body {
    background-color: gray;
}

#frame {
    position: relative;
    background-color: #ddd;
    border: 1px solid black;
    margin: auto;
    margin-top: 10px;
    width: 640px;
    height: 480px;
    overflow: hidden;
}

#instructions {
    margin: auto;
    text-align: center;
    padding: 2em;
}

.layer {
    position: absolute;
    margin: 0;
    padding: 0;
    width: 640px;
    height: 480px;
    overflow: hidden;
}

.tile {
    display: block;
    position: absolute;
    width: 256px;
    height: 256px;
}