body {
    background-image: url(/static/background.jpg);
    background-size: cover;
}

.overlay-container {
    position: absolute;
    margin: auto;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    max-width: 100%;
    max-height: 100%;
    text-align: center;
    z-index: 1;
    background-color: rgba(255, 255, 255, .1);
}

.overlay-container:before {
    content: '';
    display: inline-block;
    height: 100%;
    vertical-align: middle;
    margin-right: -0.25em;
}

.overlay-content {
    display: inline-block;
    vertical-align: middle;
    padding: 16px;
    text-align: left;
    min-width: 500px;
    max-width: 100%;
    max-height: 100%;
    overflow: auto;
    box-sizing: border-box;
    white-space: nowrap;
    background-color: rgba(255, 255, 255, .9);
}