/* ============================================================
   Bit Manipulation Interactive Tutorial — Unified Stylesheet
   All demos and chapter pages share this file.
   ============================================================ */

/* ── CSS variables (light mode) ── */
:root {
  --surface-1: #ffffff;
  --surface-2: #f5f5f3;
  --surface-3: #eeede8;
  --border: rgba(0,0,0,0.15);
  --text-primary: #1a1a18;
  --text-muted: #6b6b67;
  --blue-bg:    #E6F1FB; --blue-text:   #185FA5; --blue-border: #378ADD;
  --green-bg:   #E1F5EE; --green-text:  #0F6E56;
  --red-bg:     #FCEBEB; --red-text:    #A32D2D;
  --amber-bg:   #FAEEDA; --amber-text:  #854F0B;
  --purple-bg:  #EEEDFE; --purple-text: #533AB7;
  --zero-bg:    #EAF3DE; --zero-text:   #27500A; --zero-border: #3B6D11;
}

/* ── CSS variables (dark mode — system preference) ── */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --surface-1: #1e1e1c; --surface-2: #252523; --surface-3: #2e2e2b;
    --border: rgba(255,255,255,0.12);
    --text-primary: #e8e6de; --text-muted: #9c9a92;
    --blue-bg:    #042C53; --blue-text:   #B5D4F4; --blue-border: #185FA5;
    --green-bg:   #04342C; --green-text:  #9FE1CB;
    --red-bg:     #501313; --red-text:    #F7C1C1;
    --amber-bg:   #412402; --amber-text:  #FAC775;
    --purple-bg:  #26215C; --purple-text: #CECBF6;
    --zero-bg:    #173404; --zero-text:   #C0DD97; --zero-border: #639922;
  }
}

/* ── CSS variables (dark mode — manual override) ── */
[data-theme="dark"] {
  --surface-1: #1e1e1c; --surface-2: #252523; --surface-3: #2e2e2b;
  --border: rgba(255,255,255,0.12);
  --text-primary: #e8e6de; --text-muted: #9c9a92;
  --blue-bg:    #042C53; --blue-text:   #B5D4F4; --blue-border: #185FA5;
  --green-bg:   #04342C; --green-text:  #9FE1CB;
  --red-bg:     #501313; --red-text:    #F7C1C1;
  --amber-bg:   #412402; --amber-text:  #FAC775;
  --purple-bg:  #26215C; --purple-text: #CECBF6;
  --zero-bg:    #173404; --zero-text:   #C0DD97; --zero-border: #639922;
}

/* ── Reset / base ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--surface-1);
  color: var(--text-primary);
  padding: 2rem 1rem;
  line-height: 1.6;
}

/* ── Navigation bar ── */
.navbar {
  max-width: 680px;
  margin: 0 auto 2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.75rem 0;
  border-bottom: 0.5px solid var(--border);
}
.navbar-brand {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text-primary);
  text-decoration: none;
}
.navbar-nav {
  display: flex;
  gap: 1rem;
  align-items: center;
}
.navbar-nav a {
  font-size: 0.875rem;
  color: var(--blue-text);
  text-decoration: none;
}
.navbar-nav a:hover { text-decoration: underline; }

.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 30px;
  height: 30px;
  border-radius: 8px;
  border: 0.5px solid var(--border);
  background: var(--surface-2);
  color: var(--text-muted);
  cursor: pointer;
  transition: background 0.1s, border-color 0.1s, color 0.1s;
  padding: 0;
}
.theme-toggle:hover {
  background: var(--blue-bg);
  border-color: var(--blue-border);
  color: var(--blue-text);
}

/* ── Page chrome ── */
.page-header {
  max-width: 680px;
  margin: 0 auto 2rem;
}
.page-header h1 {
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: 0.25rem;
}
.page-header p {
  font-size: 0.9rem;
  color: var(--text-muted);
}
.chapter-label {
  display: inline-block;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--blue-text);
  background: var(--blue-bg);
  border-radius: 5px;
  padding: 2px 8px;
  margin-bottom: 0.6rem;
}

/* ── Prose ── */
.prose {
  max-width: 680px;
  margin: 0 auto;
}
.prose p {
  font-size: 0.95rem;
  color: var(--text-primary);
  margin-bottom: 1rem;
}
.prose ul, .prose ol {
  margin-bottom: 1rem;
  padding-left: 1.5rem;
}
.prose li {
  margin-bottom: 0.25rem;
  font-size: 0.95rem;
  color: var(--text-primary);
  line-height: 1.7;
}
.prose code {
  font-family: monospace;
  font-size: 0.88em;
  background: var(--surface-3);
  border-radius: 4px;
  padding: 1px 5px;
}
.prose pre {
  background: var(--surface-3);
  border-radius: 6px;
  padding: 10px 14px;
  overflow-x: auto;
  font-size: 0.88em;
  line-height: 1.7;
  margin-bottom: 1rem;
}
.prose pre code {
  background: none;
  padding: 0;
  font-size: inherit;
}

/* ── Chapter goals box ── */
.chapter-goals {
  border-left: 3px solid var(--blue-border);
  background: var(--blue-bg);
  border-radius: 0 8px 8px 0;
  padding: 12px 16px;
  margin-bottom: 1.5rem;
  font-size: 0.9rem;
  color: var(--text-primary);
  line-height: 1.7;
}
.chapter-goals-label {
  display: block;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--blue-text);
  margin-bottom: 4px;
}

/* ── Demo box ── */
.demo-box {
  background: var(--surface-2);
  border-radius: 12px;
  border: 0.5px solid var(--border);
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
}
.demo-title {
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

/* ── Formula bar ── */
.formula-bar {
  font-family: monospace;
  font-size: 13px;
  background: var(--surface-1);
  border: 0.5px solid var(--border);
  border-radius: 8px;
  padding: 8px 12px;
  margin-bottom: 14px;
  color: var(--text-primary);
  overflow-x: auto;
  white-space: nowrap;
}

/* ── Bit rows ── */
.bit-row {
  display: flex;
  gap: 3px;
  flex-wrap: wrap;
}
.bit-index-row {
  display: flex;
  gap: 3px;
  flex-wrap: wrap;
  margin-bottom: 4px;
}
.bit-index {
  width: 30px;
  text-align: center;
  font-size: 10px;
  color: var(--text-muted);
  font-family: monospace;
}

/* ── Bit boxes ── */
.bit {
  width: 30px;
  height: 30px;
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: monospace;
  font-size: 13px;
  font-weight: 500;
  transition: background 0.13s, color 0.13s;
  user-select: none;
}
.bit.clickable { cursor: pointer; }
.bit.b-1     { background: #185FA5; color: #E6F1FB; }
.bit.b-0     { background: var(--surface-3); color: var(--text-muted); }
.bit.b-sign  { background: #A32D2D; color: #FCEBEB; }
.bit.b-exp   { background: #533AB7; color: #EEEDFE; }
.bit.b-mant  { background: #0F6E56; color: #E1F5EE; }
.bit.b-pass  { background: #0F6E56; color: #E1F5EE; }
.bit.b-block { background: var(--surface-3); color: var(--text-muted); opacity: 0.4; }
.bit.b-set   { background: #533AB7; color: #EEEDFE; }
.bit.b-clear { background: #A32D2D; color: #FCEBEB; }
.bit.b-flip  { background: #9F3BAA; color: #F4C0D1; }
.bit.b-target{ background: #854F0B; color: #FAEEDA; }
.bit.b-mask-1{ background: #3B6D11; color: #EAF3DE; }
.bit.b-mask-0{ background: #633806; color: #FAEEDA; }

/* ── Tabs ── */
.tab-row {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 1.25rem;
}
.tab {
  padding: 6px 14px;
  border-radius: 8px;
  border: 0.5px solid var(--border);
  font-size: 13px;
  cursor: pointer;
  background: var(--surface-2);
  color: var(--text-muted);
  transition: background 0.1s, border-color 0.1s, color 0.1s;
}
.tab.active {
  border-color: var(--blue-border);
  background: var(--blue-bg);
  color: var(--blue-text);
}

/* ── Place value labels ── */
.place-row, .contrib-row {
  display: flex;
  gap: 3px;
  flex-wrap: wrap;
}
.place-cell, .contrib-cell {
  width: 30px;
  text-align: center;
  font-family: monospace;
  line-height: 1.2;
}
.place-cell {
  font-size: 9px;
  color: var(--text-muted);
  margin-bottom: 3px;
}
.place-cell .power  { display: block; }
.place-cell .pvalue { display: block; font-size: 10px; color: var(--blue-text); font-weight: 600; }
.contrib-cell {
  font-size: 10px;
  font-weight: 600;
  color: var(--blue-text);
  height: 16px;
  margin-top: 3px;
}
.contrib-cell.zero { color: transparent; }

/* ── Result box ── */
.result-box {
  border-top: 0.5px solid var(--border);
  margin-top: 14px;
  padding-top: 12px;
}
.result-value {
  font-size: 28px;
  font-weight: 600;
  font-family: monospace;
  color: var(--blue-text);
}
.result-label {
  font-size: 12px;
  color: var(--text-muted);
  margin-left: 6px;
  font-family: monospace;
}
.result-explain {
  font-size: 13px;
  color: var(--text-muted);
  line-height: 1.7;
  margin-top: 6px;
}
.result-explain .term-active {
  color: var(--blue-text);
  font-family: monospace;
  font-weight: 500;
}

/* ── Presets ── */
.preset-row {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin-bottom: 1rem;
  align-items: center;
}
.preset-label {
  font-size: 12px;
  color: var(--text-muted);
  margin-right: 2px;
}
.preset-btn {
  padding: 4px 10px;
  border-radius: 6px;
  border: 0.5px solid var(--border);
  font-size: 12px;
  font-family: monospace;
  cursor: pointer;
  background: var(--surface-1);
  color: var(--text-primary);
  transition: background 0.1s, border-color 0.1s;
}
.preset-btn:hover {
  background: var(--blue-bg);
  color: var(--blue-text);
  border-color: var(--blue-border);
}

/* ── Analogy panel ── */
.analogy-panel {
  background: var(--surface-1);
  border: 0.5px solid var(--border);
  border-radius: 8px;
  padding: 12px 14px;
  margin-top: 14px;
  font-size: 13px;
  color: var(--text-muted);
}
.analogy-panel strong { color: var(--text-primary); }
.analogy-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 8px;
  margin-top: 8px;
}
.analogy-col {
  background: var(--surface-2);
  border-radius: 6px;
  padding: 8px 10px;
  font-family: monospace;
  font-size: 12px;
  line-height: 1.8;
}
.analogy-col .col-head {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  margin-bottom: 4px;
  font-family: sans-serif;
}

/* ── Chapter list (index.html) ── */
.chapter-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin: 1.5rem 0;
}
.chapter-card {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  background: var(--surface-2);
  border: 0.5px solid var(--border);
  border-radius: 10px;
  text-decoration: none;
  color: var(--text-primary);
  transition: border-color 0.1s, background 0.1s;
}
.chapter-card:hover {
  border-color: var(--blue-border);
  background: var(--blue-bg);
}
.chapter-card-num {
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--blue-text);
  min-width: 72px;
  flex-shrink: 0;
}
.chapter-card-body {
  display: flex;
  flex-direction: column;
  flex: 1;
  min-width: 0;
}
.chapter-card-title {
  font-size: 0.95rem;
  font-weight: 600;
}
.chapter-card-desc {
  font-size: 0.875rem;
  color: var(--text-muted);
}
.chapter-card-badge {
  margin-left: auto;
  flex-shrink: 0;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.04em;
  padding: 2px 8px;
  border-radius: 5px;
  background: var(--amber-bg);
  color: var(--amber-text);
}
.chapter-card--wip {
  opacity: 0.6;
  cursor: default;
}
.chapter-card--wip:hover {
  border-color: var(--border);
  background: var(--surface-2);
}
.chapter-section-label {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin: 6px 0 2px;
}
.chapter-section-label::before,
.chapter-section-label::after {
  content: '';
  flex: 1;
  height: 0.5px;
  background: var(--border);
}

/* ── Metric cards (clock info panel, log₂ demo) ── */
.metric-row {
  display: flex;
  gap: 8px;
  margin: 10px 0 8px;
}
.metric {
  flex: 1;
  background: var(--surface-1);
  border: 0.5px solid var(--border);
  border-radius: 8px;
  padding: 10px 14px;
  text-align: center;
}
.metric-label {
  font-size: 11px;
  color: var(--text-muted);
  margin-bottom: 4px;
}
.metric-value {
  font-size: 22px;
  font-weight: 500;
  font-family: monospace;
  color: var(--text-primary);
}

/* ── Step-advance button (demo stepper) ── */
.step-btn {
  padding: 6px 14px;
  border-radius: 8px;
  border: 0.5px solid var(--blue-border);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  background: var(--blue-bg);
  color: var(--blue-text);
  transition: background 0.1s, color 0.1s;
  margin-top: 10px;
}
.step-btn:hover {
  background: var(--blue-text);
  color: var(--surface-1);
}

/* ── Labeled operation rows (operators / negation demos) ── */
.op-grid {
  display: flex;
  flex-direction: column;
  gap: 6px;
  margin-bottom: 10px;
}
.op-row {
  display: flex;
  align-items: center;
  gap: 8px;
}
.op-label {
  width: 52px;
  font-family: monospace;
  font-size: 12px;
  color: var(--text-muted);
  text-align: right;
  flex-shrink: 0;
}
.op-value {
  font-family: monospace;
  font-size: 12px;
  color: var(--text-muted);
  margin-left: 6px;
  min-width: 36px;
}
.op-divider {
  height: 0;
  border-top: 0.5px solid var(--border);
  margin: 4px 0 4px 60px;
}

/* ── About page links box ── */
.about-links {
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.about-link {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.9rem;
  color: var(--blue-text);
  text-decoration: none;
}
.about-link:hover { text-decoration: underline; }
.about-link svg { flex-shrink: 0; color: var(--text-muted); }

/* ── Collapsible aside ── */
.collapsible {
  border: 0.5px solid var(--border);
  border-radius: 8px;
  margin: 1rem 0;
  font-size: 13px;
  color: var(--text-muted);
}
.collapsible summary {
  cursor: pointer;
  user-select: none;
  padding: 10px 14px;
  list-style: none;
  display: flex;
  align-items: center;
  gap: 8px;
}
.collapsible summary::-webkit-details-marker { display: none; }
.collapsible summary::before {
  content: '▸';
  font-size: 10px;
  flex-shrink: 0;
  transition: transform 0.15s;
}
details[open].collapsible summary::before { transform: rotate(90deg); }
.collapsible-body {
  padding: 0 14px 12px;
  border-top: 0.5px solid var(--border);
}
.collapsible-body > *:first-child { margin-top: 10px; }
.collapsible-body > *:last-child  { margin-bottom: 0; }
.collapsible-body p { line-height: 1.7; }

/* ── Responsive ── */
@media (max-width: 480px) {
  .bit, .bit-index, .place-cell, .contrib-cell { width: 24px; }
  .bit { height: 24px; font-size: 11px; }
}