:root {
  --bg: #F7F5F0;
  --bg-dim: #EDEAE3;
  --card-bg: #FFFFFF;
  --ink: #1A1E23;
  --ink-soft: #5A6069;
  --ink-muted: #8B9099;
  --rule: #D5D2CA;
  --topo: #2B6E4E;
  --topo-deep: #1B4A33;
  --topo-light: #E8F3ED;
  --sidebar-bg: #1E2A30;
  --sidebar-text: #D9E2E6;
  --sidebar-muted: #8DA1AB;
  --accent: #C4582A;
  --accent-light: #FFF2EC;
  --display: 'Newsreader', Georgia, serif;
  --body: 'Inter', system-ui, sans-serif;
  --mono: 'JetBrains Mono', 'Consolas', monospace;
}
*, *::before, *::after { box-sizing: border-box; }
html, body { margin: 0; padding: 0; height: 100%; }
body { font-family: var(--body); color: var(--ink); background: var(--bg); font-size: 14px; line-height: 1.5; }
a { color: var(--topo); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ── Layout ── */
.app { display: grid; grid-template-columns: 300px 1fr; min-height: 100vh; }

/* ── Sidebar ── */
.sidebar {
  background: var(--sidebar-bg);
  color: var(--sidebar-text);
  padding: 24px 18px 16px;
  position: sticky; top: 0; height: 100vh;
  overflow-y: auto;
  display: flex; flex-direction: column;
  border-right: 4px solid var(--topo-deep);
}
.sidebar-head { margin-bottom: 16px; }
.sidebar-badge {
  display: inline-block;
  font-family: var(--mono); font-size: 10px; letter-spacing: 2px;
  color: var(--topo-deep); background: var(--topo-light);
  padding: 2px 8px; border-radius: 2px; font-weight: 600; margin-bottom: 8px;
}
.sidebar-head h1 {
  font-family: var(--display); font-size: 24px; line-height: 1.15;
  margin: 0 0 4px; font-weight: 600; color: #F0EDE6;
}
.sidebar-head h1 a { color: inherit; text-decoration: none; }
.sidebar-head h1 span { display: block; font-size: 16px; font-weight: 400; color: var(--sidebar-muted); margin-top: 2px; }
.sidebar-sub { font-size: 11px; color: var(--sidebar-muted); border-top: 1px solid rgba(255,255,255,.1); padding-top: 8px; margin-top: 10px; font-style: italic; }
.sidebar-search { margin-bottom: 12px; }
.sidebar-search input {
  width: 100%; padding: 8px 10px; border-radius: 4px;
  border: 1px solid rgba(255,255,255,.15); background: rgba(0,0,0,.2);
  color: #F0EDE6; font-family: var(--body); font-size: 13px;
}
.sidebar-search input::placeholder { color: var(--sidebar-muted); }
.sidebar-search input:focus { outline: 2px solid var(--topo); outline-offset: 1px; }
.sidebar-index { flex: 1; overflow-y: auto; }
.ch-entry {
  display: flex; align-items: baseline; gap: 8px;
  padding: 7px 8px; border-radius: 4px; cursor: pointer;
  border-left: 3px solid transparent;
  transition: background .1s, border-color .1s; margin-bottom: 1px;
  color: var(--sidebar-text); text-decoration: none;
}
.ch-entry:hover { background: rgba(255,255,255,.06); text-decoration: none; }
.ch-entry.active { background: rgba(255,255,255,.1); border-left-color: var(--topo); }
.ch-num { font-family: var(--mono); font-size: 11px; color: var(--topo); min-width: 20px; font-weight: 600; }
.ch-title-text { font-size: 12.5px; line-height: 1.35; flex: 1; }
.ch-count { font-family: var(--mono); font-size: 10px; color: var(--sidebar-muted); white-space: nowrap; }
.sidebar-foot {
  border-top: 1px solid rgba(255,255,255,.1); padding-top: 8px; margin-top: 8px;
  font-family: var(--mono); font-size: 10.5px; color: var(--sidebar-muted);
  display: flex; justify-content: space-between; align-items: center;
}
.sidebar-user a { color: var(--sidebar-muted); }

/* ── Main ── */
.main-panel { padding: 36px 48px 80px; max-width: 960px; }

/* ── Flash messages ── */
.flash-container { margin-bottom: 16px; }
.flash { padding: 10px 14px; border-radius: 4px; font-size: 13px; margin-bottom: 6px; }
.flash-error { background: #FDECEA; color: #A01A3A; border: 1px solid #F5C6CB; }
.flash-success { background: var(--topo-light); color: var(--topo-deep); border: 1px solid #B8DBC8; }
.flash-info { background: #E1ECF5; color: #2A5F8A; border: 1px solid #B8D4F0; }

/* ── Chapter header ── */
.ch-header { margin-bottom: 20px; padding-bottom: 16px; border-bottom: 2px solid var(--rule); }
.ch-eyebrow { font-family: var(--mono); font-size: 11px; letter-spacing: 1.5px; color: var(--topo); text-transform: uppercase; margin-bottom: 6px; }
.ch-header h2 { font-family: var(--display); font-size: 32px; margin: 0; line-height: 1.15; font-weight: 600; }

/* ── Tabs ── */
.tabs { display: flex; gap: 2px; margin-bottom: 24px; border-bottom: 1px solid var(--rule); overflow-x: auto; }
.tab-btn {
  font-family: var(--mono); font-size: 11px; letter-spacing: .3px; text-transform: uppercase;
  padding: 9px 14px; background: none; border: none; cursor: pointer;
  color: var(--ink-soft); border-bottom: 2px solid transparent; margin-bottom: -1px; white-space: nowrap;
  text-decoration: none;
}
.tab-btn:hover { color: var(--ink); text-decoration: none; }
.tab-btn.active { color: var(--topo-deep); border-bottom-color: var(--topo); font-weight: 600; }

.empty-state { font-family: var(--mono); font-size: 12px; color: var(--ink-muted); padding: 40px 0; text-align: center; }

/* ── Knowledge Map ── */
.knowledge-map { background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; padding: 24px; overflow-x: auto; }
.knowledge-map pre { font-family: var(--mono); font-size: 12px; line-height: 1.6; color: var(--ink); margin: 0; white-space: pre; }

/* ── Objectives ── */
.obj-group { margin-bottom: 20px; }
.obj-group h3 { font-family: var(--mono); font-size: 12px; letter-spacing: 1px; text-transform: uppercase; color: var(--topo); margin: 0 0 8px; padding-bottom: 6px; border-bottom: 1px solid var(--bg-dim); }
.obj-group ul { margin: 0; padding-left: 20px; }
.obj-group li { font-size: 13.5px; line-height: 1.6; margin-bottom: 4px; }

/* ── Equations ── */
.eq-card { background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; padding: 18px 22px; margin-bottom: 16px; }
.eq-card h4 { font-family: var(--mono); font-size: 12px; color: var(--topo); margin: 0 0 10px; text-transform: uppercase; letter-spacing: .5px; }
.eq-card .eq-content { font-size: 13.5px; line-height: 1.7; }
.eq-card .eq-content p { margin: 4px 0; }
.eq-block { margin: 10px 0; text-align: center; font-size: 16px; }

/* ── Checklist ── */
.checklist-item { display: flex; align-items: flex-start; gap: 8px; padding: 6px 0; font-size: 13.5px; line-height: 1.5; border-bottom: 1px solid var(--bg-dim); }
.checklist-item input[type="checkbox"] { margin-top: 3px; accent-color: var(--topo); cursor: pointer; flex-shrink: 0; }

/* ── Stats ── */
.stats-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 10px; }
.stat-cell { display: flex; justify-content: space-between; padding: 10px 14px; background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; font-size: 13px; }
.stat-label { color: var(--ink-soft); }
.stat-val { font-family: var(--mono); font-weight: 600; color: var(--topo-deep); }

/* ── Connections ── */
.conn-section-title { font-family: var(--mono); font-size: 12px; color: var(--ink-soft); margin: 20px 0 8px; text-transform: uppercase; letter-spacing: 1px; }
.conn-table { width: 100%; border-collapse: collapse; font-size: 13px; margin-bottom: 20px; }
.conn-table th { font-family: var(--mono); font-size: 11px; text-transform: uppercase; letter-spacing: .5px; color: var(--topo); text-align: left; padding: 8px 12px; border-bottom: 2px solid var(--rule); }
.conn-table td { padding: 8px 12px; border-bottom: 1px solid var(--bg-dim); vertical-align: top; }
.conn-table tr:hover td { background: var(--topo-light); }

/* ── Visual Recs ── */
.vis-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.vis-card { background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; padding: 14px 16px; }
.vis-concept { font-weight: 600; font-size: 13px; margin-bottom: 4px; }
.vis-desc { font-size: 12.5px; color: var(--ink-soft); line-height: 1.5; }

/* ── Flashcard deck ── */
.deck-toolbar { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; margin-bottom: 20px; }
.filter-select { font-family: var(--body); font-size: 12.5px; padding: 6px 10px; border: 1px solid var(--rule); border-radius: 4px; background: var(--card-bg); color: var(--ink); }
.chip { font-family: var(--mono); font-size: 11px; padding: 6px 12px; border-radius: 16px; border: 1px solid var(--ink-soft); background: transparent; color: var(--ink-soft); cursor: pointer; }
.chip:hover { background: var(--ink); color: var(--bg); border-color: var(--ink); }
.chip.primary { background: var(--topo); color: #fff; border-color: var(--topo); }
.chip.primary:hover { background: var(--topo-deep); }
.deck-progress { font-family: var(--mono); font-size: 11.5px; color: var(--ink-soft); margin-left: auto; }
.card-stage { display: flex; flex-direction: column; align-items: center; gap: 14px; }

.index-card { width: 100%; max-width: 720px; min-height: 380px; perspective: 1200px; cursor: pointer; }
.index-card-inner { position: relative; width: 100%; height: 100%; min-height: 380px; transition: transform .45s cubic-bezier(.4,.2,.2,1); transform-style: preserve-3d; }
.index-card.flipped .index-card-inner { transform: rotateY(180deg); }
.card-face { position: absolute; inset: 0; backface-visibility: hidden; background: var(--card-bg); border: 1px solid var(--rule); border-radius: 6px; box-shadow: 0 6px 20px rgba(0,0,0,.08), 0 1px 0 var(--rule); padding: 28px 28px 20px; display: flex; flex-direction: column; }
.card-face.back { transform: rotateY(180deg); background: #FAFAF5; }
.card-face-label { font-family: var(--mono); font-size: 10px; letter-spacing: 1.5px; text-transform: uppercase; color: var(--topo); margin-bottom: 14px; }
.card-divider { height: 1px; background: var(--rule); margin-bottom: 14px; }
.card-text { font-size: 17px; line-height: 1.65; flex: 1; overflow-y: auto; }
.card-face.front .card-text { font-family: var(--display); font-size: 19px; }
.card-extra { margin-top: 12px; padding-top: 10px; border-top: 1px dashed var(--rule); font-size: 13px; color: var(--ink-soft); line-height: 1.55; font-style: italic; }
.card-meta { margin-top: auto; padding-top: 12px; display: flex; gap: 8px; flex-wrap: wrap; }
.meta-pill { font-family: var(--mono); font-size: 10px; padding: 3px 8px; border-radius: 10px; background: var(--bg-dim); color: var(--ink-soft); }
.meta-pill.difficulty-Basic { background: #E3F0E8; color: #1B6B3A; }
.meta-pill.difficulty-Intermediate { background: #E1ECF5; color: #2A5F8A; }
.meta-pill.difficulty-Advanced { background: #FFF3E0; color: #B35C00; }
.meta-pill.difficulty-Expert { background: #FCE4EC; color: #A01A3A; }
.card-controls { display: flex; align-items: center; gap: 12px; }
.nav-btn { font-family: var(--mono); font-size: 18px; width: 38px; height: 38px; border-radius: 50%; border: 1px solid var(--rule); background: var(--card-bg); color: var(--ink); cursor: pointer; display: flex; align-items: center; justify-content: center; }
.nav-btn:hover { background: var(--ink); color: var(--bg); }
.nav-btn:disabled { opacity: .25; cursor: default; }
.nav-btn:disabled:hover { background: var(--card-bg); color: var(--ink); }
.flip-hint { font-family: var(--mono); font-size: 11px; color: var(--ink-muted); }

/* ── Search ── */
.search-results h2 { font-family: var(--display); font-size: 24px; margin: 0 0 16px; }
.search-hit { display: block; background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; padding: 14px 18px; margin-bottom: 10px; color: var(--ink); text-decoration: none; }
.search-hit:hover { border-color: var(--topo); text-decoration: none; }
.hit-chapter { font-family: var(--mono); font-size: 10px; color: var(--topo); text-transform: uppercase; letter-spacing: 1px; margin-bottom: 4px; }
.hit-front { font-family: var(--display); font-size: 15px; margin-bottom: 4px; }
.hit-back { font-size: 13px; color: var(--ink-soft); line-height: 1.5; }
.hit-meta { margin-top: 6px; display: flex; gap: 6px; }

/* ── Welcome ── */
.welcome { max-width: 66ch; }
.welcome h2 { font-family: var(--display); font-size: 38px; margin: 0 0 12px; line-height: 1.1; }
.welcome p { font-size: 15px; line-height: 1.7; margin: 0 0 14px; }
.stat-row { display: flex; gap: 28px; margin-top: 10px; }
.stat-block .num { font-family: var(--mono); font-size: 32px; color: var(--topo); display: block; font-weight: 700; }
.stat-block .label { font-family: var(--mono); font-size: 10px; letter-spacing: 1px; text-transform: uppercase; color: var(--ink-soft); }

/* ── Auth pages ── */
.auth-page { display: flex; align-items: center; justify-content: center; min-height: 100vh; background: var(--bg); }
.auth-card { background: var(--card-bg); border: 1px solid var(--rule); border-radius: 6px; padding: 40px 36px; width: 100%; max-width: 400px; box-shadow: 0 8px 30px rgba(0,0,0,.08); }
.auth-card .auth-badge { font-family: var(--mono); font-size: 10px; letter-spacing: 2px; color: var(--topo-deep); background: var(--topo-light); padding: 2px 8px; border-radius: 2px; font-weight: 600; display: inline-block; margin-bottom: 12px; }
.auth-card h1 { font-family: var(--display); font-size: 28px; margin: 0 0 20px; line-height: 1.2; }
.auth-card h1 span { font-size: 18px; font-weight: 400; color: var(--ink-soft); }
.auth-card label { display: block; font-family: var(--mono); font-size: 11px; letter-spacing: .5px; text-transform: uppercase; color: var(--ink-soft); margin: 14px 0 4px; }
.auth-card input[type="text"], .auth-card input[type="email"], .auth-card input[type="password"] {
  width: 100%; padding: 10px 12px; border: 1px solid var(--rule); border-radius: 4px;
  font-family: var(--body); font-size: 14px; background: var(--bg);
}
.auth-card input:focus { outline: 2px solid var(--topo); outline-offset: 1px; }
.auth-btn { width: 100%; padding: 12px; margin-top: 20px; background: var(--topo); color: #fff; border: none; border-radius: 4px; font-family: var(--body); font-size: 14px; font-weight: 600; cursor: pointer; }
.auth-btn:hover { background: var(--topo-deep); }
.auth-alt { text-align: center; margin-top: 16px; font-size: 13px; color: var(--ink-soft); }

/* ── Annotations ── */
.annotations-panel h3 { font-family: var(--mono); font-size: 13px; color: var(--ink-soft); margin: 0 0 16px; text-transform: uppercase; letter-spacing: 1px; }
.ann-section { margin-bottom: 24px; }
.ann-section h4 { font-family: var(--mono); font-size: 11px; color: var(--topo); text-transform: uppercase; letter-spacing: 1px; margin: 0 0 8px; border-bottom: 1px solid var(--bg-dim); padding-bottom: 6px; }
.ann-item { background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; padding: 10px 14px; margin-bottom: 8px; display: flex; align-items: flex-start; gap: 10px; }
.ann-content { flex: 1; font-size: 13.5px; line-height: 1.6; white-space: pre-wrap; }
.ann-meta { font-family: var(--mono); font-size: 10px; color: var(--ink-muted); display: flex; align-items: center; gap: 6px; }
.ann-delete { background: none; border: none; color: var(--accent); cursor: pointer; font-size: 16px; padding: 0 4px; }
.ann-delete:hover { color: #A01A3A; }
.inline-form { display: inline; }
.ann-images-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(160px, 1fr)); gap: 12px; }
.ann-image-item { background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; padding: 8px; position: relative; }
.ann-image-item img { width: 100%; height: auto; border-radius: 3px; display: block; }
.ann-img-caption { font-size: 11px; color: var(--ink-soft); margin-top: 4px; }
.ann-image-item .ann-delete { position: absolute; top: 4px; right: 4px; background: rgba(255,255,255,.9); border-radius: 50%; width: 22px; height: 22px; display: flex; align-items: center; justify-content: center; }

.ann-forms { display: flex; flex-direction: column; gap: 10px; margin-top: 20px; }
.ann-add { background: var(--card-bg); border: 1px solid var(--rule); border-radius: 4px; padding: 12px 16px; }
.ann-add summary { font-family: var(--mono); font-size: 12px; color: var(--topo); cursor: pointer; text-transform: uppercase; letter-spacing: .5px; }
.ann-add form { margin-top: 10px; display: flex; flex-direction: column; gap: 8px; }
.ann-add textarea, .ann-add input[type="url"], .ann-add input[type="text"] {
  width: 100%; padding: 8px 10px; border: 1px solid var(--rule); border-radius: 4px;
  font-family: var(--body); font-size: 13px; background: var(--bg);
}
.ann-add textarea:focus, .ann-add input:focus { outline: 2px solid var(--topo); outline-offset: 1px; }
.ann-add input[type="file"] { font-size: 13px; }

/* Card annotations (below flashcard) */
.card-annotations { max-width: 620px; margin: 20px auto 0; width: 100%; }
.ann-heading { font-family: var(--mono); font-size: 12px; color: var(--ink-soft); text-transform: uppercase; letter-spacing: 1px; margin: 0 0 10px; }

/* ── Multi-book sidebar ── */
.sidebar-home-link { color: inherit; text-decoration: none; }
.sidebar-home-link:hover { text-decoration: none; }
.sidebar-book-head {
  padding: 10px 8px 6px;
  border-left: 3px solid var(--topo);
  margin-top: 6px;
  margin-bottom: 2px;
}
.sidebar-book-head:first-child { margin-top: 0; }
.sidebar-book-head a {
  font-family: var(--mono); font-size: 11.5px; font-weight: 600;
  color: var(--sidebar-text); text-decoration: none; text-transform: uppercase; letter-spacing: .5px;
}
.sidebar-book-head a:hover { text-decoration: underline; }
.sidebar-book-head .sidebar-book-meta { display: block; font-size: 10px; color: var(--sidebar-muted); margin-top: 2px; }
.sidebar-book-head.active { background: rgba(255,255,255,.04); }
.ch-entry { border-left-color: var(--accent, var(--topo)); }
.ch-entry.active { border-left-color: var(--accent, var(--topo)); }

/* ── Book landing page ── */
.book-landing { max-width: 70ch; }
.book-header { margin-bottom: 20px; padding-bottom: 16px; border-bottom: 2px solid var(--rule); }
.book-chapter-grid { display: grid; grid-template-columns: 1fr; gap: 8px; margin-top: 20px; }
.book-ch-card {
  display: flex; align-items: baseline; gap: 12px;
  background: var(--card-bg); border: 1px solid var(--rule); border-left: 3px solid var(--accent, var(--topo));
  border-radius: 4px; padding: 12px 16px; text-decoration: none; color: var(--ink);
  transition: border-color .1s, box-shadow .1s;
}
.book-ch-card:hover { border-color: var(--accent, var(--topo)); box-shadow: 0 2px 8px rgba(0,0,0,.06); text-decoration: none; }
.book-ch-num { font-family: var(--mono); font-size: 13px; font-weight: 600; color: var(--accent, var(--topo)); min-width: 22px; }
.book-ch-title { flex: 1; font-size: 14px; }
.book-ch-count { font-family: var(--mono); font-size: 11px; color: var(--ink-muted); }

/* ── Welcome book cards ── */
.welcome-books { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin-top: 20px; }
.welcome-book-card {
  background: var(--card-bg); border: 1px solid var(--rule); border-radius: 6px;
  padding: 24px; text-decoration: none; color: var(--ink);
  border-top: 4px solid var(--accent, var(--topo));
  transition: box-shadow .15s;
}
.welcome-book-card:hover { box-shadow: 0 4px 16px rgba(0,0,0,.08); text-decoration: none; }
.wbc-badge { display: inline-block; font-family: var(--mono); font-size: 10px; letter-spacing: 2px; color: #fff; padding: 3px 10px; border-radius: 3px; margin-bottom: 10px; }
.welcome-book-card h3 { font-family: var(--display); font-size: 20px; margin: 0 0 6px; line-height: 1.2; }
.wbc-authors { font-size: 13px; color: var(--ink-soft); margin: 0 0 2px; }
.wbc-edition { font-size: 12px; color: var(--ink-muted); margin: 0 0 12px; font-style: italic; }
.wbc-stats { font-family: var(--mono); font-size: 11px; color: var(--ink-soft); display: flex; gap: 16px; }

/* ── Tab accent color ── */
.tab-btn.active { color: var(--tab-accent, var(--topo-deep)); border-bottom-color: var(--tab-accent, var(--topo)); }

@media (max-width: 860px) {
  .app { grid-template-columns: 1fr; }
  .sidebar { position: relative; height: auto; max-height: 60vh; }
  .main-panel { padding: 20px 16px 60px; }
  .vis-grid { grid-template-columns: 1fr; }
  .ch-header h2 { font-size: 24px; }
}