body, html {
    margin: 0;
    padding: 0;
}

* {
    font-family: sans-serif;
}

.fullscreen {
    width: 100vw;
    height: 100vh;
    overflow: hidden;
}

.fullscreen > * {
    width: 100%;
    height: 100%;
}

.overlay {
    position: fixed;
    left: 20px;
    top: 20px;
}

a.back {
    display: block;
    padding: 5px 10px;
    background: #fff;
    border: 1px solid #ccc;
    cursor: pointer;
    text-decoration: none;
    color: #000;
}

a.back:hover {
    background: #ddd;
}