/* CROWNED — Design System with Light Theme (Default) & Dark Theme */

:root {
  /* LIGHT THEME (Default) */
  --bg-primary: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-elevated: #f1f5f9;
  --bg-card: #ffffff;
  --bg-card-hover: #f8fafc;

  --border-subtle: #e2e8f0;
  --border-medium: #cbd5e1;
  --border-strong: #94a3b8;
  --border-focus: #7c3aed;

  --accent-purple-light: #7c3aed;
  --accent-purple: #7c3aed;
  --accent-purple-dark: #6d28d9;
  --accent-purple-subtle: #f5f3ff;
  --accent-glow: rgba(124, 58, 237, 0.15);

  --text-primary: #0f172a;
  --text-secondary: #334155;
  --text-muted: #64748b;
  --text-dim: #94a3b8;

  --color-success: #059669;
  --color-success-bg: #ecfdf5;
  --color-success-border: #a7f3d0;

  --color-danger: #e11d48;
  --color-danger-bg: #fff1f2;
  --color-danger-border: #fecdd3;

  --color-warn: #d97706;
  --color-warn-bg: #fffbeb;
  --color-warn-border: #fde68a;

  --header-bg: rgba(255, 255, 255, 0.88);
  --equation-box-bg: #f8fafc;
  --equation-box-border: #e2e8f0;
  --card-shadow: 0 4px 20px -2px rgba(0, 0, 0, 0.05), 0 2px 6px -1px rgba(0, 0, 0, 0.02);
  --card-shadow-elevated: 0 10px 30px -4px rgba(124, 58, 237, 0.08), 0 4px 6px -2px rgba(0, 0, 0, 0.03);
  --input-bg: #ffffff;
  --input-color: #0f172a;
  --input-focus-bg: #ffffff;
  --key-hint-bg: #f1f5f9;
  --key-hint-border: #cbd5e1;
  --key-hint-color: #475569;
  --glow-bg: radial-gradient(circle, rgba(124, 58, 237, 0.08) 0%, rgba(248, 250, 252, 0) 70%);

  --font-sans: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'Fira Code', 'JetBrains Mono', monospace;

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 9999px;

  --transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

[data-theme="dark"] {
  /* DARK THEME */
  --bg-primary: #0a0612;
  --bg-surface: #120b20;
  --bg-surface-elevated: #1a102e;
  --bg-card: rgba(22, 14, 38, 0.75);
  --bg-card-hover: rgba(30, 20, 52, 0.85);

  --border-subtle: rgba(147, 51, 234, 0.15);
  --border-medium: rgba(147, 51, 234, 0.3);
  --border-strong: rgba(168, 85, 247, 0.55);
  --border-focus: #a855f7;

  --accent-purple-light: #d8b4fe;
  --accent-purple: #a855f7;
  --accent-purple-dark: #7c3aed;
  --accent-purple-subtle: rgba(168, 85, 247, 0.18);
  --accent-glow: rgba(168, 85, 247, 0.25);

  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --text-dim: #64748b;

  --color-success: #10b981;
  --color-success-bg: rgba(16, 185, 129, 0.12);
  --color-success-border: rgba(16, 185, 129, 0.35);

  --color-danger: #f43f5e;
  --color-danger-bg: rgba(244, 63, 94, 0.12);
  --color-danger-border: rgba(244, 63, 94, 0.35);

  --color-warn: #f59e0b;
  --color-warn-bg: rgba(245, 158, 11, 0.12);
  --color-warn-border: rgba(245, 158, 11, 0.35);

  --header-bg: rgba(10, 6, 18, 0.82);
  --equation-box-bg: rgba(10, 6, 18, 0.4);
  --equation-box-border: var(--border-subtle);
  --card-shadow: 0 16px 36px -10px rgba(0, 0, 0, 0.5), 0 0 0 1px rgba(168, 85, 247, 0.08);
  --card-shadow-elevated: 0 20px 40px -10px rgba(124, 58, 237, 0.15);
  --input-bg: var(--bg-surface-elevated);
  --input-color: #ffffff;
  --input-focus-bg: #22123d;
  --key-hint-bg: rgba(0, 0, 0, 0.35);
  --key-hint-border: rgba(255, 255, 255, 0.15);
  --key-hint-color: var(--text-secondary);
  --glow-bg: radial-gradient(circle, rgba(124, 58, 237, 0.15) 0%, rgba(10, 6, 18, 0) 70%);
}

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

body {
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-sans);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  line-height: 1.5;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  transition: background-color 0.25s ease, color 0.25s ease;
}

/* Background ambient glow */
.glow-backdrop {
  position: fixed;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 900px;
  height: 450px;
  background: var(--glow-bg);
  pointer-events: none;
  z-index: 0;
  transition: background 0.3s ease;
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--header-bg);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-subtle);
  transition: background 0.25s ease, border-color 0.25s ease;
}

.header-container {
  max-width: 1040px;
  margin: 0 auto;
  padding: 0.85rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.brand {
  display: flex;
  align-items: baseline;
  gap: 0.5rem;
}

.brand-name {
  font-weight: 700;
  font-size: 1.25rem;
  letter-spacing: -0.03em;
  color: var(--text-primary);
}

.brand-dot {
  color: var(--accent-purple);
}

.brand-tag {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--text-muted);
  letter-spacing: 0.05em;
  text-transform: uppercase;
  border-left: 1px solid var(--border-medium);
  padding-left: 0.5rem;
}

/* Nav Tabs */
.nav-tabs {
  display: flex;
  background: var(--bg-surface);
  padding: 3px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-subtle);
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.03);
}

.nav-tab {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  background: transparent;
  border: none;
  color: var(--text-muted);
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 500;
  padding: 0.4rem 0.9rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition);
}

.nav-tab:hover {
  color: var(--text-primary);
}

.nav-tab.active {
  background: var(--bg-surface-elevated);
  color: var(--accent-purple);
  border: 1px solid var(--border-medium);
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.06);
}

[data-theme="dark"] .nav-tab.active {
  color: var(--accent-purple-light);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.4);
}

.header-stats {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.stat-pill {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  padding: 0.3rem 0.75rem;
  border-radius: var(--radius-full);
  font-size: 0.8rem;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.03);
}

.stat-label {
  color: var(--text-dim);
  text-transform: uppercase;
  font-size: 0.7rem;
  letter-spacing: 0.04em;
}

.stat-value {
  font-family: var(--font-mono);
  font-weight: 600;
  color: var(--accent-purple);
}

[data-theme="dark"] .stat-value {
  color: var(--accent-purple-light);
}

.streak-icon {
  font-size: 0.85rem;
}

.icon-btn {
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  width: 34px;
  height: 34px;
  border-radius: var(--radius-sm);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: var(--transition);
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.03);
}

.icon-btn:hover {
  color: var(--text-primary);
  border-color: var(--border-medium);
  background: var(--bg-surface-elevated);
}

/* Main Layout */
.main-content {
  flex: 1;
  max-width: 1040px;
  width: 100%;
  margin: 0 auto;
  padding: 2rem 1.5rem;
  position: relative;
  z-index: 1;
}

.tab-pane {
  display: none;
  animation: fadeIn 0.25s cubic-bezier(0.16, 1, 0.3, 1);
}

.tab-pane.active {
  display: block;
}

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

/* =======================================================
   STAGE-BASED PROGRESSION SYSTEM
   ======================================================= */

.stages-nav-wrapper {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

/* Stage Selector Pills */
.stages-pills-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.stage-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 500;
  padding: 0.5rem 0.9rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition);
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.03);
}

.stage-pill:hover:not(.locked) {
  border-color: var(--accent-purple);
  color: var(--text-primary);
  transform: translateY(-1px);
}

.stage-pill.active {
  background: var(--accent-purple-subtle);
  border-color: var(--accent-purple);
  color: var(--accent-purple-dark);
  font-weight: 600;
  box-shadow: 0 2px 8px rgba(124, 58, 237, 0.15);
}

[data-theme="dark"] .stage-pill.active {
  background: rgba(147, 51, 234, 0.2);
  color: #fff;
  border-color: var(--accent-purple);
}

.stage-pill.locked {
  opacity: 0.5;
  cursor: not-allowed;
  background: var(--bg-surface-elevated);
}

.stage-pill.completed {
  border-color: var(--color-success-border);
}

.stage-pill-icon {
  font-size: 1.05rem;
}

.stage-pill-title {
  font-size: 0.85rem;
}

.stage-pill-count {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  background: var(--bg-surface-elevated);
  padding: 0.15rem 0.4rem;
  border-radius: var(--radius-full);
  color: var(--text-dim);
}

.stage-pill.active .stage-pill-count {
  background: var(--accent-purple);
  color: #fff;
}

/* Stage Info & Level Stepper Card */
.stage-info-card {
  background: var(--bg-card);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-lg);
  padding: 1.5rem 1.75rem;
  box-shadow: var(--card-shadow);
  transition: background 0.25s ease, border-color 0.25s ease;
}

.stage-meta-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 1.25rem;
}

.stage-title-wrap {
  display: flex;
  align-items: center;
  gap: 0.9rem;
}

.stage-badge-icon {
  font-size: 2.2rem;
  line-height: 1;
}

.stage-title-heading {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 0.2rem;
}

.stage-title-heading h2 {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

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

.stage-stat-summary {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.stat-chip {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-subtle);
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-md);
  font-size: 0.82rem;
}

.chip-title {
  color: var(--text-dim);
}

.chip-val {
  font-family: var(--font-mono);
  font-weight: 600;
  color: var(--text-primary);
}

/* Level Stepper Buttons */
.level-stepper-container {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border-subtle);
  overflow-x: auto;
}

.level-stepper-label {
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-dim);
  white-space: nowrap;
}

.level-stepper-buttons {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.4rem;
}

.level-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 36px;
  height: 36px;
  padding: 0 0.5rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
  background: var(--bg-surface);
  color: var(--text-secondary);
  font-family: var(--font-mono);
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
}

.level-btn:hover:not(.locked) {
  border-color: var(--accent-purple);
  color: var(--accent-purple-dark);
  transform: translateY(-1px);
}

.level-btn.current {
  background: var(--accent-purple);
  border-color: var(--accent-purple);
  color: #fff;
  box-shadow: 0 4px 12px rgba(124, 58, 237, 0.35);
  transform: scale(1.06);
}

.level-btn.completed:not(.current) {
  background: var(--color-success-bg);
  border-color: var(--color-success-border);
  color: var(--color-success);
}

.level-btn.locked {
  background: var(--bg-surface-elevated);
  color: var(--text-dim);
  opacity: 0.45;
  cursor: not-allowed;
  font-size: 0.75rem;
}

/* Stage Progress Bar */
.stage-progress-track {
  height: 6px;
  background: var(--bg-surface-elevated);
  border-radius: var(--radius-full);
  margin-top: 1.25rem;
  overflow: hidden;
  border: 1px solid var(--border-subtle);
}

.stage-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent-purple) 0%, #10b981 100%);
  border-radius: var(--radius-full);
  transition: width 0.4s cubic-bezier(0.16, 1, 0.3, 1);
}

/* =======================================================
   EQUATION MAIN CARD
   ======================================================= */

.equation-card {
  background: var(--bg-card);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-lg);
  padding: 2.2rem 2.5rem;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  box-shadow: var(--card-shadow);
  margin-bottom: 2rem;
  position: relative;
  overflow: hidden;
  transition: background 0.25s ease, border-color 0.25s ease, box-shadow 0.25s ease;
}

.card-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 2rem;
}

.meta-tags {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.badge {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius-full);
  background: var(--accent-purple-subtle);
  border: 1px solid var(--border-medium);
  color: var(--accent-purple);
  letter-spacing: 0.02em;
}

[data-theme="dark"] .badge {
  color: var(--accent-purple-light);
}

.badge-accent {
  background: linear-gradient(135deg, var(--accent-purple) 0%, var(--accent-purple-dark) 100%);
  color: #fff !important;
  border-color: transparent;
}

.badge-subtle {
  background: var(--bg-surface);
  border-color: var(--border-subtle);
  color: var(--text-muted);
  font-weight: 500;
}

.task-timer {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--text-dim);
}

/* Interactive Equation Layout */
.equation-container {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 0.75rem 0.5rem;
  padding: 2.25rem 0.75rem;
  background: var(--equation-box-bg);
  border-radius: var(--radius-md);
  border: 1px dashed var(--equation-box-border);
  min-height: 130px;
  margin-bottom: 1.5rem;
  transition: background 0.25s ease, border-color 0.25s ease;
}

.eq-item {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}

.coeff-input {
  width: 50px;
  height: 50px;
  background: var(--input-bg);
  border: 2px solid var(--border-medium);
  border-radius: var(--radius-md);
  color: var(--input-color);
  font-family: var(--font-mono);
  font-size: 1.4rem;
  font-weight: 600;
  text-align: center;
  outline: none;
  transition: var(--transition);
  box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.05);
}

.coeff-input:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px var(--accent-glow), inset 0 1px 3px rgba(0, 0, 0, 0.05);
  background: var(--input-focus-bg);
}

.coeff-input.correct {
  border-color: var(--color-success);
  background: var(--color-success-bg);
  color: var(--color-success);
}

.coeff-input.incorrect {
  border-color: var(--color-danger);
  background: var(--color-danger-bg);
  color: var(--color-danger);
}

.formula-label {
  font-family: var(--font-sans);
  font-size: 1.65rem;
  font-weight: 600;
  color: var(--text-primary);
  letter-spacing: -0.01em;
  user-select: none;
}

.formula-label sub {
  font-size: 1rem;
  font-weight: 500;
  color: var(--accent-purple);
}

[data-theme="dark"] .formula-label sub {
  color: var(--accent-purple-light);
}

.op-symbol {
  font-size: 1.5rem;
  color: var(--text-dim);
  padding: 0 0.3rem;
  user-select: none;
}

.op-arrow {
  color: var(--accent-purple);
  font-size: 1.6rem;
  padding: 0 0.5rem;
  user-select: none;
}

/* Feedback Banner */
.feedback-banner {
  display: none;
  padding: 0.9rem 1.25rem;
  border-radius: var(--radius-md);
  font-size: 0.92rem;
  margin-bottom: 1.5rem;
  animation: fadeIn 0.2s ease-out;
  font-weight: 500;
  line-height: 1.5;
}

.feedback-banner.success {
  display: block;
  background: var(--color-success-bg);
  border: 1px solid var(--color-success-border);
  color: var(--color-success);
}

.feedback-banner.stage-cleared {
  display: block;
  background: linear-gradient(135deg, var(--color-success-bg) 0%, var(--accent-purple-subtle) 100%);
  border: 2px solid var(--color-success);
  color: var(--text-primary);
  box-shadow: 0 4px 16px rgba(16, 185, 129, 0.15);
}

.feedback-banner.error {
  display: block;
  background: var(--color-danger-bg);
  border: 1px solid var(--color-danger-border);
  color: var(--color-danger);
}

.feedback-banner.info {
  display: block;
  background: var(--accent-purple-subtle);
  border: 1px solid var(--border-medium);
  color: var(--accent-purple);
}

[data-theme="dark"] .feedback-banner.success {
  color: #6ee7b7;
}

[data-theme="dark"] .feedback-banner.error {
  color: #fda4af;
}

[data-theme="dark"] .feedback-banner.info {
  color: var(--accent-purple-light);
}

/* Action Buttons */
.action-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.action-left, .action-right {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-family: var(--font-sans);
  font-size: 0.9rem;
  font-weight: 600;
  padding: 0.65rem 1.2rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition);
  border: 1px solid transparent;
  user-select: none;
}

.btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.btn-primary {
  background: linear-gradient(135deg, var(--accent-purple) 0%, var(--accent-purple-dark) 100%);
  color: #fff;
  box-shadow: 0 4px 14px rgba(124, 58, 237, 0.25);
}

.btn-primary:hover:not(:disabled) {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px rgba(124, 58, 237, 0.4);
}

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

.btn-secondary:hover:not(:disabled) {
  background: var(--border-subtle);
  border-color: var(--border-strong);
}

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

.btn-outline:hover:not(:disabled) {
  border-color: var(--border-medium);
  color: var(--text-primary);
  background: var(--bg-surface);
}

.key-hint {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  font-weight: 500;
  background: var(--key-hint-bg);
  border: 1px solid var(--key-hint-border);
  padding: 0.1rem 0.35rem;
  border-radius: var(--radius-sm);
  margin-left: 0.3rem;
  color: var(--key-hint-color);
}

.card-footer-tip {
  margin-top: 1.5rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border-subtle);
  font-size: 0.78rem;
  color: var(--text-dim);
  text-align: center;
}

.card-footer-tip code {
  font-family: var(--font-mono);
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-subtle);
  padding: 0.1rem 0.3rem;
  border-radius: var(--radius-sm);
  color: var(--accent-purple);
}

[data-theme="dark"] .card-footer-tip code {
  color: var(--accent-purple-light);
}

/* History Section */
.history-section {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  box-shadow: var(--card-shadow);
  transition: background 0.25s ease, border-color 0.25s ease;
}

.section-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1rem;
}

.section-heading h3 {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.history-controls {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.history-count {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-dim);
}

.btn-ghost-sm {
  background: transparent;
  border: none;
  color: var(--text-dim);
  font-size: 0.75rem;
  cursor: pointer;
  padding: 0.2rem 0.4rem;
  text-decoration: underline;
  text-underline-offset: 2px;
  transition: var(--transition);
}

.btn-ghost-sm:hover {
  color: var(--text-secondary);
}

.history-list {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.history-empty {
  font-size: 0.85rem;
  color: var(--text-dim);
  text-align: center;
  padding: 1.5rem 0;
}

.history-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  padding: 0.65rem 1rem;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  gap: 0.75rem;
}

.history-main {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.history-eq {
  font-family: var(--font-sans);
  font-weight: 500;
  color: var(--text-primary);
}

.history-eq sub {
  color: var(--accent-purple);
}

[data-theme="dark"] .history-eq sub {
  color: var(--accent-purple-light);
}

.history-meta {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-size: 0.75rem;
  color: var(--text-dim);
  white-space: nowrap;
}

/* =======================================================
   SOLVER MODE VIEW
   ======================================================= */

.solver-header {
  margin-bottom: 1.75rem;
}

.solver-header h2 {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: 0.4rem;
  color: var(--text-primary);
}

.solver-desc {
  font-size: 0.9rem;
  color: var(--text-muted);
}

.solver-input-card {
  background: var(--bg-card);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: var(--card-shadow);
  margin-bottom: 1.5rem;
  transition: background 0.25s ease, border-color 0.25s ease;
}

.input-wrapper {
  display: flex;
  gap: 0.75rem;
  margin-bottom: 1.25rem;
}

.solver-input {
  flex: 1;
  background: var(--input-bg);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-md);
  padding: 0.85rem 1.2rem;
  color: var(--input-color);
  font-family: var(--font-mono);
  font-size: 1.05rem;
  outline: none;
  transition: var(--transition);
}

.solver-input:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.presets-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
}

.presets-label {
  font-size: 0.8rem;
  color: var(--text-dim);
  font-weight: 500;
}

.preset-pill {
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  font-family: var(--font-sans);
  font-size: 0.78rem;
  padding: 0.3rem 0.65rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition);
}

.preset-pill:hover {
  background: var(--bg-surface-elevated);
  color: var(--accent-purple);
  border-color: var(--border-medium);
}

[data-theme="dark"] .preset-pill:hover {
  color: var(--accent-purple-light);
}

/* Solver Result Card */
.solver-result-card {
  background: var(--bg-card);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--card-shadow-elevated);
  margin-bottom: 1.5rem;
  animation: fadeIn 0.25s ease-out;
  transition: background 0.25s ease, border-color 0.25s ease;
}

.result-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.5rem;
}

.result-badge {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.25rem 0.65rem;
  border-radius: var(--radius-full);
  background: var(--color-success-bg);
  border: 1px solid var(--color-success-border);
  color: var(--color-success);
}

[data-theme="dark"] .result-badge {
  color: #34d399;
}

.balanced-formula-display {
  font-size: 1.85rem;
  font-weight: 700;
  text-align: center;
  padding: 1.75rem 1rem;
  background: var(--equation-box-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-medium);
  margin-bottom: 2rem;
  letter-spacing: -0.01em;
  color: var(--text-primary);
}

.balanced-formula-display .coeff-highlight {
  color: var(--accent-purple);
  font-family: var(--font-mono);
  font-weight: 700;
  margin-right: 0.15rem;
}

[data-theme="dark"] .balanced-formula-display .coeff-highlight {
  color: #c084fc;
}

.balanced-formula-display sub {
  font-size: 1.1rem;
  color: var(--accent-purple);
}

[data-theme="dark"] .balanced-formula-display sub {
  color: var(--accent-purple-light);
}

.balanced-formula-display .arrow {
  color: var(--accent-purple);
  padding: 0 0.6rem;
}

.result-breakdown h4 {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 0.75rem;
}

.atom-table-wrapper {
  overflow-x: auto;
}

.atom-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.88rem;
  text-align: left;
}

.atom-table th, .atom-table td {
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--border-subtle);
}

.atom-table th {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-dim);
  font-weight: 600;
}

.atom-table td {
  font-family: var(--font-mono);
  color: var(--text-secondary);
}

.status-ok {
  color: var(--color-success);
  font-weight: 600;
}

/* Solver Error Card */
.solver-error-card {
  display: flex;
  align-items: flex-start;
  gap: 1rem;
  background: var(--color-danger-bg);
  border: 1px solid var(--color-danger-border);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  margin-bottom: 1.5rem;
}

.error-icon {
  font-size: 1.5rem;
}

.error-content h4 {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--color-danger);
  margin-bottom: 0.2rem;
}

.error-content p {
  font-size: 0.85rem;
  color: var(--text-secondary);
}

/* =======================================================
   THEORY GRID
   ======================================================= */

.theory-layout {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.25rem;
}

.theory-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  position: relative;
  display: flex;
  flex-direction: column;
  box-shadow: var(--card-shadow);
  transition: background 0.25s ease, border-color 0.25s ease;
}

.theory-badge {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--accent-purple);
  margin-bottom: 0.5rem;
}

.theory-card h3 {
  font-size: 1.15rem;
  font-weight: 600;
  margin-bottom: 0.75rem;
  color: var(--text-primary);
}

.theory-card p {
  font-size: 0.88rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin-bottom: 1rem;
}

.theory-code {
  margin-top: auto;
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  padding: 0.6rem 0.85rem;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  color: var(--accent-purple);
}

[data-theme="dark"] .theory-code {
  color: var(--accent-purple-light);
}

.theory-steps {
  margin-left: 1.25rem;
  font-size: 0.85rem;
  color: var(--text-muted);
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
}

.theory-steps strong {
  color: var(--text-primary);
}

.theory-list {
  margin-left: 1.25rem;
  font-size: 0.85rem;
  color: var(--text-muted);
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
}

.theory-list code {
  font-family: var(--font-mono);
  background: var(--bg-surface-elevated);
  padding: 0.1rem 0.35rem;
  border-radius: 4px;
  color: var(--accent-purple);
}

[data-theme="dark"] .theory-list code {
  color: var(--accent-purple-light);
}

.theory-formula-preview {
  margin-top: auto;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  color: var(--accent-purple);
  background: var(--bg-surface-elevated);
  padding: 0.6rem 0.85rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
  overflow-x: auto;
  white-space: nowrap;
}

[data-theme="dark"] .theory-formula-preview {
  color: var(--accent-purple-light);
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--border-subtle);
  background: var(--bg-surface);
  padding: 1.25rem 1.5rem;
  margin-top: auto;
  z-index: 10;
  transition: background 0.25s ease, border-color 0.25s ease;
}

.footer-container {
  max-width: 1040px;
  margin: 0 auto;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  font-size: 0.8rem;
  color: var(--text-dim);
}

.footer-left {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.footer-brand {
  font-weight: 600;
  color: var(--text-secondary);
}

.badge-keyboard {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-muted);
}

/* =======================================================
   DAILY TASKS
   ======================================================= */

.daily-card {
  background: linear-gradient(135deg, var(--accent-purple-subtle) 0%, var(--bg-card) 60%);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.5rem;
  box-shadow: var(--card-shadow);
  margin-bottom: 1.5rem;
}

.daily-top-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 1rem;
}

.daily-title-wrap {
  display: flex;
  align-items: center;
  gap: 0.9rem;
}

.daily-icon {
  font-size: 2rem;
  line-height: 1;
}

.daily-title-heading {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 0.2rem;
}

.daily-title-heading h2 {
  font-size: 1.15rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.daily-subtitle {
  font-size: 0.82rem;
  color: var(--text-muted);
}

.daily-subtitle b {
  font-family: var(--font-mono);
  color: var(--text-primary);
}

.daily-progress-chip {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-md);
  font-size: 0.82rem;
}

.daily-dots {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

.daily-dot {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  font-family: var(--font-sans);
  font-size: 0.82rem;
  font-weight: 500;
  padding: 0.45rem 0.8rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition);
}

.daily-dot:hover {
  border-color: var(--accent-purple);
  transform: translateY(-1px);
}

.daily-dot.current {
  background: var(--accent-purple);
  border-color: var(--accent-purple);
  color: #fff;
  font-weight: 600;
  box-shadow: 0 4px 12px rgba(124, 58, 237, 0.35);
}

.daily-dot.done {
  border-color: var(--color-success-border);
  background: var(--color-success-bg);
  color: var(--color-success);
}

.daily-progress-track {
  height: 6px;
  background: var(--bg-surface-elevated);
  border-radius: var(--radius-full);
  overflow: hidden;
  border: 1px solid var(--border-subtle);
}

.daily-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent-purple) 0%, #10b981 100%);
  border-radius: var(--radius-full);
  transition: width 0.4s cubic-bezier(0.16, 1, 0.3, 1);
}

/* Material Symbols (icon font) */
.mat {
  font-family: 'Material Symbols Rounded', sans-serif;
  font-weight: normal;
  font-style: normal;
  line-height: 1;
  letter-spacing: normal;
  text-transform: none;
  display: inline-block;
  white-space: nowrap;
  direction: ltr;
  -webkit-font-smoothing: antialiased;
  font-feature-settings: 'liga';
  font-variation-settings: 'FILL' 0, 'wght' 400, 'GRAD' 0, 'opsz' 24;
  vertical-align: -0.15em;
  font-size: 1.1em;
  user-select: none;
}

.stage-badge-icon .mat {
  font-size: 1em;
}

.daily-icon.mat {
  font-size: 2rem;
  vertical-align: baseline;
}

.streak-icon.mat {
  font-size: 1rem;
  color: #f59e0b;
  vertical-align: baseline;
}

.feedback-banner .mat {
  font-size: 1.25em;
  margin-right: 0.15rem;
}

.daily-dot .mat,
.level-btn .mat,
.stage-pill-count .mat {
  font-size: 1.1em;
  vertical-align: -0.2em;
}

.history-time .mat {
  font-size: 1.1em;
}

/* Utility */
.hidden {
  display: none !important;
}

/* Responsive adjustments */
@media (max-width: 768px) {
  .header-container {
    flex-wrap: wrap;
  }
  .nav-tabs {
    order: 3;
    width: 100%;
    justify-content: space-around;
  }
  .stage-meta-row {
    flex-direction: column;
    align-items: flex-start;
  }
  .equation-card {
    padding: 1.5rem 1.25rem;
  }
  .equation-container {
    gap: 0.4rem 0.25rem;
    padding: 1.25rem 0.5rem;
  }
  .coeff-input {
    width: 42px;
    height: 42px;
    font-size: 1.2rem;
  }
  .formula-label {
    font-size: 1.3rem;
  }
  .action-bar {
    flex-direction: column;
    align-items: stretch;
  }
  .action-left, .action-right {
    width: 100%;
    justify-content: space-between;
  }
  .action-left .btn, .action-right .btn {
    flex: 1;
    justify-content: center;
  }
  .input-wrapper {
    flex-direction: column;
  }
}