/* ==========================================================================
   Modular App — single stylesheet, mobile-first
   ========================================================================== */

/* --- Custom properties --- */
:root,
[data-theme="light"] {
  --bg: #f4f6f9;
  --bg-elevated: #ffffff;
  --bg-muted: #e8ecf1;
  --text: #1a1d23;
  --text-muted: #5c6570;
  --border: #d0d7e0;
  --primary: #3b6ef5;
  --primary-hover: #2d5ad4;
  --primary-soft: rgba(59, 110, 245, 0.12);
  --accent: #0d9488;
  --danger: #dc2626;
  --danger-hover: #b91c1c;
  --danger-soft: rgba(220, 38, 38, 0.1);
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.08), 0 4px 12px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.1);
  --radius: 12px;
  --radius-sm: 8px;
  --nav-height: 56px;
  --font: system-ui, -apple-system, "Segoe UI", Roboto, Ubuntu, sans-serif;
  --serif: Georgia, "Iowan Old Style", Palatino, "Palatino Linotype", serif;
  --study: #9a3412;
  --study-soft: rgba(154, 52, 18, 0.12);
  --transition: 180ms ease;
  color-scheme: light;
}

[data-theme="dark"] {
  --bg: #0f1117;
  --bg-elevated: #1a1d27;
  --bg-muted: #252836;
  --text: #e8eaef;
  --text-muted: #9aa3b2;
  --border: #2e3340;
  --primary: #6b8cff;
  --primary-hover: #8aa4ff;
  --primary-soft: rgba(107, 140, 255, 0.18);
  --accent: #2dd4bf;
  --danger: #f87171;
  --danger-hover: #fca5a5;
  --danger-soft: rgba(248, 113, 113, 0.15);
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.3), 0 4px 12px rgba(0, 0, 0, 0.2);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.4);
  --study: #fdba74;
  --study-soft: rgba(253, 186, 116, 0.16);
  color-scheme: dark;
}

/* --- Reset --- */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.55;
  min-height: 100dvh;
  transition: background var(--transition), color var(--transition);
}

img {
  max-width: 100%;
  display: block;
}

button,
input,
select {
  font: inherit;
  color: inherit;
}

a {
  color: var(--primary);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

ul {
  list-style: none;
}

/* --- App shell --- */
#app {
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
}

.module-root {
  flex: 1;
  width: 100%;
  max-width: 1100px;
  margin: 0 auto;
  padding: calc(var(--nav-height) + 1rem) 1rem 2rem;
}

.module {
  display: none;
  animation: fadeIn 220ms ease;
}

.module.is-active {
  display: block;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(6px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* --- Navbar --- */
.navbar-root {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: var(--nav-height);
  background: var(--bg-elevated);
  border-bottom: 1px solid var(--border);
  box-shadow: var(--shadow);
  transition: background var(--transition), border-color var(--transition);
}

.navbar {
  height: 100%;
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 0.75rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
}

.navbar__brand {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.02em;
  color: var(--text);
  white-space: nowrap;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.35rem 0.4rem;
  border-radius: var(--radius-sm);
}

.navbar__brand:hover,
.navbar__brand:focus-visible {
  color: var(--primary);
  outline: none;
}

.navbar__brand:focus-visible {
  box-shadow: 0 0 0 2px var(--primary-soft);
}

.navbar__toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 42px;
  height: 42px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-muted);
  cursor: pointer;
  transition: background var(--transition), border-color var(--transition);
}

.navbar__toggle:hover {
  background: var(--primary-soft);
  border-color: var(--primary);
}

.navbar__toggle:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
}

.navbar__toggle-icon {
  display: flex;
  flex-direction: column;
  gap: 5px;
  width: 18px;
}

.navbar__toggle-icon span {
  display: block;
  height: 2px;
  background: var(--text);
  border-radius: 1px;
  transition: transform var(--transition), opacity var(--transition);
}

.navbar.is-open .navbar__toggle-icon span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.navbar.is-open .navbar__toggle-icon span:nth-child(2) {
  opacity: 0;
}

.navbar.is-open .navbar__toggle-icon span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

.navbar__menu {
  display: none;
  position: absolute;
  top: var(--nav-height);
  left: 0;
  right: 0;
  background: var(--bg-elevated);
  border-bottom: 1px solid var(--border);
  padding: 0.5rem;
  flex-direction: column;
  gap: 0.25rem;
  box-shadow: var(--shadow-lg);
}

.navbar.is-open .navbar__menu {
  display: flex;
}

.navbar__link {
  display: block;
  width: 100%;
  text-align: left;
  padding: 0.75rem 1rem;
  border: none;
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--text-muted);
  font-weight: 500;
  cursor: pointer;
  transition: background var(--transition), color var(--transition);
}

.navbar__link:hover,
.navbar__link:focus-visible {
  background: var(--primary-soft);
  color: var(--primary);
  outline: none;
}

.navbar__link.is-active {
  background: var(--primary-soft);
  color: var(--primary);
  font-weight: 600;
}

/* Desktop navbar */
@media (min-width: 768px) {
  .navbar {
    padding: 0 1.25rem;
  }

  .navbar__toggle {
    display: none;
  }

  .navbar__menu {
    display: flex;
    position: static;
    flex-direction: row;
    align-items: center;
    gap: 0.25rem;
    background: transparent;
    border: none;
    box-shadow: none;
    padding: 0;
  }

  .navbar__link {
    width: auto;
    padding: 0.45rem 0.85rem;
    font-size: 0.925rem;
  }
}

/* --- Typography & layout helpers --- */
.page-header {
  margin-bottom: 1.5rem;
}

.page-header h1 {
  font-size: 1.65rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.25;
  margin-bottom: 0.4rem;
}

.page-header p {
  color: var(--text-muted);
  font-size: 0.975rem;
  max-width: 36rem;
}

@media (min-width: 768px) {
  .page-header h1 {
    font-size: 2rem;
  }

  .page-header p {
    font-size: 1.05rem;
  }
}

/* --- Hero / landing --- */
.hero {
  background: linear-gradient(135deg, var(--primary-soft), var(--bg-elevated));
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.75rem 1.25rem;
  margin-bottom: 1.75rem;
  box-shadow: var(--shadow);
}

.hero h1 {
  font-size: 1.75rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  margin-bottom: 0.65rem;
}

.hero p {
  color: var(--text-muted);
  margin-bottom: 1.25rem;
  max-width: 32rem;
}

.hero__actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
}

@media (min-width: 768px) {
  .hero {
    padding: 2.5rem 2rem;
  }

  .hero h1 {
    font-size: 2.35rem;
  }
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  padding: 0.65rem 1.15rem;
  border-radius: var(--radius-sm);
  border: 1px solid transparent;
  font-weight: 600;
  font-size: 0.925rem;
  cursor: pointer;
  transition: background var(--transition), color var(--transition),
    border-color var(--transition), box-shadow var(--transition);
}

.btn:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
}

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

.btn--primary:hover {
  background: var(--primary-hover);
}

.btn--secondary {
  background: var(--bg-elevated);
  color: var(--text);
  border-color: var(--border);
}

.btn--secondary:hover {
  background: var(--bg-muted);
  border-color: var(--primary);
  color: var(--primary);
}

.btn--danger {
  background: var(--danger);
  color: #fff;
}

.btn--danger:hover {
  background: var(--danger-hover);
}

.btn--ghost {
  background: transparent;
  color: var(--text-muted);
  border-color: var(--border);
}

.btn--ghost:hover {
  color: var(--text);
  background: var(--bg-muted);
}

.btn--sm {
  padding: 0.4rem 0.75rem;
  font-size: 0.85rem;
}

.btn:disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

/* --- Cards --- */
.card-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  margin-bottom: 1.75rem;
}

@media (min-width: 540px) {
  .card-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 900px) {
  .card-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

.card {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  box-shadow: var(--shadow);
  transition: border-color var(--transition), box-shadow var(--transition),
    transform var(--transition);
}

.card:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-lg);
  transform: translateY(-2px);
}

.card__icon {
  width: 40px;
  height: 40px;
  border-radius: 10px;
  background: var(--primary-soft);
  color: var(--primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.15rem;
  margin-bottom: 0.85rem;
  font-weight: 700;
}

.card h3 {
  font-size: 1.05rem;
  margin-bottom: 0.4rem;
  letter-spacing: -0.02em;
}

.card p {
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-bottom: 0.85rem;
}

.card__meta {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-weight: 500;
}

/* --- Content blocks --- */
.content-block {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  margin-bottom: 1.25rem;
  box-shadow: var(--shadow);
}

.content-block--spaced {
  margin-top: 1.25rem;
}

.content-block h2 {
  font-size: 1.15rem;
  margin-bottom: 0.65rem;
  letter-spacing: -0.02em;
}

.content-block p {
  color: var(--text-muted);
  font-size: 0.95rem;
  margin-bottom: 0.75rem;
}

.content-block p:last-child {
  margin-bottom: 0;
}

.content-block ul {
  list-style: disc;
  padding-left: 1.25rem;
  color: var(--text-muted);
  font-size: 0.95rem;
}

.content-block li {
  margin-bottom: 0.35rem;
}

.placeholder-bar {
  height: 10px;
  border-radius: 6px;
  background: var(--bg-muted);
  margin-bottom: 0.55rem;
}

.placeholder-bar:last-child {
  margin-bottom: 0;
}

.placeholder-bar--short {
  width: 55%;
}

.placeholder-bar--medium {
  width: 78%;
}

/* --- Section feature list --- */
.feature-list {
  display: grid;
  gap: 0.75rem;
}

.feature-item {
  display: flex;
  gap: 0.85rem;
  align-items: flex-start;
  padding: 1rem;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}

.feature-item__badge {
  flex-shrink: 0;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--primary-soft);
  color: var(--primary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.8rem;
  font-weight: 700;
}

.feature-item h3 {
  font-size: 0.975rem;
  margin-bottom: 0.2rem;
}

.feature-item p {
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* --- Settings --- */
.settings-panel {
  display: grid;
  gap: 1.25rem;
  /*max-width: 520px;*/
  place-items: center;
}

.settings-group {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  box-shadow: var(--shadow);
  width: 100%;
}

.settings-group h2 {
  font-size: 1.05rem;
  margin-bottom: 0.35rem;
}

.settings-group > p {
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-bottom: 1rem;
}

.theme-switch {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.theme-option {
  flex: 1;
  min-width: 120px;
  padding: 0.85rem 1rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg);
  cursor: pointer;
  text-align: center;
  font-weight: 600;
  font-size: 0.9rem;
  transition: border-color var(--transition), background var(--transition),
    color var(--transition);
}

.theme-option:hover {
  border-color: var(--primary);
  color: var(--primary);
}

.theme-option:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
}

.theme-option.is-selected {
  border-color: var(--primary);
  background: var(--primary-soft);
  color: var(--primary);
}

.theme-option span {
  display: block;
  font-size: 1.4rem;
  margin-bottom: 0.35rem;
}

.settings-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  align-items: center;
}

.toast {
  margin-top: 0.85rem;
  padding: 0.65rem 0.85rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  font-weight: 500;
  display: none;
}

.toast.is-visible {
  display: block;
}

.toast--success {
  background: rgba(13, 148, 136, 0.15);
  color: var(--accent);
  border: 1px solid rgba(13, 148, 136, 0.35);
}

.toast--warning {
  background: var(--danger-soft);
  color: var(--danger);
  border: 1px solid rgba(220, 38, 38, 0.3);
}

/* --- Footer note --- */
.module-footer {
  margin-top: 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
  color: var(--text-muted);
  font-size: 0.8rem;
  text-align: center;
}

/* --- Utilities --- */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.text-muted {
  color: var(--text-muted);
}

/* ==========================================================================
   Library & Economics Study Module Styles
   ========================================================================== */

/* --- Reading progress bar --- */
.readbar {
  position: fixed;
  top: var(--nav-height);
  left: 0;
  right: 0;
  height: 3px;
  background: transparent;
  z-index: 99;
}

.readbar [data-readbar-fill] {
  display: block;
  height: 100%;
  width: 0%;
  background: var(--primary);
  transition: width 100ms ease-out;
}

/* --- Library Headers & Mastheads --- */
.lib-mast {
  margin-bottom: 1.5rem;
}

.kicker {
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--primary);
  margin-bottom: 0.25rem;
}

.lib-mast h1 {
  font-size: 1.75rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  margin-bottom: 0.5rem;
}

.lede {
  color: var(--text-muted);
  font-size: 1.05rem;
  line-height: 1.5;
  max-width: 42rem;
}

/* --- Search Form --- */
.lib-search {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1.5rem;
}

.lib-search input[type="search"] {
  flex: 1;
  padding: 0.65rem 1rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  font-size: 0.95rem;
}

.lib-search input[type="search"]:focus {
  outline: 2px solid var(--primary);
  border-color: transparent;
}

/* --- Progress Meter & Course Stats --- */
.course-progress {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  margin-bottom: 1.75rem;
  box-shadow: var(--shadow);
}

.meter {
  height: 8px;
  background: var(--bg-muted);
  border-radius: 4px;
  overflow: hidden;
  margin-bottom: 0.5rem;
}

.meter span {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  transition: width 300ms ease;
}

.meter--lg {
  height: 12px;
  border-radius: 6px;
}

.course-progress p {
  font-size: 0.875rem;
  color: var(--text-muted);
  font-weight: 500;
}

/* --- Unit Cards & Grid --- */
.lib-section-label {
  font-size: 1.2rem;
  font-weight: 700;
  margin-bottom: 1rem;
  letter-spacing: -0.02em;
}

.unit-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  margin-bottom: 2rem;
}

@media (min-width: 640px) {
  .unit-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

.unit-card {
  display: flex;
  gap: 1rem;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  box-shadow: var(--shadow);
  color: inherit;
  transition: border-color var(--transition), transform var(--transition), box-shadow var(--transition);
}

.unit-card:hover {
  text-decoration: none;
  border-color: var(--primary);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.unit-card__num {
  font-size: 2rem;
  font-weight: 900;
  line-height: 1;
  color: var(--primary);
  opacity: 0.8;
}

.unit-card__body {
  display: flex;
  flex-direction: column;
  flex: 1;
}

.unit-card__title {
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: 0.35rem;
}

.unit-card__sum {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-bottom: 0.85rem;
  line-height: 1.4;
  flex: 1;
}

.unit-card__meta {
  font-size: 0.775rem;
  font-weight: 600;
  color: var(--text-muted);
  margin-bottom: 0.35rem;
}

/* --- Continue Reading Card --- */
.continue {
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: linear-gradient(135deg, var(--primary-soft), var(--bg-elevated));
  border: 1px solid var(--primary);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  margin-bottom: 1.75rem;
  color: inherit;
  box-shadow: var(--shadow);
}

.continue:hover {
  text-decoration: none;
  box-shadow: var(--shadow-lg);
}

.continue__kicker {
  display: block;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  color: var(--primary);
}

.continue__title {
  display: block;
  font-weight: 700;
  font-size: 1.05rem;
}

.continue__meta {
  display: block;
  font-size: 0.825rem;
  color: var(--text-muted);
}

.continue__go {
  padding: 0.4rem 0.85rem;
  background: var(--primary);
  color: #fff;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  white-space: nowrap;
}

/* --- Document List --- */
.doc-list {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  margin-bottom: 2rem;
}

.doc-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
  box-shadow: var(--shadow);
  transition: border-color var(--transition);
}

.doc-row.is-studied {
  border-color: var(--accent);
  background: var(--bg);
}

.doc-row__link {
  display: flex;
  gap: 0.85rem;
  align-items: flex-start;
  color: inherit;
  flex: 1;
}

.doc-row__link:hover {
  text-decoration: none;
}

.doc-row__index {
  font-weight: 800;
  font-size: 0.9rem;
  color: var(--text-muted);
  opacity: 0.6;
}

.doc-row__text {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.doc-row__title {
  font-weight: 700;
  font-size: 1rem;
}

.doc-row__sum {
  font-size: 0.85rem;
  color: var(--text-muted);
}

/* --- Badges & Chips --- */
.badge {
  display: inline-block;
  padding: 0.15rem 0.5rem;
  border-radius: 4px;
  font-size: 0.725rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  width: fit-content;
}

.badge--teoria {
  background: var(--primary-soft);
  color: var(--primary);
}

.badge--repaso {
  background: rgba(234, 179, 8, 0.15);
  color: #b45309;
}

[data-theme="dark"] .badge--repaso {
  color: #fde047;
}

.badge--ejercicio {
  background: rgba(13, 148, 136, 0.15);
  color: var(--accent);
}

.chapter-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.2rem 0.6rem;
  border-radius: 6px;
  font-size: 0.725rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  background: var(--study-soft);
  color: var(--study);
  margin-bottom: 0.4rem;
  border: 1px solid rgba(154, 52, 18, 0.2);
}

.bib-chip {
  display: inline-block;
  font-style: normal;
  padding: 0.1rem 0.45rem;
  border-radius: 4px;
  font-size: 0.825em;
  font-weight: 600;
  background: var(--study-soft);
  color: var(--study);
  border: 1px solid rgba(154, 52, 18, 0.2);
  margin: 0 0.15rem;
}

/* --- Mark Studied Button --- */
.mark-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  background: var(--bg);
  cursor: pointer;
  font-size: 0.825rem;
  font-weight: 600;
  color: var(--text-muted);
  transition: all var(--transition);
  white-space: nowrap;
}

.mark-btn__box {
  width: 14px;
  height: 14px;
  border-radius: 3px;
  border: 2px solid var(--text-muted);
  display: inline-block;
  position: relative;
}

.mark-btn[aria-pressed="true"] {
  border-color: var(--accent);
  color: var(--accent);
  background: rgba(13, 148, 136, 0.1);
}

.mark-btn[aria-pressed="true"] .mark-btn__box {
  border-color: var(--accent);
  background: var(--accent);
}

/* --- Breadcrumb & Pager --- */
.crumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.crumb__sep {
  opacity: 0.5;
}

.pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 2.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

.pager__link {
  display: flex;
  flex-direction: column;
  padding: 0.85rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-elevated);
  color: inherit;
  transition: border-color var(--transition);
}

.pager__link:hover {
  text-decoration: none;
  border-color: var(--primary);
}

.pager__link--next {
  text-align: right;
}

.pager__dir {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  color: var(--primary);
}

.pager__name {
  font-weight: 700;
  font-size: 0.95rem;
}

.pager__unit {
  font-size: 0.8rem;
  color: var(--text-muted);
}

.pager__pos {
  grid-column: 1 / -1;
  text-align: center;
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 0.5rem;
}

/* --- Reader View, TOC & Study Pieces --- */
.lib-reader {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

@media (min-width: 960px) {
  .lib-reader {
    display: grid;
    grid-template-columns: 260px 1fr;
    align-items: start;
    gap: 2rem;
  }
}

/* Mobile-first touch targets and Zen readability */
@media (max-width: 767px) {
  .module-root {
    padding-left: 0.75rem;
    padding-right: 0.75rem;
  }

  .lib-mast h1 {
    font-size: 1.5rem;
  }

  .reader-head {
    padding: 1rem;
    margin-bottom: 1rem;
  }

  .reader-head h1 {
    font-size: 1.45rem;
  }

  .piece {
    padding: 1rem;
    border-radius: var(--radius-sm);
    margin-bottom: 1rem;
  }

  .piece__title {
    font-size: 1.025rem;
  }

  .piece__body, .piece__answer {
    font-size: 1rem;
    line-height: 1.65;
  }

  .mark-btn, .btn, .seg button {
    min-height: 42px;
  }

  .doc-row {
    padding: 0.85rem;
  }

  .reader-tools {
    position: sticky;
    bottom: 0.75rem;
    z-index: 90;
    background: var(--bg-elevated);
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0.65rem 0.85rem;
    margin-top: 1rem;
    justify-content: space-between;
  }
}

.lib-toc {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.85rem 1rem;
  font-size: 0.875rem;
  box-shadow: var(--shadow);
}

.lib-toc summary {
  font-weight: 700;
  cursor: pointer;
  color: var(--text);
  margin-bottom: 0.5rem;
}

.lib-toc nav {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  margin-top: 0.5rem;
}

.lib-toc__link {
  color: var(--text-muted);
  padding: 0.25rem 0.4rem;
  border-radius: 4px;
  line-height: 1.3;
}

.lib-toc__link[data-level="3"] {
  padding-left: 1rem;
  font-size: 0.825rem;
}

.lib-toc__link:hover,
.lib-toc__link.is-active {
  color: var(--primary);
  background: var(--primary-soft);
  text-decoration: none;
}

.reader-head {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  margin-bottom: 1.5rem;
  box-shadow: var(--shadow);
}

.reader-kicker {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
}

.reader-head h1 {
  font-size: 1.65rem;
  font-weight: 800;
  line-height: 1.25;
  margin-bottom: 0.5rem;
}

.reader-sum {
  font-size: 1rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.reader-tools {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.65rem;
  padding-top: 0.85rem;
  border-top: 1px solid var(--border);
}

.seg {
  display: inline-flex;
  background: var(--bg-muted);
  padding: 2px;
  border-radius: var(--radius-sm);
}

.seg button {
  padding: 0.35rem 0.75rem;
  border: none;
  background: transparent;
  font-size: 0.825rem;
  font-weight: 600;
  border-radius: 6px;
  cursor: pointer;
  color: var(--text-muted);
}

.seg button[aria-pressed="true"] {
  background: var(--bg-elevated);
  color: var(--primary);
  box-shadow: var(--shadow);
}

.mode-note {
  font-size: 0.775rem;
  color: var(--text-muted);
  margin-top: 0.5rem;
}

/* --- Study Cards & Groups --- */
.piece {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  margin-bottom: 1.25rem;
  box-shadow: var(--shadow);
  transition: border-color var(--transition);
}

.piece--chapter {
  border-left: 4px solid var(--study);
  background: linear-gradient(180deg, var(--study-soft), var(--bg-elevated) 40px);
}

.piece__bar {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
}

.piece__title {
  font-size: 1.1rem;
  font-weight: 700;
  line-height: 1.35;
}

.piece__toggle {
  flex-shrink: 0;
}

.piece__answer {
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
}

.piece__body p,
.piece__answer p {
  margin-bottom: 0.75rem;
  line-height: 1.6;
}

.piece__body p:last-child,
.piece__answer p:last-child {
  margin-bottom: 0;
}

.piece__body ul,
.piece__answer ul,
.piece__body ol,
.piece__answer ol {
  padding-left: 1.25rem;
  margin-bottom: 0.75rem;
}

.piece__body li,
.piece__answer li {
  margin-bottom: 0.35rem;
  line-height: 1.5;
}

/* Reading mode forces answers visible */
.reader-body.is-reading .piece__answer {
  display: block !important;
}

.reader-body.is-reading .piece__toggle {
  display: none !important;
}

/* --- Math & Formulas --- */
.math-display {
  padding: 0.75rem 1rem;
  margin: 0.85rem 0;
  background: var(--bg-muted);
  border-radius: var(--radius-sm);
  overflow-x: auto;
  font-family: var(--serif);
  font-size: 1.05rem;
  text-align: center;
}

.math-fallback {
  font-family: var(--serif);
  font-weight: 600;
  color: var(--primary);
}