/**
 * 教材级讲义 · 屏幕阅读 + A4 打印
 */
:root {
  --tb-accent: #0f766e;
  --tb-accent-2: #0d9488;
  --tb-ink: #1e293b;
  --tb-soft: #475569;
  --tb-line: #cbd5e1;
  --tb-paper: #fffdf8;
  --tb-card: #f0fdfa;
  --tb-warn: #9a3412;
  --tb-ok: #166534;
}

body.textbook-page {
  margin: 0;
  min-height: 100dvh;
  font-family: "Source Han Serif SC", "Noto Serif SC", "Songti SC", "SimSun", "Georgia", serif;
  background:
    radial-gradient(circle at 10% 0%, rgba(204, 251, 241, 0.55), transparent 42%),
    linear-gradient(165deg, #e0f2fe 0%, #f0fdfa 46%, #e2e8f0 100%);
  color: var(--tb-ink);
  padding: 0 1rem 2.5rem;
}

.tb-wrap {
  max-width: 900px;
  margin: 0 auto;
}

.tb-top {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.5rem;
  align-items: center;
  margin: 0.7rem auto 0.55rem;
  padding: 0.55rem 0.85rem;
  background: #fff;
  border: 3px solid #134e4a;
  border-radius: 14px;
  position: sticky;
  top: 0;
  z-index: 30;
}

.tb-top strong {
  color: var(--tb-accent);
  font-size: 1.05rem;
}

.tb-top a {
  color: var(--tb-accent);
  font-weight: 800;
  text-decoration: none;
  border: 2px solid var(--tb-accent-2);
  border-radius: 999px;
  padding: 0.28rem 0.75rem;
  background: #f0fdfa;
}

.tb-panel {
  background: #fff;
  border: 2px solid rgba(15, 118, 110, 0.28);
  border-radius: 14px;
  padding: 0.85rem 1rem;
  margin: 0.55rem 0;
  box-shadow: 0 8px 24px rgba(15, 23, 42, 0.06);
}

.tb-panel h3 {
  margin: 0 0 0.45rem;
  font-size: 0.95rem;
  color: var(--tb-accent);
}

.tb-checks {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem 0.85rem;
  font-size: 0.86rem;
  font-weight: 700;
  color: var(--tb-soft);
}

.tb-checks label {
  display: inline-flex;
  align-items: center;
  gap: 0.32rem;
  cursor: pointer;
}

.tb-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  margin-top: 0.65rem;
}

.tb-btn {
  font-family: inherit;
  font-weight: 800;
  border: 3px solid var(--tb-accent);
  background: linear-gradient(180deg, #fff, #f0fdfa);
  color: var(--tb-accent);
  border-radius: 999px;
  padding: 0.42rem 0.95rem;
  cursor: pointer;
}

.tb-btn.primary {
  background: var(--tb-accent);
  color: #fff;
}

.tb-hint {
  font-size: 0.8rem;
  color: #0f766e;
  font-weight: 700;
  text-align: center;
  margin: 0.4rem 0;
}

main.sheet.tb-sheet {
  background: var(--tb-paper);
  border: 4px solid var(--tb-accent-2);
  border-radius: 16px 28px 16px 20px;
  padding: 1.25rem 1.35rem 2rem;
  box-shadow: 8px 12px 0 rgba(13, 148, 136, 0.12);
}

.tb-cover {
  text-align: center;
  padding: 1rem 0.75rem 1.1rem;
  margin-bottom: 1rem;
  border-radius: 16px;
  background: linear-gradient(145deg, #115e59, #134e4a 62%, #0f172a);
  color: #ecfdf5;
}

.tb-cover .kicker {
  letter-spacing: 0.12em;
  font-size: 0.78rem;
  font-weight: 800;
  opacity: 0.9;
}

.tb-cover h1 {
  margin: 0.25rem 0 0.35rem;
  font-size: clamp(1.35rem, 3vw, 1.8rem);
}

.tb-cover p {
  margin: 0 auto;
  max-width: 38em;
  font-size: 0.92rem;
  line-height: 1.55;
}

.tb-meta {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.6rem;
  margin: 0.85rem 0 1rem;
  font-size: 0.9rem;
}

.tb-meta .field label {
  display: block;
  font-weight: 800;
  color: var(--tb-soft);
  margin-bottom: 0.2rem;
}

.tb-meta .line {
  border-bottom: 2px solid #1e293b;
  min-height: 1.45rem;
}

.tb-page {
  break-inside: avoid;
  page-break-inside: avoid;
  margin: 1.15rem 0 1.4rem;
  padding-top: 0.2rem;
}

.tb-page-head {
  display: flex;
  align-items: baseline;
  gap: 0.55rem;
  border-bottom: 3px solid rgba(15, 118, 110, 0.35);
  margin-bottom: 0.7rem;
  padding-bottom: 0.25rem;
}

.tb-tag {
  font-size: 0.75rem;
  font-weight: 900;
  color: #fff;
  background: var(--tb-accent);
  border-radius: 999px;
  padding: 0.12rem 0.55rem;
}

.tb-page-head h2 {
  margin: 0;
  font-size: 1.12rem;
  color: var(--tb-accent);
}

.tb-block {
  margin: 0.7rem 0;
}

.tb-block h3 {
  margin: 0 0 0.4rem;
  font-size: 1rem;
  color: #0f172a;
}

.tb-def,
.tb-formula,
.tb-note,
.tb-example,
.tb-pitfall {
  border-radius: 12px;
  padding: 0.7rem 0.85rem;
  margin: 0.4rem 0;
  border: 1px solid var(--tb-line);
}

.tb-def {
  background: #f0fdfa;
  border-left: 5px solid var(--tb-accent-2);
}

.tb-formula {
  text-align: center;
  font-weight: 900;
  font-size: 1.05rem;
  background: linear-gradient(180deg, #ecfeff, #fff);
  border: 2px solid var(--tb-accent-2);
  line-height: 1.45;
}

.tb-formula-stack {
  text-align: left;
  display: flex;
  flex-direction: column;
  align-items: stretch;
  gap: 0.28rem;
}

.tb-formula-line {
  display: block;
  text-align: left;
  line-height: 1.5;
}

.tb-key ol,
.tb-key ul {
  margin: 0.2rem 0 0;
  padding-left: 1.2rem;
}

.tb-key li {
  margin: 0.28rem 0;
  line-height: 1.55;
}

.tb-example {
  background: #fff;
}

.tb-example .en {
  font-weight: 800;
  color: #0f172a;
}

.tb-example .zh {
  color: var(--tb-soft);
  margin-top: 0.15rem;
}

.tb-example .note {
  margin-top: 0.3rem;
  font-size: 0.88rem;
  color: #0f766e;
  font-weight: 700;
}

.tb-lecture-flow {
  overflow: hidden;
}

.tb-lecture-flow::after {
  content: "";
  display: block;
  clear: both;
}

.tb-lecture-flow > .tb-fig {
  float: right;
  width: min(38%, 240px);
  margin: 0 0 0.85rem 1.1rem;
  position: relative;
  z-index: 1;
  background: var(--tb-paper);
}

.tb-fig {
  margin: 0;
}

.tb-fig img {
  width: 100%;
  max-height: 280px;
  object-fit: contain;
  object-position: top center;
  border-radius: 12px;
  border: 2px solid rgba(15, 118, 110, 0.2);
  display: block;
  background: #fff;
}

.tb-fig figcaption {
  font-size: 0.78rem;
  color: var(--tb-soft);
  text-align: center;
  margin-top: 0.3rem;
}

.tb-lecture-flow table.tb-table {
  clear: both;
}

table.tb-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.88rem;
  margin: 0.35rem 0;
}

.tb-table th,
.tb-table td {
  border: 1px solid #d7e3ea;
  padding: 0.38rem 0.5rem;
  text-align: left;
  vertical-align: top;
}

.tb-table th {
  background: #0f766e;
  color: #fff;
}

.tb-table tr:nth-child(even) td {
  background: #f0fdfa;
}

.tb-pitfall {
  background: #fff7ed;
  border-color: #fdba74;
}

.tb-pitfall .wrong {
  color: var(--tb-warn);
  font-weight: 800;
}

.tb-pitfall .right {
  color: var(--tb-ok);
  font-weight: 800;
}

.tb-q {
  margin: 0.55rem 0;
  padding: 0.55rem 0.65rem 0.65rem;
  border-radius: 12px;
  background: #fff;
  border: 1px solid #e2e8f0;
}

.tb-lead {
  font-size: 0.88rem;
  font-weight: 700;
  color: var(--tb-soft);
  margin-bottom: 0.3rem;
}

.tb-q .num {
  font-weight: 900;
  color: var(--tb-accent);
  margin-right: 0.25rem;
}

.tb-options {
  margin: 0.3rem 0 0.15rem;
  padding-left: 1.4rem;
}

.tb-options li {
  margin: 0.12rem 0;
}

.tb-blank {
  display: inline-block;
  min-width: 4.2em;
  border-bottom: 2px solid #1e293b;
  height: 1.05em;
  vertical-align: baseline;
  margin: 0 0.12em;
}

.tb-match {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.5rem 1rem;
  margin-top: 0.35rem;
}

.tb-answer {
  display: none;
  margin-top: 0.35rem;
  padding: 0.4rem 0.55rem;
  border-radius: 8px;
  background: #ecfdf5;
  color: #14532d;
  font-size: 0.86rem;
  font-weight: 700;
}

body.show-answers .tb-answer {
  display: block;
}

.tb-tier {
  font-size: 0.75rem;
  font-weight: 900;
  border-radius: 6px;
  padding: 0.08rem 0.4rem;
  background: #ccfbf1;
  color: #115e59;
  margin-right: 0.3rem;
}

.tb-missing {
  padding: 0.8rem;
  border: 2px dashed #94a3b8;
  color: #64748b;
  border-radius: 12px;
}

.tb-test-head {
  display: flex;
  justify-content: space-between;
  gap: 0.5rem;
  align-items: baseline;
  margin: 0.4rem 0 0.7rem;
}

.print-off {
  opacity: 0.38;
  outline: 2px dashed #94a3b8;
}

.tb-section {
  margin: 1.2rem 0 1.5rem;
}

.tb-section > h2 {
  font-size: 1.2rem;
  color: var(--tb-accent);
  margin: 0 0 0.45rem;
}

@media screen and (max-width: 720px) {
  .tb-match,
  .tb-meta {
    grid-template-columns: 1fr;
  }
  .tb-lecture-flow > .tb-fig {
    float: none;
    width: min(100%, 320px);
    margin: 0 auto 0.75rem;
  }
}

@media print {
  @page {
    size: A4 portrait;
    margin: 16mm 14mm 16mm 14mm;
  }
  html,
  body.textbook-page {
    background: #fff !important;
    padding: 0;
    -webkit-print-color-adjust: exact;
    print-color-adjust: exact;
  }
  .no-print,
  .tb-top,
  .tb-panel,
  .tb-hint {
    display: none !important;
  }
  main.sheet.tb-sheet {
    border: 0;
    box-shadow: none;
    border-radius: 0;
    padding: 0;
    max-width: none;
  }
  .print-off {
    display: none !important;
  }
  .tb-page,
  .tb-block {
    break-inside: auto;
  }
  .tb-q,
  .tb-example,
  .tb-formula,
  .tb-def,
  .tb-pitfall,
  .tb-fig {
    break-inside: avoid;
  }
  .tb-page-head,
  .tb-section > h2,
  .tb-test-head,
  .tb-block > h3 {
    break-after: avoid;
  }
  body.textbook-page .grammar-handout-footer {
    break-before: avoid;
    page-break-before: avoid;
    margin-top: 4mm !important;
  }
  .tb-section {
    break-before: page;
  }
  .tb-section.tb-section--first {
    break-before: auto;
  }
  .tb-cover h1 {
    color: #ecfdf5 !important;
  }
  body.show-answers .tb-answer {
    display: block;
    border: 1px solid #86efac;
  }
  .tb-lecture-flow > .tb-fig {
    float: right;
    width: 42%;
    max-width: 72mm;
    margin: 0 0 4mm 5mm;
  }
  .tb-fig img {
    max-height: 55mm;
    width: auto;
    max-width: 100%;
    margin: 0 auto;
  }
}