:root {
  color-scheme: light;
  --navy: #142c48;
  --teal: #087f8c;
  --ink: #27384a;
  --muted: #5d6d7e;
  --line: #dce4ec;
  --paper: #f6f8fc;
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--paper); color: var(--ink); font-family: Arial, Helvetica, sans-serif; line-height: 1.5; }
a { color: var(--teal); text-underline-offset: 3px; }
a:focus-visible { outline: 3px solid #ba7900; outline-offset: 5px; border-radius: 3px; }
.wrap { width: min(1280px, calc(100% - 80px)); margin-inline: auto; }
.skip-link { position: absolute; top: -100px; left: 20px; z-index: 2; padding: 12px 18px; background: white; }
.skip-link:focus { top: 12px; }
.site-header { display: flex; justify-content: space-between; align-items: center; gap: 24px; padding-block: 28px; border-bottom: 1px solid var(--line); }
.school { display: flex; align-items: center; gap: 19px; color: var(--navy); text-decoration: none; }
.school img { width: 72px; height: 72px; }
.school strong { display: block; font-size: 20px; letter-spacing: -.4px; }
.school span span { display: block; margin-top: 3px; font-size: 13px; color: var(--muted); }
.teacher { color: var(--muted); font-size: 15px; }
.intro { display: flex; align-items: center; justify-content: space-between; gap: 48px; padding: 64px 0 56px; }
.eyebrow { margin: 0 0 12px; color: var(--teal); text-transform: uppercase; font-size: 12px; font-weight: 700; letter-spacing: 1.7px; }
h1, h2 { color: var(--navy); letter-spacing: -1.6px; line-height: 1.12; }
h1 { margin: 0 0 20px; font-size: clamp(38px, 4.5vw, 58px); }
.subtitle { max-width: 580px; margin: 0; color: var(--muted); font-size: 18px; line-height: 1.6; }
.course-mark { width: 122px; height: 122px; display: grid; place-items: center; position: relative; flex-shrink: 0; border: 1px solid #c7d6df; border-radius: 24px; background: #eef4f5; transform: rotate(5deg); }
.course-mark span { color: var(--teal); font-weight: 700; font-size: 54px; letter-spacing: -5px; transform: rotate(-5deg); padding-right: 5px; }
.course-mark i { position: absolute; width: 22px; height: 22px; bottom: -5px; right: -5px; border-radius: 50%; background: #f1b544; border: 5px solid var(--paper); }
.chapter { padding-bottom: 45px; }
.chapter-heading { display: flex; justify-content: space-between; align-items: center; gap: 32px; padding: 27px 0 24px; border-top: 3px solid var(--teal); }
.chapter-title .eyebrow { margin-bottom: 8px; font-size: 11px; }
h2 { margin: 0; font-size: clamp(26px, 2.5vw, 34px); letter-spacing: -.8px; }
.chapter-meta { margin: 11px 0 0; color: var(--muted); font-size: 13px; min-height: 20px; }
.actions { display: flex; gap: 12px; flex-wrap: wrap; flex-shrink: 0; }
.button { display: inline-flex; align-items: center; justify-content: center; gap: 10px; min-height: 48px; padding: 12px 17px; border: 1px solid transparent; border-radius: 7px; font-size: 14px; font-weight: 700; text-decoration: none; transition: background-color .15s; }
.button.primary { background: var(--navy); color: white; }
.button.primary:hover { background: #22486e; }
.button.secondary { color: var(--navy); background: white; border-color: #c9d4df; }
.button.secondary:hover { background: #eaf0f6; }
.viewer { overflow: hidden; border: 1px solid #bdcad6; border-radius: 9px; background: #e4e9f0; box-shadow: 0 12px 36px -25px #142c4866; }
.viewer-heading { display: flex; align-items: center; gap: 10px; padding: 14px 20px; color: white; background: var(--navy); font-size: 12px; }
.status-dot { width: 6px; height: 6px; border-radius: 50%; background: #f1b544; }
.file-format { margin-left: auto; color: #c5d4e4; font-size: 10px; letter-spacing: 1px; }
#pdf-viewer { display: block; width: 100%; height: min(78vh, 900px); min-height: 540px; border: 0; }
#pdf-viewer:not([src]) { display: none; }
.mobile-tip { display: none; }
.viewer-fallback { padding: 30px; margin: 0; }
.viewer-help { margin: 14px 0 0; color: var(--muted); font-size: 13px; }
.site-footer { display: flex; justify-content: space-between; gap: 20px; padding-block: 21px 26px; border-top: 1px solid var(--line); color: var(--muted); font-size: 12px; }
.site-footer p { margin: 0; }
.site-footer span { padding-inline: 9px; color: #a2b0bf; }
@media (max-width: 1050px) {
  .chapter-heading { align-items: flex-start; flex-direction: column; gap: 22px; }
}
@media (max-width: 759px) {
  .wrap { width: calc(100% - 40px); }
  .site-header { padding-block: 20px; gap: 18px; align-items: flex-start; }
  .school { gap: 12px; }
  .school img { width: 55px; height: 55px; }
  .school strong { font-size: 17px; }
  .school span span { font-size: 12px; }
  .teacher { display: none; }
  .intro { padding: 41px 0 37px; }
  .course-mark { display: none; }
  .eyebrow { font-size: 11px; letter-spacing: 1.3px; }
  .subtitle { font-size: 16px; }
  .chapter-heading { padding-top: 25px; gap: 23px; }
  .actions { width: 100%; gap: 10px; }
  .button { flex: 1 1 auto; font-size: 13px; padding-inline: 13px; }
  #pdf-viewer { display: none; }
  .mobile-tip { display: block; margin: 0; padding: 25px 22px; font-size: 15px; line-height: 1.7; background: white; }
  .viewer-help { display: none; }
  .site-footer { flex-direction: column; gap: 7px; font-size: 11px; }
}
@media (prefers-reduced-motion: reduce) {
  .button { transition: none; }
}