:root {
  color-scheme: light;
  --g-bg: #f7f4ef;
  --g-surface: #fffdf8;
  --g-surface-2: #f1ebe2;
  --g-text: #1c1914;
  --g-muted: #6b645a;
  --g-border: #e4ddd2;
  --g-accent: #9a3412;
  --g-accent-2: #7c2d12;
  --g-soft: #f3e7dc;
  --g-ink: #292524;
  --g-radius: 14px;
}

[data-theme="dark"] {
  color-scheme: dark;
  --g-bg: #12100e;
  --g-surface: #1c1916;
  --g-surface-2: #26211c;
  --g-text: #f5f0e8;
  --g-muted: #a8a29a;
  --g-border: #3f3a34;
  --g-accent: #fdba74;
  --g-accent-2: #fed7aa;
  --g-soft: #2a2118;
  --g-ink: #faf7f2;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background:
    radial-gradient(circle at top left, color-mix(in srgb, var(--g-soft) 70%, transparent), transparent 40%),
    var(--g-bg);
  color: var(--g-text);
  font-family: "Source Serif 4", "Noto Serif", Georgia, serif;
}
button, input {
  font-family: "IBM Plex Sans", "Noto Sans", system-ui, sans-serif;
}
button, a { -webkit-tap-highlight-color: transparent; }
[hidden] { display: none !important; }

.grammar-shell { min-height: 100vh; }
.grammar-toolbar {
  position: sticky;
  top: 0;
  z-index: 50;
  border-bottom: 1px solid color-mix(in srgb, var(--g-border) 80%, transparent);
  background: color-mix(in srgb, var(--g-surface) 92%, transparent);
  backdrop-filter: blur(16px);
}
.grammar-toolbar__inner {
  min-height: 54px;
  max-width: 920px;
  margin: auto;
  padding: 8px 20px;
  display: flex;
  align-items: center;
  gap: 10px;
}
.grammar-back, .grammar-theme,
.grammar-present-controls button {
  width: 36px;
  height: 36px;
  border: 1px solid var(--g-border);
  border-radius: 10px;
  display: inline-grid;
  place-items: center;
  color: var(--g-text);
  background: var(--g-surface);
  text-decoration: none;
  cursor: pointer;
}
.grammar-segment, .grammar-layers {
  display: flex;
  gap: 3px;
  padding: 3px;
  border-radius: 11px;
  background: var(--g-surface-2);
}
.grammar-segment button, .grammar-layers button {
  border: 0;
  border-radius: 8px;
  padding: 6px 11px;
  color: var(--g-muted);
  background: transparent;
  cursor: pointer;
}
.grammar-segment button.is-active,
.grammar-layers button.is-active {
  color: var(--g-accent-2);
  background: var(--g-surface);
}
.grammar-toolbar__divider {
  height: 24px;
  width: 1px;
  background: var(--g-border);
}
.grammar-present-controls { display: none; gap: 6px; }
.grammar-toolbar__actions { margin-left: auto; display: flex; gap: 8px; align-items: center; }
.grammar-quiz {
  padding: 7px 14px 10px;
  border-radius: 8px;
  color: #fff;
  background: #c2410c;
  box-shadow: 0 3px 0 #9a3412;
  font-weight: 700;
  text-transform: uppercase;
  text-decoration: none;
  font-size: 12px;
}
.grammar-quiz:active { transform: translateY(2px); box-shadow: 0 1px 0 #9a3412; }

/* ── Library (compact TOC) ── */
.grammar-library {
  max-width: 760px;
  margin: auto;
  padding: 48px 20px 72px;
}
.grammar-library__hero { margin-bottom: 28px; }
.grammar-kicker {
  margin: 0 0 8px;
  color: var(--g-accent);
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: .14em;
  text-transform: uppercase;
}
.grammar-library h1 {
  margin: 0;
  font-size: clamp(32px, 6vw, 48px);
  line-height: 1.08;
  letter-spacing: -.03em;
}
.grammar-library__hero > p:not(.grammar-kicker) {
  margin: 10px 0 0;
  color: var(--g-muted);
  font-size: 16px;
  line-height: 1.55;
  max-width: 36em;
}
.grammar-search { margin-top: 22px; }
.grammar-search input {
  width: 100%;
  height: 46px;
  padding: 0 16px;
  border: 1px solid var(--g-border);
  border-radius: 12px;
  outline: none;
  color: var(--g-text);
  background: var(--g-surface);
}
.grammar-search input:focus {
  border-color: var(--g-accent);
  box-shadow: 0 0 0 3px var(--g-soft);
}
.grammar-filters {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 14px;
}
.grammar-filters button {
  border: 1px solid var(--g-border);
  border-radius: 999px;
  padding: 5px 11px;
  color: var(--g-muted);
  background: transparent;
  cursor: pointer;
  font-size: 13px;
}
.grammar-filters button.is-active {
  border-color: var(--g-accent);
  color: var(--g-accent-2);
  background: var(--g-soft);
}

.grammar-grid {
  display: flex;
  flex-direction: column;
  border-top: 1px solid var(--g-border);
}
.grammar-row {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 16px;
  align-items: baseline;
  padding: 14px 4px;
  border-bottom: 1px solid var(--g-border);
  color: inherit;
  text-decoration: none;
  transition: background .15s ease;
}
.grammar-row:hover { background: color-mix(in srgb, var(--g-soft) 55%, transparent); }
.grammar-row__title {
  display: block;
  font-size: 18px;
  font-weight: 600;
  line-height: 1.35;
  letter-spacing: -.01em;
}
.grammar-row__subtitle {
  display: block;
  margin-top: 3px;
  color: var(--g-muted);
  font-size: 14px;
  line-height: 1.4;
}
.grammar-row__side {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  justify-content: flex-end;
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-size: 11px;
}
.grammar-row__tag,
.grammar-row__level,
.grammar-row__quiz {
  padding: 3px 8px;
  border-radius: 999px;
  color: var(--g-muted);
  background: var(--g-surface-2);
  white-space: nowrap;
}
.grammar-row__quiz {
  color: #9a3412;
  background: #ffedd5;
  font-weight: 700;
}
.grammar-loading { color: var(--g-muted); padding: 28px 0; }

/* ── Detail / document reading ── */
.grammar-detail {
  max-width: 720px;
  margin: auto;
  padding: 0 20px 72px;
}
.grammar-hero {
  padding: 48px 0 28px;
  border-bottom: 1px solid var(--g-border);
}
.grammar-hero__back {
  display: inline-block;
  margin-bottom: 24px;
  color: var(--g-muted);
  text-decoration: none;
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-size: 14px;
}
.grammar-hero h1 {
  margin: 0;
  font-size: clamp(30px, 5vw, 46px);
  line-height: 1.15;
  letter-spacing: -.03em;
}
.grammar-title-vi {
  margin: 10px 0 0;
  color: var(--g-accent-2);
  font-size: 18px;
  line-height: 1.4;
}
.grammar-description { display: none; }
.grammar-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 18px;
  font-family: "IBM Plex Sans", system-ui, sans-serif;
}
.grammar-meta span {
  padding: 4px 9px;
  border-radius: 999px;
  color: var(--g-muted);
  background: var(--g-surface-2);
  font-size: 12px;
}

.grammar-reading {
  padding-top: 28px;
}
.grammar-overview,
.grammar-patterns,
.grammar-tips,
.grammar-sources {
  margin: 0;
  padding: 0;
  border: 0;
  background: transparent;
  box-shadow: none;
}

.grammar-doc__heading {
  margin: 0 0 12px;
  font-size: 22px;
  line-height: 1.3;
  letter-spacing: -.02em;
}
.grammar-doc__eyebrow {
  margin: 0 0 6px;
  color: var(--g-accent);
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: .06em;
  text-transform: uppercase;
}
.grammar-doc__lead {
  margin: 0 0 14px;
  color: var(--g-muted);
  font-size: 17px;
  line-height: 1.55;
}
.grammar-doc__prose,
.grammar-doc__prose-block {
  margin: 0 0 14px;
  white-space: pre-line;
  line-height: 1.75;
  font-size: 17px;
}
.grammar-doc__prose p { margin: 0 0 10px; line-height: 1.75; }
.grammar-doc__note {
  margin: 0 0 16px;
  padding-left: 14px;
  border-left: 2px solid var(--g-accent);
  color: var(--g-muted);
  line-height: 1.65;
}
.grammar-doc__section {
  padding: 28px 0;
  border-top: 1px solid var(--g-border);
}
.grammar-doc__section:first-child { border-top: 0; padding-top: 8px; }
.grammar-doc__examples { margin-top: 16px; display: grid; gap: 12px; }
.grammar-doc__example { padding: 0; }
.grammar-doc__hanzi {
  margin: 0;
  font-family: "Noto Sans SC", "Microsoft YaHei", sans-serif;
  font-size: 20px;
  line-height: 1.55;
}
.grammar-doc__pinyin {
  margin: 2px 0 0;
  color: var(--g-accent);
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-size: 14px;
}
.grammar-doc__meaning {
  margin: 2px 0 0;
  color: var(--g-muted);
  font-size: 15px;
  line-height: 1.5;
}

.grammar-shell[data-show-chinese="false"] .grammar-doc__hanzi,
.grammar-shell[data-show-chinese="false"] .grammar-slide__example strong,
.grammar-shell[data-show-pinyin="false"] .grammar-doc__pinyin,
.grammar-shell[data-show-pinyin="false"] .grammar-slide__example small,
.grammar-shell[data-show-meaning="false"] .grammar-doc__meaning,
.grammar-shell[data-show-meaning="false"] .grammar-doc__lead,
.grammar-shell[data-show-meaning="false"] .grammar-slide__meaning,
.grammar-shell[data-show-meaning="false"] .grammar-slide__example span {
  display: none;
}

.grammar-doc__details {
  margin: 18px 0;
  border-top: 1px solid var(--g-border);
  padding-top: 14px;
}
.grammar-doc__details--inline {
  margin: 12px 0 0;
  border-top: 0;
  padding-top: 0;
}
.grammar-doc__details summary {
  cursor: pointer;
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-weight: 600;
  color: var(--g-ink);
}
.grammar-doc__details-body { margin-top: 14px; }
.grammar-doc__tip + .grammar-doc__tip {
  margin-top: 18px;
  padding-top: 16px;
  border-top: 1px dashed var(--g-border);
}
.grammar-doc__tip h3 { margin: 0 0 6px; font-size: 18px; }
.grammar-doc__mini-label {
  margin: 12px 0 4px;
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-size: 12px;
  font-weight: 700;
  color: var(--g-accent);
  text-transform: uppercase;
  letter-spacing: .04em;
}
.grammar-doc__tip ul {
  margin: 0;
  padding-left: 18px;
}
.grammar-doc__tip li { margin: 4px 0; line-height: 1.55; }
.grammar-doc__source-title { margin: 0 0 4px; font-weight: 600; }
.grammar-source-gallery {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 8px 0 16px;
  font-family: "IBM Plex Sans", system-ui, sans-serif;
}
.grammar-source-gallery a { color: var(--g-accent-2); }

.grammar-complete {
  margin-top: 28px;
  padding: 18px 0 0;
  border-top: 1px solid var(--g-border);
  display: flex;
  align-items: center;
  gap: 14px;
}
.grammar-complete > span { display: none; }
.grammar-complete h2 {
  margin: 0;
  font-size: 18px;
}
.grammar-complete p {
  margin: 4px 0 0;
  color: var(--g-muted);
  font-size: 14px;
}
.grammar-complete a {
  margin-left: auto;
  color: var(--g-accent-2);
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-weight: 700;
  text-decoration: none;
}

/* ── Presentation slides ── */
.grammar-shell[data-mode="presentation"] .grammar-site-header,
body[data-grammar-mode="presentation"] .grammar-site-header,
.grammar-shell[data-mode="presentation"] .grammar-hero { display: none; }
.grammar-shell[data-mode="presentation"] [data-reading-only] { display: none; }
.grammar-shell[data-mode="presentation"] .grammar-present-controls { display: flex; }
.grammar-shell[data-mode="presentation"] .grammar-reading { display: none !important; }
body[data-grammar-mode="presentation"] { overflow: hidden; }
.grammar-shell[data-mode="presentation"] .grammar-detail {
  max-width: none;
  padding: 0;
}
.grammar-presentation {
  height: calc(100vh - 54px);
  padding: 18px;
  display: flex;
}
.grammar-slide {
  width: min(920px, 100%);
  height: 100%;
  margin: auto;
  padding: clamp(28px, 5vw, 56px);
  border: 1px solid var(--g-border);
  border-radius: 22px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  background: var(--g-surface);
  overflow: hidden;
  position: relative;
}
.grammar-slide__count {
  position: absolute;
  top: clamp(16px, 3vw, 28px);
  right: clamp(16px, 3vw, 28px);
  color: var(--g-muted);
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-size: 13px;
}
.grammar-slide__type {
  margin: 0 0 10px;
  color: var(--g-accent);
  font-family: "IBM Plex Sans", system-ui, sans-serif;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .05em;
  font-size: 12px;
}
.grammar-slide__pattern {
  margin: 0;
  max-width: 860px;
  font-family: "Noto Sans SC", "Microsoft YaHei", "Source Serif 4", serif;
  font-size: clamp(26px, 4.8vw, 48px);
  line-height: 1.25;
  letter-spacing: -.02em;
}
.grammar-slide[data-kind="title"] .grammar-slide__pattern {
  font-size: clamp(34px, 6vw, 58px);
}
.grammar-slide[data-kind="example"] .grammar-slide__pattern {
  font-family: "Noto Sans SC", "Microsoft YaHei", sans-serif;
  font-size: clamp(28px, 5vw, 52px);
}
.grammar-slide__meaning {
  margin: 14px 0 0;
  color: var(--g-accent-2);
  font-size: clamp(16px, 2.2vw, 22px);
  line-height: 1.45;
  max-width: 42em;
}
.grammar-slide__usage {
  max-width: 720px;
  margin: 20px 0 0;
  color: var(--g-ink);
  font-size: clamp(15px, 1.7vw, 18px);
  line-height: 1.65;
  overflow: hidden;
}
.grammar-slide__usage p {
  margin: 0 0 10px;
}
.grammar-slide__usage p:last-child { margin-bottom: 0; }
.grammar-slide__list {
  margin: 0;
  padding-left: 1.15em;
}
.grammar-slide__list li {
  margin: 0 0 8px;
}
.grammar-slide__list li:last-child { margin-bottom: 0; }
.grammar-slide__paras p { margin: 0 0 10px; }
.grammar-slide__example { display: none; }
.grammar-slide__dots {
  display: flex;
  gap: 3px;
  margin-top: auto;
  padding-top: 28px;
  max-width: 100%;
  overflow: hidden;
}
.grammar-slide__dots i {
  height: 3px;
  flex: 1;
  min-width: 4px;
  max-width: 48px;
  border-radius: 4px;
  background: var(--g-border);
}
.grammar-slide__dots i.is-active { background: var(--g-accent); }
.grammar-error {
  max-width: 720px;
  margin: 48px auto;
  padding: 20px;
  color: #991b1b;
  background: #fee2e2;
  border-radius: 12px;
}

@media (max-width: 700px) {
  .grammar-row {
    grid-template-columns: 1fr;
    gap: 8px;
  }
  .grammar-row__side { justify-content: flex-start; }
  .grammar-toolbar__inner { padding-inline: 12px; gap: 6px; }
  .grammar-toolbar__divider { display: none; }
  .grammar-complete { flex-wrap: wrap; }
  .grammar-complete a { margin-left: 0; }
}
@media (max-width: 560px) {
  .grammar-library { padding: 32px 16px 56px; }
  .grammar-detail { padding-inline: 16px; }
  .grammar-hero { padding-top: 32px; }
  .grammar-segment button { padding-inline: 8px; font-size: 12px; }
  .grammar-layers button { padding: 6px 7px; font-size: 12px; }
  .grammar-presentation { padding: 8px; }
  .grammar-slide { border-radius: 16px; padding: 20px; }
  .grammar-theme { display: none; }
}