/* Alternate by display order in index.html, not by section filename. */
body[data-section-tone="white"] {
    --section-background: #ffffff;
}

body[data-section-tone="gray"] {
    --section-background: #f3f4f6;
}

/* Cover both the iframe canvas and the chapter, including extra-height space.
   Card, icon and image backgrounds remain unchanged. */
body[data-section-tone],
body[data-section-tone] > .section {
    background: var(--section-background);
}