.piano-keyboard {
    height: 100%;
    width: 1200px;
    display: inline-block;
}

.piano-key {
    display: inline-block;
    border-bottom-right-radius: 3px;
    border-bottom-left-radius: 3px;
}

.white-key {
    background-color: white;
    width: 40px;
    height: 92%;
    z-index: 5;
    border: solid white 5px;
    margin-left: 2px;
    margin-right: 2px;
}

.black-key {
    background-color: black;
    width: 24px;
    height: 60%;
    position: absolute;
    z-index: 10;
    border: solid black 5px;
    top: 0;
}

.piano-key:hover {
    border: solid #6DF 5px;
}

.playing-key, .playing-key:hover {
    border: solid #48F 5px;
}

.overlay {
    position: absolute;
    bottom: 5px;
    left: 20%;
    right: 20%;
    z-index: 10;
    text-align: center;
    cursor: pointer;
}

.piano-key span {
    color: #999;
    position: absolute;
    bottom: 5%;
}