body{
    height: 100vh;
    margin: 1em;
    overflow: hidden;
}
#viewer > img{
    width: 100%;
    max-width: 100%;
}
#viewer > div{
    background: white;
    height: 75vh;
    width: 75vh;
    max-width: 40vw;
    max-height: 40vw;
}
.border{
    border:1px solid red;
}
.zoombox{
    overflow:hidden;
    height: calc(75vh - 3em);
    max-height: calc(40vw - 3em);
}
#viewer > div{
    position: absolute;
}
#viewer > div > div#text{
    border: 1px solid green;
    padding: 0.5em;
    max-height: 3em;
}