/* ============================================================
   XL CHEMISTRY PRACTICE: DESIGN SYSTEM
   High-density, distraction-free quantitative workstation theme.
   Strict Zero Em-Dashes Invariant observed.
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Hanken+Grotesk:wght@400;500;600;700;800;900&family=IBM+Plex+Mono:wght@400;500;600&display=swap');

:root {
  /* Surface & Base */
  --xl-bg: #0d131a;
  --xl-surface: #141c24;
  --xl-card: #1b2530;
  --xl-card-hover: #222f3e;
  --xl-border: #2c3b4c;
  --xl-border-soft: #1f2b38;

  /* Typography Colors */
  --xl-ink: #f0f4f8;
  --xl-ink-soft: #cbd5e1;
  --xl-ink-mute: #8192a6;

  /* Brand / Semantic Accents */
  --xl-primary: #38bdf8;       /* Electric cyan */
  --xl-primary-soft: rgba(56, 189, 248, 0.15);
  --xl-indigo: #818cf8;        /* Quantum violet/indigo */
  --xl-indigo-soft: rgba(129, 140, 248, 0.15);
  --xl-good: #34d399;          /* Emerald success */
  --xl-good-soft: rgba(52, 211, 153, 0.15);
  --xl-warn: #fbbf24;          /* Amber alert */
  --xl-warn-soft: rgba(251, 191, 36, 0.15);
  --xl-error: #f87171;         /* Coral error */
  --xl-error-soft: rgba(248, 113, 113, 0.15);

  /* Fonts */
  --font-display: 'Hanken Grotesk', system-ui, -apple-system, sans-serif;
  --font-mono: 'IBM Plex Mono', ui-monospace, SFMono-Regular, monospace;

  /* Standard Typography Tokens */
  --text-2xs: 0.6875rem; /* 11px */
  --text-xs: 0.75rem;    /* 12px */
  --text-sm: 0.875rem;   /* 14px */
  --text-base: 1rem;     /* 16px */
  --text-md: 1.125rem;   /* 18px */
  --text-lg: 1.25rem;    /* 20px */
  --text-xl: 1.5rem;     /* 24px */
  --text-2xl: 1.875rem;  /* 30px */

  /* Layout Rhythm */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
}

/* Light Theme Override */
@media (prefers-color-scheme: light) {
  :root.theme-auto {
    --xl-bg: #f4f7fa;
    --xl-surface: #ffffff;
    --xl-card: #ffffff;
    --xl-card-hover: #f8fafc;
    --xl-border: #d2dbe5;
    --xl-border-soft: #e2e8f0;

    --xl-ink: #0f172a;
    --xl-ink-soft: #334155;
    --xl-ink-mute: #64748b;

    --xl-primary: #0284c7;
    --xl-primary-soft: rgba(2, 132, 199, 0.1);
    --xl-indigo: #4f46e5;
    --xl-indigo-soft: rgba(79, 70, 229, 0.1);
    --xl-good: #059669;
    --xl-good-soft: rgba(5, 150, 105, 0.1);
    --xl-warn: #d97706;
    --xl-warn-soft: rgba(217, 119, 6, 0.1);
    --xl-error: #dc2626;
    --xl-error-soft: rgba(220, 38, 38, 0.1);
  }
}

:root.theme-light,
body.theme-light {
  --xl-bg: #f4f7fa;
  --xl-surface: #ffffff;
  --xl-card: #ffffff;
  --xl-card-hover: #f8fafc;
  --xl-border: #d2dbe5;
  --xl-border-soft: #e2e8f0;

  --xl-ink: #0f172a;
  --xl-ink-soft: #334155;
  --xl-ink-mute: #64748b;

  --xl-primary: #0284c7;
  --xl-primary-soft: rgba(2, 132, 199, 0.1);
  --xl-indigo: #4f46e5;
  --xl-indigo-soft: rgba(79, 70, 229, 0.1);
  --xl-good: #059669;
  --xl-good-soft: rgba(5, 150, 105, 0.1);
  --xl-warn: #d97706;
  --xl-warn-soft: rgba(217, 119, 6, 0.1);
  --xl-error: #dc2626;
  --xl-error-soft: rgba(220, 38, 38, 0.1);
}

:root.theme-dark,
body.theme-dark {
  --xl-bg: #0b0f14;
  --xl-surface: #101720;
  --xl-card: #151e29;
  --xl-card-hover: #1a2533;
  --xl-border: #223041;
  --xl-border-soft: #192330;

  --xl-ink: #f1f5f9;
  --xl-ink-soft: #cbd5e1;
  --xl-ink-mute: #8194a8;

  --xl-primary: #38bdf8;
  --xl-primary-soft: rgba(56, 189, 248, 0.12);
  --xl-indigo: #818cf8;
  --xl-indigo-soft: rgba(129, 140, 248, 0.12);
  --xl-good: #34d399;
  --xl-good-soft: rgba(52, 211, 153, 0.12);
  --xl-warn: #fbbf24;
  --xl-warn-soft: rgba(251, 191, 36, 0.12);
  --xl-error: #f87171;
  --xl-error-soft: rgba(248, 113, 113, 0.12);
}

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

body {
  background-color: var(--xl-bg);
  color: var(--xl-ink);
  font-family: var(--font-display);
  font-size: var(--text-base);
  line-height: 1.5;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Base list styling per user rules */
ul, ol {
  list-style-position: inside;
  padding-left: 1.25rem;
}

/* ============================================================
   STATION HEADER & TOP BAR
   ============================================================ */
.station-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background-color: var(--xl-surface);
  border-bottom: 1px solid var(--xl-border);
  padding: 0.75rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
}

.station-branding {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.station-badge {
  background: linear-gradient(135deg, var(--xl-indigo), var(--xl-primary));
  color: #ffffff;
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: var(--text-xs);
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius-sm);
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.station-title {
  font-weight: 700;
  font-size: var(--text-md);
  color: var(--xl-ink);
}

.station-subtitle {
  font-size: var(--text-xs);
  color: var(--xl-ink-mute);
  font-family: var(--font-mono);
}

.station-center {
  display: flex;
  align-items: center;
  gap: 1.25rem;
  flex: 1;
  max-width: 32rem;
  justify-content: center;
}

.progress-track {
  width: 100%;
  height: 8px;
  background-color: var(--xl-border-soft);
  border-radius: 9999px;
  overflow: hidden;
  position: relative;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--xl-indigo), var(--xl-primary));
  width: 0%;
  transition: width 0.3s ease;
}

.station-metrics {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--xl-ink-soft);
  white-space: nowrap;
}

.station-right {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.student-pill {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  padding: 0.35rem 0.75rem;
  border-radius: 9999px;
  font-size: var(--text-xs);
  color: var(--xl-ink-soft);
  cursor: pointer;
  transition: border-color 0.2s;
}

.student-pill:hover {
  border-color: var(--xl-primary);
}

.student-pill-avatar {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--xl-indigo);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  font-weight: 700;
  font-size: var(--text-2xs);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.5rem 1rem;
  border-radius: var(--radius-sm);
  font-family: var(--font-display);
  font-size: var(--text-sm);
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
  border: 1px solid transparent;
}

.btn-primary {
  background-color: var(--xl-primary);
  color: #0f172a;
}

.btn-primary:hover:not(:disabled) {
  filter: brightness(1.1);
  transform: translateY(-1px);
}

.btn-primary:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none;
}

.btn-secondary {
  background-color: var(--xl-card);
  border-color: var(--xl-border);
  color: var(--xl-ink);
}

.btn-secondary:hover:not(:disabled) {
  border-color: var(--xl-ink-soft);
  background-color: var(--xl-card-hover);
}

.btn-sm {
  padding: 0.3rem 0.65rem;
  font-size: var(--text-xs);
}

/* ============================================================
   MAIN CONTAINER & CARD DECK
   ============================================================ */
.station-body {
  flex: 1;
  max-width: 56rem;
  width: 100%;
  margin: 0 auto;
  padding: 2rem 1.5rem 4rem 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

/* Banner / Overview */
.unit-banner {
  background: linear-gradient(135deg, var(--xl-surface), var(--xl-card));
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
}

.unit-banner-info h1 {
  font-size: var(--text-xl);
  font-weight: 800;
  color: var(--xl-ink);
  margin-bottom: 0.25rem;
}

.unit-banner-info p {
  color: var(--xl-ink-mute);
  font-size: var(--text-sm);
}

.seed-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  padding: 0.25rem 0.5rem;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--xl-primary);
}

/* Problem Card */
.problem-card {
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  transition: border-color 0.2s, box-shadow 0.2s;
  position: relative;
}

.problem-card.status-solved {
  border-color: var(--xl-good);
}

.problem-card.status-exhausted {
  border-color: var(--xl-warn);
}

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
  border-bottom: 1px solid var(--xl-border-soft);
  padding-bottom: 0.75rem;
}

.card-title-group {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.problem-number {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  color: var(--xl-primary);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: 700;
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
}

.problem-topic {
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--xl-ink-mute);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.card-meta-group {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

/* Attempt Pills */
.attempt-track {
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

.attempt-dot {
  width: 9px;
  height: 9px;
  border-radius: 50%;
  background-color: var(--xl-border);
  transition: all 0.2s;
}

.attempt-dot.dot-used {
  background-color: var(--xl-error);
}

.attempt-dot.dot-success {
  background-color: var(--xl-good);
}

.attempt-label {
  font-family: var(--font-mono);
  font-size: var(--text-2xs);
  color: var(--xl-ink-mute);
  margin-left: 0.25rem;
}

/* Problem Prompt */
.problem-stem {
  font-size: var(--text-base);
  color: var(--xl-ink);
  line-height: 1.6;
}

.given-highlight {
  font-family: var(--font-mono);
  color: var(--xl-primary);
  background-color: var(--xl-primary-soft);
  padding: 0.1rem 0.35rem;
  border-radius: var(--radius-sm);
  font-weight: 600;
}

/* ============================================================
   INPUT SYSTEM & SMART PARSER WIDGETS
   ============================================================ */
.input-zone {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-md);
  padding: 1.25rem;
}

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

.input-label {
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--xl-ink-soft);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.input-mode-toggle {
  background: none;
  border: none;
  color: var(--xl-indigo);
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  cursor: pointer;
  text-decoration: underline;
}

.input-mode-toggle:hover {
  filter: brightness(1.2);
}

/* Smart Text Field */
.smart-input-row {
  display: flex;
  align-items: stretch;
  gap: 0.75rem;
}

.smart-input-box {
  flex: 1;
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  color: var(--xl-ink);
  font-family: var(--font-mono);
  font-size: var(--text-md);
  padding: 0.65rem 0.9rem;
  outline: none;
  transition: border-color 0.2s, box-shadow 0.2s;
}

.smart-input-box:focus {
  border-color: var(--xl-primary);
  box-shadow: 0 0 0 2px var(--xl-primary-soft);
}

.smart-input-box:disabled {
  background-color: var(--xl-border-soft);
  color: var(--xl-ink-mute);
  cursor: not-allowed;
}

/* Live Interpretation Preview */
.live-preview-box {
  min-height: 2rem;
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius-sm);
  background-color: var(--xl-card);
  border: 1px dashed var(--xl-border);
  font-size: var(--text-sm);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--xl-ink-soft);
}

.preview-prefix {
  font-family: var(--font-mono);
  font-size: var(--text-2xs);
  color: var(--xl-ink-mute);
  text-transform: uppercase;
}

.preview-content {
  font-family: var(--font-mono);
}

.preview-warning {
  color: var(--xl-warn);
  font-size: var(--text-xs);
}

/* Structured / Split Boxes Fallback */
.split-boxes-row {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 0.75rem;
  align-items: center;
}

.split-col {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}

.split-label {
  font-size: var(--text-2xs);
  color: var(--xl-ink-mute);
  font-family: var(--font-mono);
}

.split-input {
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  color: var(--xl-ink);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  padding: 0.5rem 0.75rem;
  outline: none;
}

.split-input:focus {
  border-color: var(--xl-primary);
}

.split-multiply-symbol {
  font-family: var(--font-mono);
  color: var(--xl-ink-mute);
  font-size: var(--text-md);
  padding-top: 1rem;
}

/* ============================================================
   SPECIALIZED CHEMISTRY WIDGETS
   ============================================================ */

/* 1. Subatomic Table Widget */
.subatomic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(130px, 1fr));
  gap: 0.75rem;
}

.subatomic-cell {
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  padding: 0.75rem;
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.subatomic-cell-label {
  font-size: var(--text-2xs);
  font-family: var(--font-mono);
  color: var(--xl-ink-mute);
  text-transform: uppercase;
}

.subatomic-input {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  color: var(--xl-ink);
  font-family: var(--font-mono);
  font-size: var(--text-md);
  font-weight: 600;
  padding: 0.4rem 0.5rem;
  text-align: center;
  outline: none;
}

.subatomic-input:focus {
  border-color: var(--xl-primary);
}

/* 2. Color Spectrum Picker */
.spectrum-picker {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  margin-top: 0.5rem;
}

.spectrum-pill {
  padding: 0.4rem 0.85rem;
  border-radius: 9999px;
  font-size: var(--text-xs);
  font-weight: 600;
  border: 1px solid var(--xl-border);
  background-color: var(--xl-card);
  color: var(--xl-ink);
  cursor: pointer;
  transition: all 0.2s;
}

.spectrum-pill:hover {
  border-color: var(--xl-primary);
  transform: translateY(-1px);
}

.spectrum-pill.selected {
  border-color: var(--xl-primary);
  background-color: var(--xl-primary);
  color: #0f172a;
}

/* Visible Spectrum Reference Guide (Item 10) */
.spectrum-chart-wrapper {
  margin: 0.6rem 0;
  padding: 0.75rem 0.85rem;
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
}

.spectrum-chart-title {
  font-size: var(--text-2xs);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--xl-ink-mute);
  font-family: var(--font-mono);
  margin-bottom: 0.4rem;
}

.spectrum-gradient-bar {
  height: 14px;
  border-radius: 4px;
  background: linear-gradient(to right, #8b5cf6 0%, #3b82f6 20%, #10b981 45%, #eab308 60%, #f97316 75%, #ef4444 100%);
  border: 1px solid rgba(0, 0, 0, 0.2);
  margin-bottom: 0.5rem;
}

.spectrum-bands-grid {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 0.35rem;
  text-align: center;
}

.spectrum-band-item {
  display: flex;
  flex-direction: column;
  gap: 0.1rem;
  padding: 0.25rem 0.2rem;
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-xs, 4px);
}

.spectrum-band-item .band-name {
  font-size: var(--text-2xs);
  font-weight: 700;
  color: var(--xl-ink);
}

.spectrum-band-item .band-range {
  font-size: 0.65rem;
  font-family: var(--font-mono);
  color: var(--xl-ink-mute);
}

.spectrum-band-item.band-violet { border-top: 3px solid #8b5cf6; }
.spectrum-band-item.band-blue { border-top: 3px solid #3b82f6; }
.spectrum-band-item.band-green { border-top: 3px solid #10b981; }
.spectrum-band-item.band-yellow { border-top: 3px solid #eab308; }
.spectrum-band-item.band-orange { border-top: 3px solid #f97316; }
.spectrum-band-item.band-red { border-top: 3px solid #ef4444; }

@media (max-width: 640px) {
  .spectrum-bands-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

/* 3. Reorderable Ranking Badges */
.ranking-track {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin: 0.75rem 0;
}

.ranking-card {
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  padding: 0.75rem 1rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  cursor: grab;
  user-select: none;
  transition: border-color 0.2s, background-color 0.2s, transform 0.15s, opacity 0.15s;
}

.ranking-card:hover {
  border-color: var(--xl-primary);
  background-color: var(--xl-card-hover);
}

.ranking-card.dragging {
  opacity: 0.4;
  cursor: grabbing;
}

.ranking-card.drag-over {
  border-color: var(--xl-primary);
  box-shadow: 0 0 0 2px var(--xl-primary);
  transform: scale(1.03);
}

/* MCQ Widget Styles */
.mcq-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  margin: 0.5rem 0;
}

.mcq-option {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  padding: 0.65rem 1rem;
  cursor: pointer;
  transition: all 0.15s;
  user-select: none;
}

.mcq-option:hover {
  border-color: var(--xl-primary);
  background-color: var(--xl-card-hover);
}

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

.mcq-indicator {
  width: 16px;
  height: 16px;
  border-radius: 50%;
  border: 2px solid var(--xl-border);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.mcq-option.selected .mcq-indicator {
  border-color: var(--xl-primary);
  background-color: var(--xl-primary);
}

.mcq-indicator::after {
  content: '';
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background-color: #0f172a;
  display: none;
}

.mcq-option.selected .mcq-indicator::after {
  display: block;
}

.mcq-text {
  font-size: var(--text-sm);
  color: var(--xl-ink);
  line-height: 1.4;
}

/* Fill-in multi-field rows */
.fill-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.75rem;
  margin: 0.5rem 0;
}

.fill-label {
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  color: var(--xl-ink-mute);
  text-transform: uppercase;
}

.ranking-symbol {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: var(--text-lg);
  color: var(--xl-primary);
}

.ranking-index {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  width: 24px;
  height: 24px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--xl-ink-mute);
}

/* Fill inputs & Selects */
.fill-input {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  color: var(--xl-ink);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  padding: 0.45rem 0.75rem;
  transition: border-color 0.2s, box-shadow 0.2s;
}

.fill-input:focus {
  outline: none;
  border-color: var(--xl-primary);
  box-shadow: 0 0 0 2px var(--xl-primary-soft);
}

.fill-input:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

.fill-select {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  color: var(--xl-ink);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  padding: 0.45rem 0.75rem;
  transition: border-color 0.2s;
  cursor: pointer;
}

.fill-select:focus {
  outline: none;
  border-color: var(--xl-primary);
}

.fill-select:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

/* Diagram Stage for Particle and Mass Spec SVG */
.diagram-stage {
  width: 100%;
  max-width: 540px;
  margin: 0.5rem 0;
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  padding: 0.75rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
}

.diagram-caption {
  font-family: var(--font-mono);
  font-size: var(--text-2xs);
  color: var(--xl-ink-mute);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* ============================================================
   FEEDBACK & WORKED SOLUTION DRAWERS
   ============================================================ */
.feedback-box {
  border-radius: var(--radius-sm);
  padding: 0.75rem 1rem;
  font-size: var(--text-sm);
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.feedback-box.feedback-success {
  background-color: var(--xl-good-soft);
  border: 1px solid var(--xl-good);
  color: var(--xl-good);
}

.feedback-box.feedback-error {
  background-color: var(--xl-error-soft);
  border: 1px solid var(--xl-error);
  color: var(--xl-error);
}

.feedback-box.feedback-warn {
  background-color: var(--xl-warn-soft);
  border: 1px solid var(--xl-warn);
  color: var(--xl-warn);
}

.worked-solution-drawer {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin-top: 0.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.solution-header {
  font-size: var(--text-sm);
  font-weight: 700;
  color: var(--xl-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.solution-steps {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--xl-ink-soft);
  line-height: 1.6;
  white-space: pre-wrap;
  word-break: break-word;
  overflow-wrap: break-word;
}

/* Attempt Breakdown Pill in Header / Banner */
.attempt-breakdown-bar {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-family: var(--font-mono);
  font-size: var(--text-2xs);
  color: var(--xl-ink-mute);
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius-sm);
}

.attempt-stat-item {
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

.attempt-stat-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
}

.dot-try-1 { background-color: var(--xl-good); }
.dot-try-2 { background-color: var(--xl-primary); }
.dot-try-3 { background-color: var(--xl-warn); }
.dot-missed { background-color: var(--xl-error); }

/* ============================================================
   IN-SITE REFERENCE DRAWER & CALCULATOR
   ============================================================ */
.drawer-panel {
  position: fixed;
  top: 60px;
  right: -680px;
  width: 640px;
  max-width: 95vw;
  bottom: 0;
  background-color: var(--xl-surface);
  border-left: 1px solid var(--xl-border);
  z-index: 90;
  display: flex;
  flex-direction: column;
  transition: right 0.25s cubic-bezier(0.16, 1, 0.3, 1);
  box-shadow: -10px 0 25px rgba(0, 0, 0, 0.4);
}

.drawer-panel.open {
  right: 0;
}

.drawer-header {
  padding: 0.85rem 1.25rem;
  border-bottom: 1px solid var(--xl-border);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.drawer-title {
  font-size: var(--text-sm);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--xl-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.drawer-tab-bar {
  display: flex;
  background-color: var(--xl-card);
  border-bottom: 1px solid var(--xl-border);
  padding: 0 0.75rem;
}

.drawer-tab-btn {
  background: none;
  border: none;
  border-bottom: 2px solid transparent;
  color: var(--xl-ink-mute);
  font-family: var(--font-display);
  font-size: var(--text-xs);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.65rem 1rem;
  cursor: pointer;
  transition: all 0.15s;
}

.drawer-tab-btn:hover {
  color: var(--xl-ink);
}

.drawer-tab-btn.active {
  color: var(--xl-primary);
  border-bottom-color: var(--xl-primary);
}

.drawer-body {
  flex: 1;
  overflow-y: auto;
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.drawer-tab-content {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

/* Periodic Table Tooling */
.ptable-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.ptable-modes {
  display: flex;
  gap: 0.25rem;
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  padding: 2px;
}

.ptable-mode-btn {
  background: none;
  border: none;
  color: var(--xl-ink-mute);
  font-family: var(--font-mono);
  font-size: var(--text-2xs);
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  cursor: pointer;
  transition: all 0.15s;
}

.ptable-mode-btn.active {
  background-color: var(--xl-primary);
  color: #0f172a;
  font-weight: 700;
}

.ptable-check-label {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  font-size: var(--text-2xs);
  font-family: var(--font-mono);
  color: var(--xl-ink-mute);
  cursor: pointer;
}

.ptable-grid-wrapper {
  overflow-x: auto;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--xl-border-soft);
}

.ptable-grid {
  display: grid;
  grid-template-columns: repeat(18, 1fr);
  gap: 3px;
  min-width: 580px;
}

.ptable-cell {
  aspect-ratio: 1;
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: 4px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  position: relative;
  cursor: pointer;
  user-select: none;
  transition: all 0.15s;
}

.ptable-cell:hover {
  border-color: var(--xl-primary);
  transform: scale(1.1);
  z-index: 5;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.3);
}

.ptable-cell.selected {
  border-color: var(--xl-primary) !important;
  border-width: 2px !important;
  box-shadow: 0 0 0 2px var(--xl-primary-soft);
  z-index: 6;
  transform: scale(1.1);
}

.cell-z {
  font-family: var(--font-mono);
  font-size: 8px;
  color: var(--xl-ink-mute);
  position: absolute;
  top: 1px;
  left: 2px;
}

.cell-sym {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: 700;
  line-height: 1;
}

.cell-val {
  font-family: var(--font-mono);
  font-size: 7.5px;
  color: var(--xl-ink-mute);
  line-height: 1;
}

/* Category styling */
.ptable-cell.kind-metal {
  background-color: rgba(56, 189, 248, 0.08);
  border-color: rgba(56, 189, 248, 0.25);
  color: var(--xl-ink);
}

.ptable-cell.kind-metalloid {
  background-color: rgba(245, 158, 11, 0.08);
  border-color: rgba(245, 158, 11, 0.25);
  color: var(--xl-ink);
}

.ptable-cell.kind-nonmetal {
  background-color: rgba(16, 185, 129, 0.08);
  border-color: rgba(16, 185, 129, 0.25);
  color: var(--xl-ink);
}

.ptable-cell.kind-noble {
  background-color: rgba(168, 85, 247, 0.08);
  border-color: rgba(168, 85, 247, 0.25);
  color: var(--xl-ink);
}

.ptable-legend-bar {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.75rem;
  font-size: var(--text-2xs);
  font-family: var(--font-mono);
  color: var(--xl-ink-mute);
  padding: 0.25rem 0;
}

.ptable-legend-swatches {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.ptable-legend-swatch {
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

.ptable-legend-chip {
  width: 9px;
  height: 9px;
  border-radius: 2px;
}

/* Element Inspector */
.element-inspector-card {
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-md);
  padding: 1rem;
  min-height: 165px;
  display: flex;
  flex-direction: column;
}

.inspector-empty {
  margin: auto;
  font-size: var(--text-xs);
  color: var(--xl-ink-mute);
  text-align: center;
  line-height: 1.5;
}

.inspector-layout {
  display: flex;
  gap: 1.25rem;
  align-items: flex-start;
}

.inspector-main {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.inspector-header-row {
  display: flex;
  align-items: baseline;
  gap: 0.6rem;
}

.inspector-sym {
  font-family: var(--font-mono);
  font-size: var(--text-2xl);
  font-weight: 800;
  color: var(--xl-primary);
  line-height: 1;
}

.inspector-z {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--xl-ink-mute);
}

.inspector-mass {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--xl-primary);
  font-weight: 600;
  margin-left: auto;
}

.inspector-name {
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--xl-ink);
}

.inspector-kind-badge {
  display: inline-block;
  align-self: flex-start;
  font-family: var(--font-mono);
  font-size: var(--text-3xs);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 1px 6px;
  border-radius: 3px;
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  color: var(--xl-ink-soft);
}

.inspector-stats-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.35rem 0.75rem;
  margin-top: 0.4rem;
}

.inspector-stat-item {
  display: flex;
  justify-content: space-between;
  font-size: var(--text-2xs);
  font-family: var(--font-mono);
  border-bottom: 1px dashed var(--xl-border-soft);
  padding-bottom: 2px;
}

.inspector-stat-item .stat-label {
  color: var(--xl-ink-mute);
}

.inspector-stat-item .stat-value {
  color: var(--xl-ink);
  font-weight: 600;
}

.inspector-visual {
  width: 130px;
  height: 130px;
  flex-shrink: 0;
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Reference Tables */
.ref-table-block {
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  padding: 0.85rem;
}

.ref-table-title {
  font-size: var(--text-xs);
  font-weight: 700;
  color: var(--xl-ink-soft);
  text-transform: uppercase;
  margin-bottom: 0.5rem;
}

.ref-row {
  display: flex;
  justify-content: space-between;
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  padding: 0.25rem 0;
  border-bottom: 1px dashed var(--xl-border-soft);
}

/* Mini Calculator Widget */
.calc-widget {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  width: 290px;
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-lg);
  box-shadow: 0 15px 30px rgba(0, 0, 0, 0.5);
  z-index: 80;
  display: none;
  flex-direction: column;
  overflow: hidden;
}

.calc-widget.open {
  display: flex;
}

.calc-header {
  padding: 0.5rem 0.75rem;
  background-color: var(--xl-card);
  border-bottom: 1px solid var(--xl-border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: var(--text-xs);
  font-weight: 700;
  color: var(--xl-ink-soft);
  cursor: grab;
  user-select: none;
  touch-action: none;
}

.calc-header:active {
  cursor: grabbing;
}

.calc-drag-title {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.calc-drag-grip {
  font-size: 13px;
  color: var(--xl-primary);
  opacity: 0.85;
}

.calc-screen {
  padding: 0.75rem;
  background-color: #0b0f14;
  border-bottom: 1px solid var(--xl-border);
  font-family: var(--font-mono);
  text-align: right;
}

.calc-expression {
  font-size: var(--text-xs);
  color: var(--xl-ink-mute);
  min-height: 1.1rem;
}

.calc-value {
  font-size: var(--text-lg);
  font-weight: 700;
  color: var(--xl-primary);
  overflow-x: auto;
}

.calc-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 4px;
  padding: 8px;
  background-color: var(--xl-card);
}

.calc-btn {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  color: var(--xl-ink);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  padding: 0.5rem 0;
  cursor: pointer;
  transition: all 0.15s;
}

.calc-btn:hover {
  background-color: var(--xl-card-hover);
  border-color: var(--xl-primary);
}

.calc-btn-op {
  color: var(--xl-primary);
  font-weight: 600;
}

.calc-btn-eq {
  background-color: var(--xl-primary);
  color: #0f172a;
  font-weight: 700;
}

.calc-btn-eq:hover {
  background-color: #7dd3fc;
}

/* ============================================================
   MODALS (SETUP & REPORT)
   ============================================================ */
.modal-overlay {
  position: fixed;
  inset: 0;
  background-color: rgba(10, 15, 22, 0.8);
  backdrop-filter: blur(4px);
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
}

.modal-content {
  background-color: var(--xl-surface);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-lg);
  max-width: 32rem;
  width: 100%;
  padding: 2rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.5);
}

.modal-title {
  font-size: var(--text-xl);
  font-weight: 800;
  color: var(--xl-ink);
}

.modal-subtitle {
  font-size: var(--text-sm);
  color: var(--xl-ink-mute);
}

.modal-input {
  background-color: var(--xl-card);
  border: 1px solid var(--xl-border);
  border-radius: var(--radius-sm);
  color: var(--xl-ink);
  font-family: var(--font-display);
  font-size: var(--text-base);
  padding: 0.75rem 1rem;
  outline: none;
}

.modal-input:focus {
  border-color: var(--xl-primary);
}

/* ============================================================
   STRICT SINGLE A4 PAGE PRINT LAYOUT
   ============================================================ */
#studyReportSheet {
  display: none;
}

@page {
  size: A4 portrait;
  margin: 6mm 8mm;
}

@media print {
  body {
    background: #ffffff !important;
    color: #000000 !important;
    font-size: 8pt !important;
    line-height: 1.2 !important;
    margin: 0 !important;
    padding: 0 !important;
  }

  .station-header,
  .unit-banner,
  .input-zone,
  .btn,
  .modal-overlay,
  .problem-card,
  .drawer-panel,
  .calc-widget {
    display: none !important;
  }

  #studyReportSheet {
    display: block !important;
    width: 100% !important;
    margin: 0 !important;
    padding: 0 !important;
  }

  .print-receipt-header {
    border-bottom: 1.5pt solid #000;
    padding-bottom: 4pt;
    margin-bottom: 6pt;
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 8pt;
  }

  .print-title-area h2 {
    font-size: 13pt;
    font-weight: 900;
    margin: 0;
    text-transform: uppercase;
    letter-spacing: -0.01em;
  }

  .print-title-area p {
    font-size: 8pt;
    color: #333;
    margin: 2pt 0 0 0;
  }

  .print-header-center {
    text-align: center;
    border: 1pt solid #000;
    padding: 4pt 8pt;
    border-radius: 3pt;
    background-color: #f8fafc;
  }

  .print-big-score {
    font-size: 13pt;
    font-weight: 900;
    line-height: 1;
  }

  .print-attempt-pill {
    font-size: 7.5pt;
    font-family: var(--font-mono);
    margin-top: 2pt;
    color: #222;
  }

  .print-seal-container {
    display: flex;
    align-items: center;
    gap: 6pt;
    border: 1pt solid #000;
    padding: 3pt 6pt;
    border-radius: 3pt;
  }

  .print-qr-code {
    width: 52px;
    height: 52px;
  }

  .print-seal-meta {
    font-family: var(--font-mono);
    font-size: 7pt;
    text-align: right;
  }

  .print-seal-code {
    font-size: 9pt;
    font-weight: 900;
    letter-spacing: 0.05em;
  }

  /* 2-Column Grid for the 6 Problems */
  .print-problems-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 5pt 7pt;
    margin-bottom: 4pt;
  }

  .print-problem-card {
    border: 0.75pt solid #888;
    border-radius: 3pt;
    padding: 4pt 6pt;
    background-color: #ffffff;
    display: flex;
    flex-direction: column;
    gap: 2pt;
    page-break-inside: avoid;
  }

  .print-card-top {
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 0.5pt solid #ccc;
    padding-bottom: 2pt;
  }

  .print-card-num {
    font-weight: 800;
    font-size: 7.5pt;
    text-transform: uppercase;
  }

  .print-card-status {
    font-family: var(--font-mono);
    font-size: 6.5pt;
    font-weight: 700;
    padding: 1pt 3pt;
    border-radius: 2pt;
  }

  .status-tag-solved {
    background-color: #d1fae5;
    color: #065f46;
  }

  .status-tag-exhausted {
    background-color: #fee2e2;
    color: #991b1b;
  }

  .print-card-stem {
    font-size: 7pt;
    color: #222;
    line-height: 1.15;
  }

  .print-card-response {
    font-family: var(--font-mono);
    font-size: 7pt;
    color: #111;
  }

  .print-card-solution {
    font-family: var(--font-mono);
    font-size: 6.5pt;
    line-height: 1.15;
    background-color: #f1f5f9;
    border-left: 2pt solid #2563eb;
    padding: 2pt 4pt;
    white-space: pre-wrap;
    word-break: break-word;
    color: #1e293b;
  }

  /* Curriculum Skill Mastery Scorecard */
  .print-scorecard-section {
    margin: 3pt 0 4pt 0;
  }

  .print-scorecard-title {
    font-size: 6.8pt;
    font-weight: 800;
    text-transform: uppercase;
    letter-spacing: 0.04em;
    color: #0f172a;
    margin-bottom: 2pt;
    border-bottom: 0.5pt solid #cbd5e1;
    padding-bottom: 1pt;
  }

  .print-scorecard-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 2.5pt 4pt;
  }

  .print-skill-card {
    border: 0.5pt solid #cbd5e1;
    border-radius: 2pt;
    padding: 1.5pt 3pt;
    background-color: #ffffff;
    display: flex;
    flex-direction: column;
    gap: 0.75pt;
  }

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

  .print-skill-num {
    font-size: 5.5pt;
    font-weight: 700;
    color: #475569;
    font-family: var(--font-mono);
  }

  .print-skill-status {
    font-size: 5.2pt;
    font-weight: 700;
    font-family: var(--font-mono);
    padding: 0.5pt 1.5pt;
    border-radius: 1.5pt;
  }

  .tag-mastered {
    background-color: #d1fae5;
    color: #065f46;
  }

  .tag-developing {
    background-color: #fef3c7;
    color: #92400e;
  }

  .tag-needs-work {
    background-color: #fee2e2;
    color: #991b1b;
  }

  .print-skill-name {
    font-size: 5.9pt;
    font-weight: 600;
    color: #0f172a;
    line-height: 1.15;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
  }

  .print-skill-guide {
    font-size: 5.5pt;
    font-family: var(--font-mono);
    color: #334155;
  }

  .study-rec {
    color: #b45309;
    font-weight: 600;
  }

  .study-mastered {
    color: #059669;
  }

  /* Compact 16-Row Matrix Table for Single A4 Page Guarantee */
  .print-matrix-table {
    width: 100%;
    border-collapse: collapse;
    margin: 3pt 0 4pt 0;
    font-size: 6.4pt;
  }

  .print-matrix-table th {
    background-color: #f1f5f9;
    border: 0.5pt solid #64748b;
    padding: 1.8pt 3pt;
    text-align: left;
    font-family: var(--font-mono);
    font-size: 5.8pt;
    font-weight: 700;
    text-transform: uppercase;
    color: #0f172a;
  }

  .print-matrix-table td {
    border: 0.5pt solid #cbd5e1;
    padding: 1.8pt 3pt;
    line-height: 1.15;
    vertical-align: middle;
    color: #111;
  }

  .print-matrix-table tr:nth-child(even) td {
    background-color: #f8fafc;
  }

  .print-matrix-status {
    display: inline-block;
    font-family: var(--font-mono);
    font-size: 5.6pt;
    font-weight: 700;
    padding: 0.5pt 2pt;
    border-radius: 2pt;
  }

  .print-receipt-footer {
    border-top: 0.5pt solid #000;
    padding-top: 2pt;
    display: flex;
    justify-content: space-between;
    font-size: 6.2pt;
    color: #555;
  }
}