.book-reader {
    margin-block: 1.5rem;
    overflow: hidden;
    border: 1px solid var(--border-color, #d8dee8);
    border-radius: 12px;
}
.book-reader h3 {
    margin: 0;
    padding: 1rem 1.25rem;
}
.book-reader iframe {
    display: block;
    width: 100%;
    height: 75vh;
    height: 75svh;
    min-height: 400px;
    max-height: 960px;
    border: 0;
    background: #f1f3f5;
}
.book-viewer-help {
    font-size: .9rem;
    line-height: 1.6;
}
@media (max-width: 600px) {
    .book-reader iframe { min-height: 360px; }
}
.book-close {
    margin: 0 1.25rem 1rem;
}
#book-cards button, .book-close {
    font: inherit;
    cursor: pointer;
}
.book-reader {
    scroll-margin-top: 6rem;
}