/* ==========================================================================
   Python Execution Simulator - Common Stylesheet (css/style.css)
   Designed for interactive step-by-step visualization across all chapters
   ========================================================================== */

:root {
  --bg-body: #0f172a;
  --bg-surface: #1e293b;
  --bg-surface-elevated: #26334d;
  --bg-card: #162032;
  --bg-code: #0b1120;
  --bg-terminal: #090d16;
  --border-color: #334155;
  --border-highlight: #38bdf8;

  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;

  --accent-blue: #38bdf8;
  --accent-indigo: #818cf8;
  --accent-emerald: #34d399;
  --accent-amber: #fbbf24;
  --accent-rose: #fb7185;
  --accent-purple: #c084fc;

  --syntax-keyword: #ff7b72;
  --syntax-func: #d2a8ff;
  --syntax-string: #a5d6ff;
  --syntax-number: #79c0ff;
  --syntax-comment: #8b949e;
  --syntax-op: #ffa657;
  --syntax-var: #ffa657;

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --shadow-md: 0 10px 25px -5px rgba(0, 0, 0, 0.4), 0 8px 10px -6px rgba(0, 0, 0, 0.3);
  --font-sans: 'Pretendard', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Noto Sans KR', 'Noto Sans JP', 'Noto Sans SC', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'SFMono-Regular', Consolas, 'Liberation Mono', Menlo, monospace;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  background-color: var(--bg-body);
  color: var(--text-primary);
  font-family: var(--font-sans);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Header & Navigation */
.sim-header {
  background: rgba(15, 23, 42, 0.92);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
  padding: 0.75rem 1.5rem;
}

.header-top {
  max-width: 1440px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
}

.brand-area {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.chapter-badge {
  background: linear-gradient(135deg, #0284c7, #4f46e5);
  color: #fff;
  font-weight: 700;
  font-size: 0.8rem;
  padding: 0.25rem 0.65rem;
  border-radius: 999px;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  box-shadow: 0 2px 8px rgba(56, 189, 248, 0.3);
}

.sim-title-group h1 {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.sim-title-group p {
  font-size: 0.82rem;
  color: var(--text-muted);
}

/* File Switcher Navigation */
.file-nav {
  max-width: 1440px;
  margin: 0.65rem auto 0;
  padding-top: 0.6rem;
  border-top: 1px solid rgba(51, 65, 85, 0.6);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  overflow-x: auto;
}

.file-nav-label {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-right: 0.25rem;
  white-space: nowrap;
}

.file-link {
  text-decoration: none;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--text-secondary);
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  padding: 0.3rem 0.75rem;
  border-radius: var(--radius-sm);
  transition: all 0.2s ease;
  white-space: nowrap;
}

.file-link:hover {
  border-color: var(--accent-blue);
  color: var(--text-primary);
  background: var(--bg-surface-elevated);
}

.file-link.active {
  background: rgba(56, 189, 248, 0.15);
  border-color: var(--accent-blue);
  color: var(--accent-blue);
  font-weight: 600;
}

.nav-home-link {
  font-weight: 700;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  color: var(--accent-blue);
  background: rgba(56, 189, 248, 0.08);
  border-color: rgba(56, 189, 248, 0.35);
}

.nav-home-link:hover {
  background: rgba(56, 189, 248, 0.2);
  color: #fff;
  border-color: var(--accent-blue);
}

.file-nav-divider {
  color: rgba(148, 163, 184, 0.35);
  font-size: 0.85rem;
  user-select: none;
  margin: 0 0.15rem;
  display: inline-block;
}

/* Header Actions (Home + Chapter Select + Language Selector) */
.header-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.nav-btn-home {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: var(--bg-surface);
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  font-size: 0.82rem;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.2s ease;
  white-space: nowrap;
}

.nav-btn-home:hover {
  background: var(--bg-surface-elevated);
  border-color: var(--accent-blue);
  color: var(--accent-blue);
  box-shadow: 0 0 0 2px rgba(56, 189, 248, 0.15);
  transform: translateY(-1px);
}

.chapter-switcher {
  display: inline-flex;
  align-items: center;
  background: var(--bg-surface);
  padding: 0.35rem 0.65rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

.chapter-switcher:hover,
.chapter-switcher:focus-within {
  border-color: var(--accent-blue);
  box-shadow: 0 0 0 2px rgba(56, 189, 248, 0.15);
}

.chapter-select {
  background: transparent;
  border: none;
  color: var(--text-primary);
  font-size: 0.82rem;
  font-weight: 600;
  cursor: pointer;
  font-family: var(--font-sans);
  outline: none;
  max-width: 220px;
}

.chapter-select option {
  background: var(--bg-surface);
  color: var(--text-primary);
}

.chapter-select option:disabled {
  color: var(--text-muted);
}

/* Language Selector (Dropdown) */
.lang-switcher {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  background: var(--bg-surface);
  padding: 0.35rem 0.7rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

.lang-switcher:hover,
.lang-switcher:focus-within {
  border-color: var(--accent-blue);
  box-shadow: 0 0 0 2px rgba(56, 189, 248, 0.15);
}

.lang-icon {
  font-size: 0.9rem;
  line-height: 1;
  user-select: none;
}

.lang-select {
  background: transparent;
  border: none;
  color: var(--text-primary);
  font-size: 0.82rem;
  font-weight: 600;
  padding-right: 0.35rem;
  cursor: pointer;
  font-family: var(--font-sans);
  outline: none;
}

.lang-select option {
  background: var(--bg-surface);
  color: var(--text-primary);
}

/* Controls Bar */
.controls-bar {
  max-width: 1440px;
  width: 100%;
  margin: 1rem auto 0;
  padding: 0 1.5rem;
}

.controls-inner {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 0.75rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
  box-shadow: var(--shadow-md);
}

.btn-group {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.ctrl-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: var(--bg-surface-elevated);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
  padding: 0.45rem 0.9rem;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
  font-family: var(--font-sans);
}

.ctrl-btn:hover:not(:disabled) {
  border-color: var(--accent-blue);
  background: rgba(56, 189, 248, 0.12);
  transform: translateY(-1px);
}

.ctrl-btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.ctrl-btn.primary {
  background: linear-gradient(135deg, #0284c7, #2563eb);
  border-color: #38bdf8;
  color: #fff;
}

.ctrl-btn.primary:hover:not(:disabled) {
  background: linear-gradient(135deg, #0369a1, #1d4ed8);
  box-shadow: 0 0 12px rgba(56, 189, 248, 0.4);
}

/* Step Dots / Timeline */
.step-timeline {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  flex: 1;
  justify-content: center;
  flex-wrap: wrap;
}

.step-dot {
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border: 1px solid var(--border-color);
  background: var(--bg-card);
  color: var(--text-muted);
  font-size: 0.78rem;
  font-weight: 700;
  font-family: var(--font-mono);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all 0.2s ease;
}

.step-dot:hover {
  border-color: var(--accent-blue);
  color: var(--text-primary);
}

.step-dot.done {
  background: rgba(52, 211, 153, 0.15);
  border-color: var(--accent-emerald);
  color: var(--accent-emerald);
}

.step-dot.active {
  background: var(--accent-blue);
  border-color: #fff;
  color: #0f172a;
  transform: scale(1.12);
  box-shadow: 0 0 12px rgba(56, 189, 248, 0.6);
}

.speed-control {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.8rem;
  color: var(--text-muted);
}

.speed-select {
  background: var(--bg-card);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
  padding: 0.3rem 0.5rem;
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
  font-family: var(--font-mono);
}

/* Main Workspace Layout */
.sim-workspace {
  max-width: 1440px;
  width: 100%;
  margin: 1rem auto 2rem;
  padding: 0 1.5rem;
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(0, 1.15fr);
  gap: 1.25rem;
  flex: 1;
}

@media (max-width: 1024px) {
  .sim-workspace {
    grid-template-columns: minmax(0, 1fr);
  }
}

/* Panels */
.panel {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  overflow: hidden;
  display: flex;
  flex-direction: column;
  box-shadow: var(--shadow-md);
}

.panel-header {
  background: rgba(15, 23, 42, 0.6);
  padding: 0.7rem 1.1rem;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
}

.panel-title {
  font-size: 0.88rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.4rem;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.panel-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-shrink: 0;
}

.copy-code-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--bg-surface-elevated);
  color: var(--text-secondary);
  border: 1px solid var(--border-color);
  padding: 0.22rem 0.65rem;
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 600;
  font-family: var(--font-sans);
  white-space: nowrap;
  flex-shrink: 0;
  cursor: pointer;
  transition: all 0.18s ease;
}

.copy-code-btn:hover {
  color: var(--text-primary);
  border-color: var(--accent-blue);
  background: rgba(56, 189, 248, 0.12);
}

.copy-code-btn.copied {
  color: var(--accent-emerald);
  border-color: var(--accent-emerald);
  background: rgba(52, 211, 153, 0.15);
}

.panel-badge {
  font-family: var(--font-mono);
  font-size: 0.73rem;
  color: var(--accent-blue);
  white-space: nowrap;
  flex-shrink: 0;
  background: rgba(56, 189, 248, 0.12);
  padding: 0.15rem 0.55rem;
  border-radius: 999px;
  border: 1px solid rgba(56, 189, 248, 0.3);
}

/* Code Panel */
.code-container {
  background: var(--bg-code);
  padding: 0.85rem 0;
  font-family: var(--font-mono);
  font-size: 0.88rem;
  overflow-x: auto;
  flex: 1;
}

.code-line {
  display: flex;
  align-items: center;
  justify-content: flex-start;
  padding: 0.22rem 1rem 0.22rem 0.5rem;
  border-left: 3px solid transparent;
  transition: background-color 0.2s ease, border-color 0.2s ease;
  position: relative;
  min-height: 1.75rem;
  min-width: 100%;
  width: max-content;
}

.code-line.executable {
  cursor: pointer;
}

.code-line.executable:hover {
  background: rgba(255, 255, 255, 0.04);
}

.code-line.executed {
  background: rgba(52, 211, 153, 0.05);
  border-left-color: rgba(52, 211, 153, 0.5);
}

.code-line.active {
  background: rgba(56, 189, 248, 0.16);
  border-left-color: var(--accent-blue);
  box-shadow: inset 0 0 12px rgba(56, 189, 248, 0.08);
}

.line-indicator {
  flex: 0 0 1.5rem;
  width: 1.5rem;
  min-width: 1.5rem;
  text-align: center;
  color: var(--accent-blue);
  font-size: 0.75rem;
  font-weight: 700;
  user-select: none;
}

.line-num {
  flex: 0 0 2.4rem;
  width: 2.4rem;
  min-width: 2.4rem;
  text-align: right;
  padding-right: 0.85rem;
  color: #475569;
  user-select: none;
  font-size: 0.78rem;
}

.line-content {
  white-space: pre;
  color: var(--text-primary);
  flex: 0 0 auto;
}

.line-badge-slot {
  flex: 0 0 auto;
  display: inline-flex;
  align-items: center;
}

.line-eval-badge {
  flex-shrink: 0;
  margin-left: 0.75rem;
  font-size: 0.74rem;
  padding: 0.1rem 0.5rem;
  border-radius: 4px;
  background: rgba(251, 191, 36, 0.15);
  border: 1px solid rgba(251, 191, 36, 0.4);
  color: var(--accent-amber);
  font-family: var(--font-mono);
  animation: fadeInSlide 0.25s ease-out;
  white-space: nowrap;
}

/* Syntax Highlighting Classes */
.syn-comment { color: var(--syntax-comment); font-style: italic; }
.syn-kw { color: var(--syntax-keyword); font-weight: 600; }
.syn-func { color: var(--syntax-func); }
.syn-str { color: var(--syntax-string); }
.syn-num { color: var(--syntax-number); }
.syn-op { color: var(--syntax-op); font-weight: 600; }
.syn-fbrace { color: var(--accent-amber); font-weight: 700; }

/* Right Column Stack */
.right-column {
  display: flex;
  flex-direction: column;
  gap: 1.15rem;
}

/* Memory & Variable State Cards */
.memory-grid {
  padding: 1rem;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(155px, 1fr));
  gap: 0.75rem;
  min-height: 92px;
}

.memory-empty {
  grid-column: 1 / -1;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  font-size: 0.85rem;
  font-style: italic;
  min-height: 68px;
  border: 1px dashed var(--border-color);
  border-radius: var(--radius-md);
}

.var-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 0.65rem 0.85rem;
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  position: relative;
  transition: all 0.25s ease;
}

.var-card.updated {
  border-color: var(--accent-amber);
  background: rgba(251, 191, 36, 0.08);
  box-shadow: 0 0 15px rgba(251, 191, 36, 0.2);
  animation: popScale 0.3s ease;
}

.var-card.read {
  border-color: var(--accent-blue);
  box-shadow: 0 0 12px rgba(56, 189, 248, 0.2);
}

.var-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.var-name {
  font-family: var(--font-mono);
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--accent-blue);
}

.var-type {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  padding: 0.08rem 0.4rem;
  border-radius: 4px;
  background: rgba(129, 140, 248, 0.15);
  color: var(--accent-indigo);
}

.var-value {
  font-family: var(--font-mono);
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-primary);
  word-break: break-all;
}

.var-prev {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--text-muted);
  text-decoration: line-through;
}

/* Visual Stage (Interactive Operation Visualizer) */
.visual-stage {
  padding: 1.1rem;
  background: var(--bg-card);
  border-top: 1px solid var(--border-color);
  min-height: 155px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 0.85rem;
}

.vis-formula-box {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.6rem;
  padding: 0.75rem;
  background: rgba(15, 23, 42, 0.7);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  font-family: var(--font-mono);
}

.vis-chip {
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-sm);
  font-weight: 700;
  font-size: 0.95rem;
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
}

.vis-chip.var {
  color: var(--accent-blue);
  border-color: rgba(56, 189, 248, 0.4);
}

.vis-chip.op {
  color: var(--accent-amber);
  background: rgba(251, 191, 36, 0.12);
  border-color: rgba(251, 191, 36, 0.4);
}

.vis-chip.res {
  color: var(--accent-emerald);
  background: rgba(52, 211, 153, 0.15);
  border-color: rgba(52, 211, 153, 0.5);
  font-size: 1.05rem;
}

.vis-chip.bool-true {
  color: var(--accent-emerald);
  background: rgba(52, 211, 153, 0.18);
  border-color: var(--accent-emerald);
}

.vis-chip.bool-false {
  color: var(--accent-rose);
  background: rgba(251, 113, 133, 0.18);
  border-color: var(--accent-rose);
}

/* Visual Block Grid for Division/Remainder & Alignment */
.vis-blocks-wrap {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  justify-content: center;
  align-items: center;
}

.vis-quotient-group {
  display: inline-flex;
  gap: 0.25rem;
  padding: 0.35rem 0.5rem;
  border: 1.5px solid var(--accent-blue);
  background: rgba(56, 189, 248, 0.1);
  border-radius: var(--radius-sm);
  align-items: center;
}

.vis-remainder-group {
  display: inline-flex;
  gap: 0.25rem;
  padding: 0.35rem 0.5rem;
  border: 1.5px dashed var(--accent-amber);
  background: rgba(251, 191, 36, 0.15);
  border-radius: var(--radius-sm);
  align-items: center;
}

.vis-dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--accent-blue);
}

.vis-dot.rem {
  background: var(--accent-amber);
}

/* Character Cell Alignment Grid (for f-string alignment) */
.char-grid {
  display: inline-flex;
  border: 1px solid var(--border-highlight);
  border-radius: var(--radius-sm);
  overflow: hidden;
  font-family: var(--font-mono);
  margin: 0 auto;
}

.char-cell {
  min-width: 28px;
  height: 34px;
  padding: 0 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-right: 1px solid var(--border-color);
  background: var(--bg-surface);
  font-size: 0.85rem;
  font-weight: 600;
}

.char-cell.space {
  background: rgba(251, 191, 36, 0.1);
  color: var(--accent-amber);
  font-size: 0.7rem;
}

.char-cell.end-bar {
  background: rgba(251, 113, 133, 0.2);
  color: var(--accent-rose);
  border-right: none;
  font-weight: 800;
}

/* Step Explanation Card */
.explanation-body {
  padding: 1.1rem 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.exp-step-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--accent-blue);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.exp-text {
  font-size: 0.92rem;
  color: var(--text-secondary);
  line-height: 1.65;
}

.exp-tip {
  background: rgba(56, 189, 248, 0.08);
  border-left: 3px solid var(--accent-blue);
  padding: 0.65rem 0.9rem;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-size: 0.84rem;
  color: var(--text-primary);
}

.exp-tip strong {
  color: var(--accent-amber);
}

/* Terminal / Console Output */
.terminal-body {
  background: var(--bg-terminal);
  padding: 1rem 1.2rem;
  font-family: var(--font-mono);
  font-size: 0.88rem;
  min-height: 120px;
  color: #e2e8f0;
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
}

.term-line {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  white-space: pre-wrap;
  padding: 0.15rem 0.4rem;
  border-radius: 4px;
}

.term-line.latest {
  background: rgba(52, 211, 153, 0.14);
  color: #6ee7b7;
  border-left: 2px solid var(--accent-emerald);
  animation: fadeInSlide 0.25s ease-out;
}

.term-prompt {
  color: var(--accent-emerald);
  user-select: none;
  font-weight: 700;
}

.term-empty {
  color: #64748b;
  font-style: italic;
  font-size: 0.82rem;
}

/* Footer Shortcut Hints */
.sim-footer {
  max-width: 1440px;
  width: 100%;
  margin: 0 auto 1.5rem;
  padding: 0 1.5rem;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.78rem;
}

.kbd {
  display: inline-block;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 4px;
  padding: 0.05rem 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--text-secondary);
  margin: 0 0.15rem;
}

@keyframes fadeInSlide {
  from {
    opacity: 0;
    transform: translateX(-6px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes popScale {
  0% { transform: scale(0.96); }
  50% { transform: scale(1.03); }
  100% { transform: scale(1); }
}

/* Scenario / Input Preset Bar (for interactive input & branching chapters) */
.scenario-bar {
  background: rgba(15, 23, 42, 0.75);
  border-bottom: 1px solid var(--border-color);
  padding: 0.55rem 1rem;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.scenario-label {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--accent-amber);
  margin-right: 0.2rem;
  white-space: nowrap;
}

.scenario-btn {
  background: var(--bg-surface-elevated);
  color: var(--text-secondary);
  border: 1px solid var(--border-color);
  padding: 0.25rem 0.65rem;
  border-radius: 999px;
  font-size: 0.75rem;
  font-weight: 600;
  font-family: var(--font-sans);
  cursor: pointer;
  transition: all 0.18s ease;
  white-space: nowrap;
}

.scenario-btn:hover {
  color: var(--text-primary);
  border-color: var(--accent-blue);
}

.scenario-btn.active {
  background: rgba(56, 189, 248, 0.18);
  color: var(--accent-blue);
  border-color: var(--accent-blue);
  box-shadow: 0 0 10px rgba(56, 189, 248, 0.25);
}

/* Skipped Code Lines & Boolean Badges */
.code-line.skipped {
  opacity: 0.42;
  background: rgba(15, 23, 42, 0.35);
}

.code-line.skipped .line-indicator {
  color: var(--text-muted);
}

.line-eval-badge.bool-true {
  background: rgba(52, 211, 153, 0.16);
  border-color: rgba(52, 211, 153, 0.55);
  color: var(--accent-emerald);
}

.line-eval-badge.bool-false {
  background: rgba(251, 113, 133, 0.16);
  border-color: rgba(251, 113, 133, 0.55);
  color: var(--accent-rose);
}

/* Conditional Branch Visualizer Cards */
.branch-flow {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.55rem;
}

.branch-node {
  padding: 0.4rem 0.8rem;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.82rem;
  font-weight: 600;
  border: 1px solid var(--border-color);
  background: var(--bg-surface);
  color: var(--text-muted);
  transition: all 0.25s ease;
}

.branch-node.active-true {
  border-color: var(--accent-emerald);
  background: rgba(52, 211, 153, 0.16);
  color: var(--accent-emerald);
  box-shadow: 0 0 12px rgba(52, 211, 153, 0.25);
}

.branch-node.active-false {
  border-color: var(--accent-rose);
  background: rgba(251, 113, 133, 0.14);
  color: var(--accent-rose);
}

.branch-node.skipped-node {
  opacity: 0.45;
  text-decoration: line-through;
}

.term-input-val {
  color: var(--accent-amber);
  font-weight: 700;
  background: rgba(251, 191, 36, 0.15);
  padding: 0.05rem 0.35rem;
  border-radius: 3px;
  border: 1px dashed rgba(251, 191, 36, 0.45);
}

/* ===== Sequence (List / Tuple) Visualizer — CH08 ===== */
.var-card.wide {
  grid-column: 1 / -1;
}

.terminal-body.scrollable {
  max-height: 420px;
  overflow-y: auto;
}

.seq-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.3rem;
}

.seq-label {
  font-family: var(--font-mono);
  font-size: 0.76rem;
  color: var(--text-muted);
  text-align: center;
}

.seq-label b {
  color: var(--accent-blue);
}

.seq-row {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.3rem;
}

.seq-bracket {
  font-family: var(--font-mono);
  font-size: 1.6rem;
  font-weight: 300;
  color: var(--text-muted);
  padding: 0 0.1rem;
}

.seq-wrap.tuple .seq-bracket {
  color: var(--accent-purple);
}

.seq-empty {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--text-muted);
  font-style: italic;
}

.seq-cell {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.2rem;
  transition: opacity 0.25s ease;
}

.seq-idx {
  font-family: var(--font-mono);
  font-size: 0.66rem;
  color: #64748b;
  min-height: 0.95rem;
  line-height: 0.95rem;
}

.seq-idx.neg {
  color: rgba(251, 113, 133, 0.7);
}

.seq-box {
  min-width: 44px;
  height: 38px;
  padding: 0 0.55rem;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  background: var(--bg-surface);
  font-family: var(--font-mono);
  font-size: 0.86rem;
  font-weight: 700;
  color: var(--text-primary);
  white-space: nowrap;
  transition: all 0.25s ease;
}

.seq-wrap.tuple .seq-box {
  border-color: rgba(192, 132, 252, 0.5);
  background: rgba(192, 132, 252, 0.08);
}

.seq-cell.hl .seq-box {
  border-color: var(--accent-amber);
  background: rgba(251, 191, 36, 0.14);
  color: var(--accent-amber);
  box-shadow: 0 0 12px rgba(251, 191, 36, 0.25);
}

.seq-cell.hl .seq-idx {
  color: var(--accent-amber);
  font-weight: 800;
}

.seq-cell.sel .seq-box {
  border-color: var(--accent-emerald);
  background: rgba(52, 211, 153, 0.15);
  color: var(--accent-emerald);
}

.seq-cell.sel .seq-idx {
  color: var(--accent-emerald);
  font-weight: 800;
}

.seq-cell.dim {
  opacity: 0.35;
}

.seq-cell.new .seq-box {
  border-color: var(--accent-emerald);
  background: rgba(52, 211, 153, 0.18);
  color: var(--accent-emerald);
  box-shadow: 0 0 12px rgba(52, 211, 153, 0.3);
  animation: popScale 0.35s ease;
}

.seq-cell.changed .seq-box {
  border-color: var(--accent-amber);
  background: rgba(251, 191, 36, 0.18);
  color: var(--accent-amber);
  animation: popScale 0.35s ease;
}

.seq-cell.shift .seq-box {
  border-style: dashed;
  border-color: var(--accent-blue);
}

.seq-cell.removed .seq-box {
  border: 1.5px dashed var(--accent-rose);
  background: rgba(251, 113, 133, 0.1);
  color: var(--accent-rose);
  text-decoration: line-through;
}

.seq-cell.removed .seq-idx {
  color: var(--accent-rose);
}

.seq-cell.stop .seq-box {
  border: 1.5px dashed var(--accent-rose);
  color: var(--text-muted);
}

.seq-cell.stop .seq-idx {
  color: var(--accent-rose);
  font-weight: 800;
}

.seq-cell.locked .seq-box {
  border: 1.5px solid var(--accent-rose);
  background: rgba(251, 113, 133, 0.14);
  color: var(--accent-rose);
}

.seq-arrow {
  text-align: center;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--accent-amber);
}

/* ===== Dict / Set / Venn Visualizer — CH09 ===== */
.seq-wrap.dict .seq-idx {
  font-size: 0.74rem;
  font-weight: 700;
  color: var(--accent-blue);
}

.seq-wrap.dict .seq-bracket,
.seq-wrap.set .seq-bracket {
  color: var(--accent-amber);
}

.seq-wrap.set .seq-box {
  border-radius: 999px;
  border-color: rgba(52, 211, 153, 0.45);
}

.seq-cell.missing .seq-box {
  border: 1.5px dashed var(--text-muted);
  background: transparent;
  color: var(--text-muted);
}

.seq-cell.missing .seq-idx {
  color: var(--accent-rose);
}

.venn-svg {
  display: block;
  width: 100%;
  max-width: 440px;
  margin: 0 auto;
}

.seq-nowrap {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
}