body {
    background: cornflowerblue;
}
#slideshow {
    width: 300px;
    height: 600px;
    position: relative;
    overflow: hidden;
}

#preview {
    position: absolute;
}

ol {
    list-style: none;
    margin: 0;
    padding: 0;
}

main a {
    display: block;
    width: 400px;
    line-height: 48px;
    font-size: 24px;
    text-decoration: none;
    border: 4px solid cornflowerblue;
    border-radius: 12px;
    background: blue;
    color: white;
    text-align: center;
}