div#overlay {
    z-index: 2;
    position: fixed;
    background-color: rgba(255, 255, 255, 0.6);
    width: 100vw;
    height: 100vh;
    top: 0;
    bottom: 0;
    overflow: hidden;
}
div#overlay div#overlay-center {
    width: 50vw;
    height: 20vw;
    padding: 2vw;
    border: 1vw solid #999999;
    background-color: #ffffff;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}
div#overlay div.button-box {
    width: 45%;
    height: 3vw;
    display: inline-block;
}
div#overlay button {
    width: 100%;
    height: 3vw;
    font-size: 1.3vw;
    background-color: #66ff66;
    border: .2vw solid #66aa66;
}
div#overlay button:hover {
    cursor: pointer;
}
div#overlay a {
    color: #888888;
    font-size: 1.2vw;
    text-decoration: underline;
    text-align: center;
}