:root {
  --bg: #f5f0e7;
  --paper: #fffaf2;
  --paper-strong: #fffdf8;
  --ink: #16120d;
  --muted: #5a4f45;
  --line: rgba(22, 18, 13, 0.14);
  --accent: #782f1d;
  --accent-soft: rgba(120, 47, 29, 0.12);
  --olive: #646f43;
  --olive-soft: rgba(100, 111, 67, 0.15);
  --navy: #283c52;
  --navy-soft: rgba(40, 60, 82, 0.15);
  --gold: #c49a3f;
  --shadow: 0 20px 60px rgba(35, 25, 17, 0.08);
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 32px;
  --space-7: 48px;
  --space-8: 64px;
  --max-text: 72ch;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(circle at top left, rgba(196, 154, 63, 0.18), transparent 26%),
    radial-gradient(circle at bottom right, rgba(100, 111, 67, 0.16), transparent 22%),
    var(--bg);
  font-family: "Gelasio", "Palatino Linotype", Georgia, serif;
  line-height: 1.6;
}

button,
input,
summary {
  font: inherit;
}

.page-shell {
  display: grid;
  grid-template-columns: minmax(260px, 320px) 1fr;
  min-height: 100vh;
}

.sidebar {
  border-right: 1px solid var(--line);
  background: rgba(255, 250, 242, 0.8);
  backdrop-filter: blur(8px);
}

.sidebar__inner {
  position: sticky;
  top: 0;
  display: grid;
  gap: var(--space-5);
  padding: var(--space-6) var(--space-5) var(--space-6);
  min-height: 100vh;
}

.eyebrow {
  margin: 0;
  text-transform: uppercase;
  letter-spacing: 0.18em;
  font-size: 0.78rem;
  color: var(--muted);
}

.sidebar__title,
.hero__title {
  margin: 0;
  line-height: 0.95;
  font-weight: 700;
}

.sidebar__title {
  font-size: clamp(2.6rem, 3vw, 4.2rem);
}

.sidebar__copy,
.hero__lead,
.notice__body {
  margin: 0;
  max-width: var(--max-text);
  color: var(--muted);
}

.search {
  display: grid;
  gap: var(--space-2);
}

.search__label {
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--muted);
}

.search input {
  width: 100%;
  border: 1px solid var(--line);
  background: var(--paper-strong);
  padding: 14px 16px;
  border-radius: 14px;
  color: var(--ink);
}

.toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
}

.toolbar__button {
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper-strong);
  padding: 10px 14px;
  border-radius: 999px;
  cursor: pointer;
  transition: transform 160ms ease, background 160ms ease;
}

.toolbar__button:hover,
.toolbar__button:focus-visible {
  transform: translateY(-1px);
}

.toolbar__button--ghost {
  background: transparent;
  color: var(--ink);
}

.unit-nav {
  display: grid;
  gap: var(--space-2);
  align-content: start;
}

.unit-nav a {
  display: block;
  padding: 10px 12px;
  border-radius: 12px;
  color: var(--ink);
  text-decoration: none;
  border: 1px solid transparent;
  transition: background 160ms ease, border-color 160ms ease;
}

.unit-nav a:hover,
.unit-nav a:focus-visible,
.unit-nav a.is-active {
  background: var(--paper);
  border-color: var(--line);
}

.unit-nav__meta {
  display: block;
  margin-top: 2px;
  color: var(--muted);
  font-size: 0.9rem;
}

.content {
  padding: var(--space-7) clamp(20px, 4vw, 56px) var(--space-8);
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.8fr) minmax(260px, 1fr);
  gap: var(--space-6);
  align-items: start;
  margin-bottom: var(--space-6);
}

.hero__title {
  font-size: clamp(2.7rem, 6vw, 5.4rem);
  margin-bottom: var(--space-4);
  max-width: 12ch;
}

.hero__meta {
  display: grid;
  gap: var(--space-4);
}

.hero-card {
  border: 1px solid var(--line);
  border-radius: 20px;
  background: var(--paper);
  padding: var(--space-5);
  box-shadow: var(--shadow);
}

.hero-card__label,
.hero-card__note,
.notice__title {
  margin: 0;
}

.hero-card__label {
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.12em;
  font-size: 0.76rem;
}

.hero-card__value {
  margin: var(--space-2) 0;
  font-size: 1.7rem;
  font-weight: 700;
}

.hero-card__note {
  color: var(--muted);
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-bottom: var(--space-5);
}

.legend-chip {
  border-radius: 999px;
  padding: 9px 14px;
  font-size: 0.92rem;
  border: 1px solid var(--line);
  background: var(--paper);
}

.legend-chip--explain { background: rgba(120, 47, 29, 0.08); }
.legend-chip--example { background: rgba(100, 111, 67, 0.1); }
.legend-chip--summary { background: rgba(40, 60, 82, 0.1); color: var(--navy); }
.legend-chip--exam { background: rgba(196, 154, 63, 0.16); }

.notice {
  padding: var(--space-5);
  border: 1px solid var(--line);
  border-radius: 24px;
  background: linear-gradient(135deg, rgba(255, 253, 248, 0.95), rgba(246, 237, 222, 0.9));
  margin-bottom: var(--space-6);
}

.notice__title {
  margin-bottom: var(--space-2);
  font-size: 1.2rem;
}

.units {
  display: grid;
  gap: var(--space-5);
}

.unit {
  border: 1px solid var(--line);
  border-radius: 30px;
  background: var(--paper);
  box-shadow: var(--shadow);
  overflow: hidden;
  opacity: 0;
  transform: translateY(18px);
  animation: unit-in 480ms cubic-bezier(.2,.7,.2,1) forwards;
}

.unit:nth-child(2) { animation-delay: 40ms; }
.unit:nth-child(3) { animation-delay: 80ms; }
.unit:nth-child(4) { animation-delay: 120ms; }

@keyframes unit-in {
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.unit > summary {
  list-style: none;
  cursor: pointer;
  padding: var(--space-6);
  display: grid;
  gap: var(--space-4);
  background:
    linear-gradient(135deg, rgba(255, 255, 255, 0.42), transparent 40%),
    linear-gradient(180deg, rgba(120, 47, 29, 0.03), transparent);
}

.unit > summary::-webkit-details-marker {
  display: none;
}

.unit__header {
  display: flex;
  justify-content: space-between;
  align-items: start;
  gap: var(--space-4);
}

.unit__badge {
  display: inline-flex;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 8px 12px;
  font-size: 0.84rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
}

.unit__title {
  margin: 0 0 var(--space-2);
  font-size: clamp(1.6rem, 3vw, 2.3rem);
}

.unit__subtitle,
.unit__pages {
  margin: 0;
  color: var(--muted);
}

.unit__body {
  padding: 0 var(--space-6) var(--space-6);
  display: grid;
  gap: var(--space-5);
}

.section-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: var(--space-4);
}

.study-card {
  border: 1px solid var(--line);
  border-radius: 22px;
  padding: var(--space-5);
  background: var(--paper-strong);
}

.study-card--explain { box-shadow: inset 0 0 0 1px rgba(120, 47, 29, 0.04); }
.study-card--example { box-shadow: inset 0 0 0 1px rgba(100, 111, 67, 0.05); }
.study-card--summary { box-shadow: inset 0 0 0 1px rgba(40, 60, 82, 0.06); }
.study-card--exam { box-shadow: inset 0 0 0 1px rgba(196, 154, 63, 0.08); }

.study-card__kicker {
  margin: 0 0 var(--space-3);
  text-transform: uppercase;
  letter-spacing: 0.12em;
  font-size: 0.76rem;
  color: var(--muted);
}

.study-card__title {
  margin: 0 0 var(--space-3);
  font-size: 1.22rem;
}

.bilingual-block {
  display: grid;
  gap: var(--space-3);
}

.bilingual-line {
  padding-top: var(--space-3);
  border-top: 1px solid rgba(22, 18, 13, 0.08);
}

.bilingual-line:first-child {
  padding-top: 0;
  border-top: 0;
}

.lang-label {
  display: inline-block;
  margin-bottom: var(--space-1);
  font-size: 0.74rem;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--muted);
}

.bilingual-line p {
  margin: 0;
}

.summary-list,
.focus-list,
.quiz-list {
  margin: 0;
  padding-left: 1.1rem;
}

.summary-columns {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: var(--space-4);
}

.memory-tip {
  border-top: 1px dashed var(--line);
  margin-top: var(--space-4);
  padding-top: var(--space-4);
  color: var(--muted);
}

.comparison-wrap {
  overflow-x: auto;
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  min-width: 720px;
}

.comparison-table th,
.comparison-table td {
  padding: 14px 16px;
  vertical-align: top;
  border-bottom: 1px solid var(--line);
  text-align: left;
}

.comparison-table th {
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--muted);
}

.quiz-item + .quiz-item,
.focus-item + .focus-item {
  margin-top: var(--space-3);
}

.source {
  border: 1px solid var(--line);
  border-radius: 22px;
  background: #f7f1e8;
  padding: var(--space-4);
}

.source > summary {
  cursor: pointer;
  font-weight: 700;
}

.source__grid {
  display: grid;
  gap: var(--space-4);
  margin-top: var(--space-4);
}

.source-page {
  border: 1px solid rgba(22, 18, 13, 0.1);
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.6);
  padding: var(--space-4);
}

.source-page__title {
  margin: 0 0 var(--space-2);
  font-size: 0.95rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
}

.source-page pre {
  margin: 0;
  white-space: pre-wrap;
  word-break: break-word;
  font-family: "Ubuntu Mono", Consolas, monospace;
  font-size: 0.92rem;
  line-height: 1.55;
}

.footer-note {
  color: var(--muted);
  font-size: 0.94rem;
}

body.summary-mode .section-grid:not(.section-grid--summary),
body.summary-mode .comparison-wrap,
body.summary-mode .source,
body.summary-mode .study-card--exam:not(.study-card--summary) {
  display: none;
}

@media (max-width: 1040px) {
  .page-shell {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .sidebar__inner {
    position: static;
    min-height: auto;
  }

  .hero {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 720px) {
  .content {
    padding: var(--space-5) 16px var(--space-7);
  }

  .sidebar__inner {
    padding: var(--space-5) 16px;
  }

  .unit > summary,
  .unit__body {
    padding-left: var(--space-4);
    padding-right: var(--space-4);
  }

  .hero__title {
    max-width: 100%;
  }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .unit,
  .toolbar__button {
    animation: none;
    transition: none;
    transform: none;
  }
}