:root {
  color-scheme: light;
  --text: #111;
  --muted: #444;
  --line: #6b6b6b;
  --light-line: #c8c8c8;
  --paper: #fff;
  --soft: #f4f4f2;
  --font-scale: 1;
}

* { box-sizing: border-box; }

html {
  background: var(--paper);
  color: var(--text);
  font-family: Arial, "Noto Sans TC", "Microsoft JhengHei", sans-serif;
  scroll-behavior: auto;
}

body {
  margin: 0;
  background: var(--paper);
  font-size: calc(clamp(20px, 1.35vw, 25px) * var(--font-scale));
  line-height: 1.78;
}

body[data-font-size="large"] { --font-scale: 1.18; }

a { color: #111; text-decoration-thickness: 0.08em; text-underline-offset: 0.15em; }
a:hover { text-decoration-thickness: 0.14em; }

:focus-visible {
  outline: 3px solid #111;
  outline-offset: 4px;
}

.skip-link {
  position: absolute;
  left: 1rem;
  top: -10rem;
  padding: 0.5rem 0.8rem;
  background: #fff;
  border: 2px solid #111;
  z-index: 10;
}

.skip-link:focus { top: 1rem; }

.site-header,
.site-footer,
.page-shell {
  width: min(1180px, calc(100% - 2.5rem));
  margin-inline: auto;
}

.site-header {
  padding: 1.5rem 0 1rem;
  border-bottom: 2px solid var(--text);
}

.institution {
  margin: 0;
  color: var(--muted);
  font-size: 1em;
  letter-spacing: 0.03em;
}

.course-name {
  margin: 0.15rem 0 0;
  font-weight: 700;
  font-size: 1.15em;
}

.utility-nav,
.unit-nav,
.page-controls,
.form-actions,
.prompt-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem 1rem;
  align-items: center;
}

.utility-nav { margin-top: 0.8rem; font-size: 1em; }

button,
.button-link {
  appearance: none;
  display: inline-flex;
  min-height: 44px;
  align-items: center;
  justify-content: center;
  border: 1.5px solid #111;
  border-radius: 0;
  background: #fff;
  color: #111;
  font: inherit;
  font-size: 1em;
  line-height: 1.25;
  padding: 0.52rem 0.8rem;
  cursor: pointer;
  text-decoration: none;
}

button:hover,
.button-link:hover { background: var(--soft); }

.page-shell { padding: 1.6rem 0 3.5rem; }

.course-position {
  margin: 0 0 0.4rem;
  font-size: 1em;
  color: var(--muted);
  letter-spacing: 0.04em;
}

h1, h2, h3 {
  line-height: 1.28;
  text-wrap: balance;
}

h1 { margin: 0.2rem 0 0.8rem; font-size: clamp(2rem, 4vw, 3.05rem); }
h2 { margin: 0 0 0.7rem; font-size: 1.62em; }
h3 { margin: 1.2rem 0 0.45rem; font-size: 1.28em; }

p { margin: 0.65rem 0; max-width: 74ch; }
li + li { margin-top: 0.35rem; }

.subtitle { margin: 0 0 1.2rem; font-size: 1.1em; color: var(--muted); }

.unit-meta {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0;
  margin: 1.4rem 0;
  border-block: 1px solid var(--line);
}

.unit-meta div { padding: 0.8rem 1rem; border-right: 1px solid var(--light-line); }
.unit-meta div:last-child { border-right: 0; }
.unit-meta dt { font-size: 1em; color: var(--muted); }
.unit-meta dd { margin: 0.15rem 0 0; font-weight: 700; }

section {
  padding: 1.6rem 0 0.7rem;
  border-top: 1px solid var(--light-line);
}

section:first-of-type { border-top: 2px solid var(--text); }

.lead {
  max-width: 70ch;
  font-family: Georgia, "Noto Serif TC", "PMingLiU", serif;
  font-size: 1.12em;
  line-height: 1.8;
}

blockquote {
  margin: 1.2rem 0;
  padding: 0.2rem 0 0.2rem 1.2rem;
  border-left: 4px solid #111;
  font-family: Georgia, "Noto Serif TC", "PMingLiU", serif;
}

.note,
.warning,
.exercise-intro {
  max-width: 74ch;
  padding: 0.75rem 1rem;
  border-left: 4px solid #333;
  background: var(--soft);
}

.warning { border-left-style: double; border-left-width: 7px; }

.viewer-layout {
  display: grid;
  grid-template-columns: minmax(0, 1.1fr) minmax(0, 0.9fr);
  gap: 1.2rem;
  align-items: start;
}

.viewer-panel {
  min-width: 0;
  padding: 1rem;
  border: 1px solid var(--line);
}

.viewer-panel h2,
.viewer-panel h3 { margin-top: 0; }

.viewer-context {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.8rem;
  margin: 1rem 0;
}

.viewer-context div {
  padding: 0.8rem;
  border: 1px solid var(--light-line);
  background: var(--soft);
}

.viewer-context dt { color: var(--muted); }
.viewer-context dd { margin: 0.2rem 0 0; font-weight: 700; }

.viewer-prompt {
  min-height: 24rem;
  max-height: 52rem;
  overflow: auto;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
}

.viewer-checks { margin: 0 0 1rem; }
.viewer-checks label { display: block; margin: 0.5rem 0; }
.viewer-checks input { margin-right: 0.5rem; }

.viewer-instruction {
  padding: 0.8rem 1rem;
  border-left: 4px solid #333;
  background: var(--soft);
}

.table-wrap {
  overflow-x: auto;
  margin: 1rem 0 1.4rem;
  border: 1px solid var(--line);
}

.table-hint { margin: 0 0 0.4rem; font-size: 1em; color: var(--muted); }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 1em;
  line-height: 1.5;
}

caption {
  text-align: left;
  font-weight: 700;
  padding: 0.7rem;
  border-bottom: 1px solid var(--line);
}

th, td {
  min-width: 8.5rem;
  padding: 0.72rem;
  vertical-align: top;
  text-align: left;
  border: 1px solid var(--light-line);
}

th { background: var(--soft); font-weight: 700; }

pre,
textarea.prompt-text {
  width: 100%;
  margin: 0.7rem 0;
  border: 1px solid var(--line);
  background: #fff;
  color: #111;
  font-family: "Cascadia Mono", Consolas, monospace;
  font-size: 1em;
  line-height: 1.55;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
  tab-size: 2;
}

pre { padding: 1rem; overflow: auto; }
textarea.prompt-text { min-height: 22rem; padding: 1rem; resize: vertical; }

form[data-workbook] {
  max-width: 900px;
  margin: 1rem 0;
}

fieldset {
  margin: 0 0 1.2rem;
  padding: 1rem;
  border: 1px solid var(--line);
}

legend { padding: 0 0.4rem; font-weight: 700; }

.field { margin: 0 0 1rem; }
.field label { display: block; margin-bottom: 0.3rem; font-weight: 700; }
.field .help { display: block; margin: 0 0 0.35rem; color: var(--muted); font-size: 1em; }

input[type="text"],
input[type="number"],
select,
textarea:not(.prompt-text) {
  width: 100%;
  min-height: 50px;
  padding: 0.55rem 0.65rem;
  border: 1.5px solid #555;
  border-radius: 0;
  background: #fff;
  color: #111;
  font: inherit;
  font-size: 1em;
}

textarea:not(.prompt-text) { min-height: 7rem; resize: vertical; }

.check-list label {
  display: grid;
  grid-template-columns: 1.4rem 1fr;
  gap: 0.55rem;
  align-items: start;
  margin: 0.45rem 0;
}

input[type="checkbox"], input[type="radio"] { width: 1.15rem; height: 1.15rem; margin-top: 0.35rem; }

.storage-note,
.status,
.source-note,
.download-meta {
  font-size: 1em;
  color: var(--muted);
}

.downloads-list { padding-left: 1.2rem; }
.downloads-list li { margin-bottom: 0.7rem; }

.course-map {
  padding: 1rem 0;
  border-block: 1px solid var(--line);
}

.course-map ol {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.4rem 1.5rem;
  margin: 0;
  padding-left: 1.4rem;
  font-size: 1em;
}

.course-map li { min-width: 0; line-height: 1.45; }
.course-map a { display: inline; }

.course-map a[aria-current="page"] { font-weight: 700; text-decoration-thickness: 0.16em; }

.transition {
  margin-top: 1.6rem;
  padding: 1.2rem 0;
  border-block: 2px solid #111;
}

.unit-nav { margin-top: 1.3rem; justify-content: space-between; }

.site-footer {
  padding: 1.2rem 0 2rem;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 1em;
}

.print-chapter { break-before: page; }

@media (max-width: 800px) {
  .site-header, .site-footer, .page-shell { width: min(100% - 1.3rem, 1180px); }
  .unit-meta { grid-template-columns: 1fr 1fr; }
  .unit-meta div:nth-child(2) { border-right: 0; }
  .unit-meta div:nth-child(-n+2) { border-bottom: 1px solid var(--light-line); }
  .course-map ol { display: block; }
  .course-map li + li { margin-top: 0.25rem; }
  .unit-nav { align-items: stretch; }
  .unit-nav .button-link { flex: 1 1 100%; }
  .viewer-layout,
  .viewer-context { grid-template-columns: 1fr; }
}

@media (max-width: 430px) {
  body { font-size: 20px; }
  .unit-meta { grid-template-columns: 1fr; }
  .unit-meta div { border-right: 0; border-bottom: 1px solid var(--light-line); }
  .unit-meta div:last-child { border-bottom: 0; }
  h1 { font-size: 2rem; }
}

@media print {
  @page { size: A4; margin: 18mm; }
  html, body { font-size: 12pt; line-height: 1.55; }
  .site-header, .site-footer, .page-controls, .course-map, .unit-nav,
  .prompt-actions, .form-actions, .storage-note, .table-hint, .skip-link { display: none !important; }
  .page-shell { width: 100%; padding: 0; }
  h1 { font-size: 24pt; }
  h2 { font-size: 18pt; }
  h3 { font-size: 14pt; }
  h4 { font-size: 12pt; }
  h1, h2, h3, h4 { break-after: avoid-page; }
  p, li { orphans: 3; widows: 3; }
  table { width: 100%; table-layout: fixed; font-size: 7.5pt; line-height: 1.3; }
  thead { display: table-header-group; }
  tr, blockquote, fieldset { break-inside: avoid; }
  .table-wrap { overflow: visible; border: 0; }
  th, td { min-width: 0; padding: 1.5mm; overflow-wrap: anywhere; }
  a { color: #000; }
  textarea.prompt-text { display: none; }
  .prompt-print {
    display: block;
    margin: 0.7rem 0;
    padding: 3mm;
    border: 1px solid #555;
    font-family: "Cascadia Mono", Consolas, monospace;
    font-size: 9pt;
    line-height: 1.45;
    white-space: pre-wrap;
    overflow-wrap: anywhere;
    break-inside: auto;
  }
  section { break-inside: auto; }
  .print-chapter { break-before: page; }
  .print-chapter:first-child { break-before: auto; }
}