:root {
  color-scheme: light;
  --ink: #202124;
  --muted: #667085;
  --line: #d7dde6;
  --soft-line: #e8edf3;
  --panel: #ffffff;
  --panel-soft: #f6f8fb;
  --wash: #eef3f8;
  --accent: #1f7a6d;
  --accent-strong: #0f5f54;
  --gold: #a36b00;
  --rose: #b34c62;
  --shadow: 0 16px 42px rgba(32, 33, 36, 0.1);
  font-family:
    "Inter", "Segoe UI", "Noto Sans SC", "Noto Sans JP", system-ui, sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-width: 320px;
  background: var(--wash);
  color: var(--ink);
}

button,
input {
  font: inherit;
}

.app-shell {
  display: grid;
  grid-template-columns: 320px minmax(0, 1fr);
  min-height: 100vh;
}

.sidebar {
  position: sticky;
  top: 0;
  height: 100vh;
  overflow: auto;
  padding: 22px 18px;
  background: #fbfcfe;
  border-right: 1px solid var(--line);
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 22px;
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 42px;
  height: 42px;
  border-radius: 8px;
  background: var(--accent);
  color: #fff;
  font-weight: 800;
}

.brand h1 {
  margin: 0;
  font-size: 18px;
}

.brand p,
.status-line,
.meta-row,
.source-link,
.empty-note {
  margin: 0;
  color: var(--muted);
  font-size: 13px;
}

.search-box {
  display: grid;
  gap: 7px;
  margin-bottom: 16px;
  color: var(--muted);
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
}

.search-box input {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  background: #fff;
  color: var(--ink);
}

.lesson-nav,
.search-results {
  display: grid;
  gap: 8px;
}

.lesson-group {
  margin-top: 16px;
}

.lesson-group h2 {
  margin: 0 0 8px;
  color: var(--muted);
  font-size: 12px;
}

.lesson-link,
.search-result {
  width: 100%;
  border: 1px solid transparent;
  border-radius: 8px;
  padding: 10px 11px;
  background: transparent;
  color: var(--ink);
  text-align: left;
  cursor: pointer;
}

.lesson-link:hover,
.search-result:hover,
.lesson-link.active {
  border-color: var(--line);
  background: #fff;
}

.lesson-link strong,
.search-result strong {
  display: block;
  margin-bottom: 4px;
  font-size: 14px;
}

.lesson-link span,
.search-result span {
  color: var(--muted);
  font-size: 12px;
}

.reader {
  min-width: 0;
}

.reader-topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  gap: 12px;
  min-height: 58px;
  padding: 12px 28px;
  border-bottom: 1px solid var(--line);
  background: rgba(238, 243, 248, 0.92);
  backdrop-filter: blur(12px);
}

.icon-button {
  display: none;
  width: 38px;
  height: 38px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  cursor: pointer;
}

.lesson-view {
  max-width: 1120px;
  margin: 0 auto;
  padding: 28px;
}

.lesson-hero {
  padding-bottom: 22px;
  border-bottom: 1px solid var(--line);
}

.lesson-hero h2 {
  margin: 7px 0 9px;
  font-size: clamp(28px, 4vw, 46px);
  line-height: 1.08;
}

.meta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.meta-row span {
  min-width: 0;
  overflow-wrap: anywhere;
}

.metric-row {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 10px;
  margin: 18px 0 26px;
}

.metric {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 12px;
  background: var(--panel);
}

.metric b {
  display: block;
  font-size: 22px;
}

.metric span {
  color: var(--muted);
  font-size: 12px;
}

.section-title {
  margin: 30px 0 12px;
  font-size: 18px;
}

.review-grid,
.grammar-list,
.practice-list,
.raw-list {
  display: grid;
  gap: 14px;
}

.grammar-card,
.practice-card,
.review-card {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  box-shadow: var(--shadow);
}

.grammar-card {
  overflow: hidden;
}

.grammar-head {
  padding: 16px 18px;
  border-bottom: 1px solid var(--soft-line);
  background: linear-gradient(90deg, #ffffff, #f5fbf9);
}

.grammar-head h3 {
  margin: 0 0 8px;
  font-size: 21px;
}

.meaning-list,
.connection-list,
.usage-list {
  margin: 8px 0 0;
  padding-left: 20px;
}

.grammar-field {
  display: grid;
  gap: 6px;
  margin-top: 10px;
}

.grammar-field ul {
  display: grid;
  gap: 7px;
  margin: 0;
  padding-left: 0;
  list-style: none;
}

.grammar-field li {
  display: grid;
  gap: 3px;
  line-height: 1.55;
}

.field-label {
  color: var(--muted);
  font-size: 12px;
  font-weight: 800;
  text-transform: uppercase;
}

.jp-text {
  color: var(--muted);
  font-size: 13px;
}

.zh-text {
  color: var(--ink);
  font-weight: 650;
}

.examples {
  display: grid;
  gap: 12px;
  padding: 16px;
}

.example-card {
  border: 1px solid var(--soft-line);
  border-radius: 8px;
  background: var(--panel-soft);
  overflow: hidden;
}

.example-main {
  padding: 14px 15px;
}

.sentence {
  margin: 0;
  font-size: 18px;
  line-height: 1.65;
}

.translation {
  display: inline-flex;
  margin-top: 10px;
  padding: 8px 10px;
  border-radius: 8px;
  background: #e8f4f1;
  color: var(--accent-strong);
  font-size: 14px;
  line-height: 1.5;
}

.explanation-toggle {
  width: 100%;
  border: 0;
  border-top: 1px solid var(--soft-line);
  padding: 11px 15px;
  background: #fff;
  color: var(--accent-strong);
  text-align: left;
  cursor: pointer;
  font-weight: 700;
}

.explanation {
  display: none;
  padding: 0 18px 16px;
  background: #fff;
}

.example-card.open .explanation {
  display: block;
}

.explanation ul {
  margin: 12px 0 0;
  padding-left: 21px;
}

.explanation li {
  margin: 9px 0;
  line-height: 1.7;
}

.explanation strong {
  color: var(--accent-strong);
}

.notes {
  margin: 10px 0 0;
  color: var(--rose);
  font-size: 13px;
}

.practice-card {
  padding: 15px;
}

.practice-card h3 {
  margin: 0 0 12px;
}

.question {
  padding: 10px 0;
  border-top: 1px solid var(--soft-line);
}

.question:first-of-type {
  border-top: 0;
}

.choices {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 8px;
}

.choice {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 6px 9px;
  background: #fff;
  font-size: 13px;
  color: var(--ink);
  cursor: pointer;
}

.choice.selected {
  border-color: var(--accent);
}

.question.correct .answer-note {
  color: #177245;
}

.question.incorrect .answer-note {
  color: #b42318;
}

.answer-note {
  margin: 8px 0 0;
  color: var(--muted);
  font-size: 13px;
}

.practice-explanation {
  margin-top: 14px;
  padding: 12px 14px;
  background: #fdfaf5;
  border-radius: 6px;
  border-left: 3px solid var(--accent);
  font-size: 14px;
  line-height: 1.75;
}

.practice-explanation p {
  margin: 0.4em 0;
}

.practice-explanation ul {
  margin: 0.3em 0;
  padding-left: 1.3em;
}

.practice-explanation li {
  margin-bottom: 0.15em;
}

.practice-explanation strong {
  color: #5c3d1a;
}

.practice-explanation hr {
  border: none;
  border-top: 1px dashed #d9d0bd;
  margin: 0.6em 0;
}

.source-link {
  display: inline-flex;
  align-items: center;
  min-height: 32px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 5px 10px;
  background: #fff;
  cursor: pointer;
}

.raw-panel {
  margin-top: 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  background: #111827;
  color: #f9fafb;
  white-space: pre-wrap;
  overflow: auto;
  line-height: 1.55;
}

.hidden {
  display: none;
}

@media (max-width: 860px) {
  .app-shell {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: fixed;
    z-index: 20;
    inset: 0 auto 0 0;
    width: min(86vw, 340px);
    transform: translateX(-100%);
    transition: transform 160ms ease;
    box-shadow: var(--shadow);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .icon-button {
    display: grid;
    place-items: center;
  }

  .reader-topbar {
    padding: 10px 16px;
  }

  .lesson-view {
    padding: 20px 14px 32px;
  }

  .lesson-hero .meta-row {
    display: grid;
    gap: 6px;
  }

  .metric-row {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

/* EPUB download buttons */
.epub-links { margin-top: 0.6em; }
.epub-download, .epub-all-link a {
  display: inline-block;
  padding: 0.35em 0.9em;
  border: 1px solid var(--line);
  border-radius: 6px;
  text-decoration: none;
  font-size: 0.85em;
  color: var(--ink);
}
.epub-download:hover, .epub-all-link a:hover {
  background: var(--panel-soft);
  border-color: var(--accent);
}
.epub-all-link {
  padding: 0.8em;
  border-top: 1px solid var(--line);
}

@media (max-width: 520px) {
  .metric-row {
    grid-template-columns: 1fr;
  }

  .lesson-hero h2 {
    font-size: 30px;
  }

  .sentence {
    font-size: 16px;
  }
}