#overlay{
    z-index:1;

    position:fixed;
    top:0;
    left:0;
    width:100%;
    height:100%;
    background-color:rgba(0,0,0,0.5);

    display: flex;
    align-items: center;
    justify-content: center;
}

#content{
    z-index:2;
    width:80%;
    padding: 1em;
    background:#fff;
}