body {
    margin: 0;
    padding: 0;
    background: aqua;
}


#dialogBoxWrap {
    margin: 0;
    background: black;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    opacity: 0.9;
    visibility: hidden;
}

#dialogBoxWrap.visible {
    visibility: visible;
}

#dialogBox {
    background: #9b9b9b;
    width: 300px;
    margin-top: 200px;
    margin-left: auto;
    margin-right: auto;
    padding: 20px;
}