/* ============================================================
   SparkMath — Grade 3 Worksheet Generator
   Design: Friendly / Playful / Education
   Fonts: Chillax (display) + Nunito (body)
   ============================================================ */

/* ── Design Tokens ── */
:root,
[data-theme='light'] {
  /* Surfaces */
  --color-bg: #f5f3ff;
  --color-surface: #ffffff;
  --color-surface-2: #f9f8ff;
  --color-surface-offset: #ede9fe;
  --color-border: #ddd6fe;
  --color-divider: #e5e0fd;

  /* Text */
  --color-text: #1e1b4b;
  --color-text-muted: #6b6b99;
  --color-text-faint: #a5b4fc;
  --color-text-inverse: #ffffff;

  /* Primary (Purple) */
  --color-primary: #6d28d9;
  --color-primary-hover: #5b21b6;
  --color-primary-active: #4c1d95;
  --color-primary-light: #ede9fe;

  /* Accent colors */
  --color-accent-1: #f59e0b;   /* Gold/amber */
  --color-accent-2: #ec4899;   /* Pink */
  --color-accent-3: #10b981;   /* Green */
  --color-accent-4: #3b82f6;   /* Blue */

  /* Op colors */
  --color-add: #10b981;
  --color-sub: #3b82f6;
  --color-mul: #f59e0b;
  --color-div: #ec4899;
  --color-mix: #6d28d9;

  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(109,40,217,0.08);
  --shadow-md: 0 4px 16px rgba(109,40,217,0.1);
  --shadow-lg: 0 12px 40px rgba(109,40,217,0.14);

  /* Radius */
  --radius-sm: 0.5rem;
  --radius-md: 0.75rem;
  --radius-lg: 1rem;
  --radius-xl: 1.5rem;
  --radius-full: 9999px;

  /* Type scale */
  --text-xs: clamp(0.75rem, 0.7rem + 0.25vw, 0.875rem);
  --text-sm: clamp(0.875rem, 0.8rem + 0.35vw, 1rem);
  --text-base: clamp(1rem, 0.95rem + 0.25vw, 1.125rem);
  --text-lg: clamp(1.125rem, 1rem + 0.75vw, 1.5rem);
  --text-xl: clamp(1.5rem, 1.2rem + 1.25vw, 2.25rem);
  --text-2xl: clamp(2rem, 1.2rem + 2.5vw, 3.5rem);

  /* Spacing */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;

  /* Fonts */
  --font-display: 'Chillax', 'Nunito', sans-serif;
  --font-body: 'Nunito', 'Segoe UI', sans-serif;

  --transition-interactive: 180ms cubic-bezier(0.16, 1, 0.3, 1);
  --content-default: 1200px;
}

[data-theme='dark'] {
  --color-bg: #13111f;
  --color-surface: #1c1a2e;
  --color-surface-2: #221f37;
  --color-surface-offset: #2a2745;
  --color-border: #3a3660;
  --color-divider: #302d52;
  --color-text: #e2e0ff;
  --color-text-muted: #9390c0;
  --color-text-faint: #5a5880;
  --color-text-inverse: #13111f;
  --color-primary: #a78bfa;
  --color-primary-hover: #c4b5fd;
  --color-primary-active: #ddd6fe;
  --color-primary-light: #2d2860;

  --color-add: #34d399;
  --color-sub: #60a5fa;
  --color-mul: #fbbf24;
  --color-div: #f472b6;
  --color-mix: #a78bfa;

  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.4);
  --shadow-lg: 0 12px 40px rgba(0,0,0,0.5);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme]) {
    --color-bg: #13111f;
    --color-surface: #1c1a2e;
    --color-surface-2: #221f37;
    --color-surface-offset: #2a2745;
    --color-border: #3a3660;
    --color-divider: #302d52;
    --color-text: #e2e0ff;
    --color-text-muted: #9390c0;
    --color-text-faint: #5a5880;
    --color-text-inverse: #13111f;
    --color-primary: #a78bfa;
    --color-primary-hover: #c4b5fd;
    --color-primary-active: #ddd6fe;
    --color-primary-light: #2d2860;
    --color-add: #34d399;
    --color-sub: #60a5fa;
    --color-mul: #fbbf24;
    --color-div: #f472b6;
    --color-mix: #a78bfa;
    --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
    --shadow-md: 0 4px 16px rgba(0,0,0,0.4);
    --shadow-lg: 0 12px 40px rgba(0,0,0,0.5);
  }
}

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

html {
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  scroll-behavior: smooth;
  scroll-padding-top: var(--space-16);
}

body {
  min-height: 100dvh;
  line-height: 1.6;
  font-family: var(--font-body);
  font-size: var(--text-base);
  color: var(--color-text);
  background-color: var(--color-bg);
  transition: background-color 0.3s ease, color 0.3s ease;
}

img, picture, video, canvas, svg { display: block; max-width: 100%; }
input, button, textarea, select { font: inherit; color: inherit; }
h1, h2, h3, h4, h5, h6 { text-wrap: balance; line-height: 1.2; }
p, li { text-wrap: pretty; }
button { cursor: pointer; background: none; border: none; }

::selection {
  background: color-mix(in oklab, var(--color-primary) 25%, transparent);
  color: var(--color-text);
}

:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 3px;
  border-radius: var(--radius-sm);
}

/* ── Header ── */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: color-mix(in oklab, var(--color-surface) 85%, transparent);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--color-divider);
  padding: var(--space-3) var(--space-6);
  transition: background 0.3s ease;
}

.header-inner {
  max-width: var(--content-default);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  text-decoration: none;
  color: var(--color-text);
}

.logo-icon { color: var(--color-primary); flex-shrink: 0; }

.logo-text {
  font-family: var(--font-display);
  font-size: var(--text-lg);
  font-weight: 700;
  letter-spacing: -0.01em;
}

.logo-accent { color: var(--color-primary); }

.btn-icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  transition: all var(--transition-interactive);
}

.btn-icon:hover {
  color: var(--color-primary);
  border-color: var(--color-primary);
  background: var(--color-primary-light);
}

/* ── Hero ── */
.hero {
  position: relative;
  overflow: hidden;
  padding: var(--space-12) var(--space-6) var(--space-8);
  background: linear-gradient(135deg in oklab,
    var(--color-primary-light) 0%,
    var(--color-bg) 60%
  );
}

.hero-inner {
  max-width: var(--content-default);
  margin: 0 auto;
  position: relative;
  z-index: 2;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  font-weight: 700;
  color: var(--color-primary);
  background: var(--color-primary-light);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-full);
  padding: var(--space-1) var(--space-4);
  margin-bottom: var(--space-5);
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

.hero-title {
  font-family: var(--font-display);
  font-size: var(--text-2xl);
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: var(--space-4);
  line-height: 1.1;
}

.highlight {
  color: var(--color-primary);
  position: relative;
  display: inline-block;
}

.highlight::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  right: 0;
  height: 6px;
  background: linear-gradient(90deg, var(--color-accent-1), var(--color-accent-2));
  border-radius: 99px;
  opacity: 0.7;
}

.hero-sub {
  font-size: var(--text-lg);
  color: var(--color-text-muted);
  max-width: 52ch;
}

/* Floating math shapes */
.hero-shapes { position: absolute; inset: 0; pointer-events: none; overflow: hidden; z-index: 1; }

.shape {
  position: absolute;
  font-family: var(--font-display);
  font-weight: 700;
  opacity: 0.08;
  animation: float linear infinite;
  color: var(--color-primary);
  line-height: 1;
  user-select: none;
}

[data-theme='dark'] .shape { opacity: 0.12; }

.shape-1 { font-size: 96px; top: -10%; right: 8%; animation-duration: 18s; animation-delay: 0s; }
.shape-2 { font-size: 72px; top: 20%; right: 22%; animation-duration: 14s; animation-delay: -5s; }
.shape-3 { font-size: 60px; bottom: -5%; right: 35%; animation-duration: 22s; animation-delay: -10s; }
.shape-4 { font-size: 80px; top: 5%; right: 48%; animation-duration: 16s; animation-delay: -3s; }
.shape-5 { font-size: 110px; bottom: -10%; right: 5%; animation-duration: 20s; animation-delay: -7s; }

@keyframes float {
  0%, 100% { transform: translateY(0) rotate(0deg); }
  25% { transform: translateY(-12px) rotate(3deg); }
  75% { transform: translateY(8px) rotate(-2deg); }
}

/* ── Main Layout ── */
.main-content {
  padding: var(--space-8) var(--space-6) var(--space-16);
}

.container {
  max-width: var(--content-default);
  margin: 0 auto;
  display: grid;
  grid-template-columns: 380px 1fr;
  gap: var(--space-8);
  align-items: start;
}

@media (max-width: 900px) {
  .container { grid-template-columns: 1fr; }
}

/* ── Panels ── */
.controls-panel,
.preview-panel {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-xl);
  padding: var(--space-6);
  box-shadow: var(--shadow-md);
  transition: background 0.3s ease, border-color 0.3s ease;
}

.panel-title {
  font-family: var(--font-display);
  font-size: var(--text-lg);
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: var(--space-5);
}

/* ── Control Groups ── */
.control-group { margin-bottom: var(--space-6); }

.control-label {
  display: block;
  font-size: var(--text-sm);
  font-weight: 700;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: var(--space-3);
}

/* ── Operation Buttons ── */
.operation-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-2);
}

.op-btn-wide {
  grid-column: 1 / -1;
}

.op-btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-3) var(--space-2);
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  background: var(--color-surface-2, var(--color-bg));
  color: var(--color-text-muted);
  transition: all var(--transition-interactive);
  font-family: var(--font-body);
}

.op-btn:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.op-btn.active {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
  color: var(--color-primary);
}

.op-symbol {
  font-family: var(--font-display);
  font-size: var(--text-xl);
  font-weight: 700;
  line-height: 1;
}

.op-name {
  font-size: var(--text-xs);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Op-specific colors when active */
.op-btn[data-op="addition"].active { --color-primary: var(--color-add); --color-primary-light: #d1fae5; }
.op-btn[data-op="subtraction"].active { --color-primary: var(--color-sub); --color-primary-light: #dbeafe; }
.op-btn[data-op="multiplication"].active { --color-primary: var(--color-mul); --color-primary-light: #fef3c7; }
.op-btn[data-op="division"].active { --color-primary: var(--color-div); --color-primary-light: #fce7f3; }

[data-theme='dark'] .op-btn[data-op="addition"].active { --color-primary-light: #064e3b; }
[data-theme='dark'] .op-btn[data-op="subtraction"].active { --color-primary-light: #1e3a5f; }
[data-theme='dark'] .op-btn[data-op="multiplication"].active { --color-primary-light: #78350f; }
[data-theme='dark'] .op-btn[data-op="division"].active { --color-primary-light: #831843; }

/* ── Difficulty Buttons ── */
.difficulty-grid {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr;
  gap: var(--space-2);
}

@media (max-width: 480px) {
  .difficulty-grid {
    grid-template-columns: 1fr 1fr;
  }
}

.diff-btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-3) var(--space-2);
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text-muted);
  transition: all var(--transition-interactive);
  text-align: center;
}

.diff-btn:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.diff-btn.active {
  border-color: var(--color-primary);
  background: var(--color-primary-light);
  color: var(--color-primary);
}

/* Expert difficulty — deep violet/indigo accent */
.diff-btn--expert {
  border-color: #7c3aed33;
  background: linear-gradient(135deg, #f5f3ff 0%, #ede9fe 100%);
  color: #5b21b6;
}
[data-theme='dark'] .diff-btn--expert {
  background: linear-gradient(135deg, #1e1030 0%, #2e1a5e 100%);
  color: #c4b5fd;
  border-color: #7c3aed55;
}
.diff-btn--expert:hover,
.diff-btn--expert.active {
  border-color: #7c3aed;
  background: linear-gradient(135deg, #ede9fe 0%, #ddd6fe 100%);
  color: #5b21b6;
  box-shadow: 0 0 0 3px #7c3aed22;
}
[data-theme='dark'] .diff-btn--expert:hover,
[data-theme='dark'] .diff-btn--expert.active {
  border-color: #c4b5fd;
  background: linear-gradient(135deg, #2e1a5e 0%, #3b1f7a 100%);
  color: #ede9fe;
}

.diff-emoji { font-size: var(--text-lg); line-height: 1; }
.diff-name { font-size: var(--text-sm); font-weight: 700; }
.diff-desc { font-size: var(--text-xs); color: var(--color-text-faint); }

/* ── Count Control ── */
.count-control {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.count-btn {
  width: 42px;
  height: 42px;
  border-radius: var(--radius-full);
  border: 2px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text);
  font-size: var(--text-lg);
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-interactive);
  flex-shrink: 0;
}

.count-btn:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background: var(--color-primary-light);
}

#problemCount {
  width: 80px;
  text-align: center;
  font-size: var(--text-lg);
  font-weight: 700;
  font-family: var(--font-display);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text);
  transition: border-color var(--transition-interactive);
  -moz-appearance: textfield;
}

#problemCount::-webkit-inner-spin-button,
#problemCount::-webkit-outer-spin-button { -webkit-appearance: none; }

#problemCount:focus { border-color: var(--color-primary); outline: none; }

/* ── Options / Checkboxes ── */
.options-list { display: flex; flex-direction: column; gap: var(--space-3); }

.checkbox-label {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  cursor: pointer;
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-text);
  user-select: none;
}

.checkbox-label input[type="checkbox"] { position: absolute; opacity: 0; width: 0; height: 0; }

.checkbox-box {
  width: 22px;
  height: 22px;
  border-radius: var(--radius-sm);
  border: 2px solid var(--color-border);
  background: var(--color-bg);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  transition: all var(--transition-interactive);
  position: relative;
}

.checkbox-label input[type="checkbox"]:checked + .checkbox-box {
  background: var(--color-primary);
  border-color: var(--color-primary);
}

.checkbox-label input[type="checkbox"]:checked + .checkbox-box::after {
  content: '';
  width: 12px;
  height: 7px;
  border-left: 2.5px solid white;
  border-bottom: 2.5px solid white;
  transform: rotate(-45deg) translateY(-1px);
  display: block;
}

/* ── Text Input ── */
.text-input {
  width: 100%;
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text);
  font-size: var(--text-base);
  transition: border-color var(--transition-interactive);
}

.text-input:focus { border-color: var(--color-primary); outline: none; }
.text-input::placeholder { color: var(--color-text-faint); }

/* ── Generate Button ── */
.btn-generate {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-4) var(--space-6);
  border-radius: var(--radius-lg);
  background: var(--color-primary);
  color: white;
  font-family: var(--font-display);
  font-size: var(--text-base);
  font-weight: 700;
  letter-spacing: 0.01em;
  transition: all var(--transition-interactive);
  box-shadow: 0 4px 20px color-mix(in oklab, var(--color-primary) 40%, transparent);
  border: none;
}

.btn-generate:hover {
  background: var(--color-primary-hover);
  transform: translateY(-2px);
  box-shadow: 0 8px 24px color-mix(in oklab, var(--color-primary) 45%, transparent);
}

.btn-generate:active { transform: translateY(0); }

/* ── Preview Panel ── */
.preview-panel { min-height: 400px; }

.preview-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--space-5);
  gap: var(--space-3);
  flex-wrap: wrap;
}

.preview-header .panel-title { margin-bottom: 0; }

.preview-actions {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
}

.btn-action {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-md);
  border: 2px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text);
  font-size: var(--text-sm);
  font-weight: 700;
  transition: all var(--transition-interactive);
}

.btn-action:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.btn-action.btn-primary {
  background: var(--color-primary);
  border-color: var(--color-primary);
  color: white;
}

.btn-action.btn-primary:hover {
  background: var(--color-primary-hover);
  border-color: var(--color-primary-hover);
  color: white;
}

/* ── Empty State ── */
.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: var(--space-16) var(--space-8);
  gap: var(--space-3);
  color: var(--color-text-faint);
}

.empty-icon { margin-bottom: var(--space-2); }
.empty-title { font-size: var(--text-base); font-weight: 700; color: var(--color-text-muted); }
.empty-sub { font-size: var(--text-sm); max-width: 36ch; }

/* ── Worksheet ── */
.worksheet {
  padding: var(--space-6) var(--space-4);
}

.ws-header {
  margin-bottom: var(--space-6);
  padding-bottom: var(--space-4);
  border-bottom: 2px dashed var(--color-divider);
}

.ws-title {
  font-family: var(--font-display);
  font-size: var(--text-xl);
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: var(--space-4);
}

.ws-meta {
  display: flex;
  gap: var(--space-8);
  flex-wrap: wrap;
}

.ws-field {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
}

.ws-field-label {
  font-size: var(--text-xs);
  font-weight: 700;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.ws-field-line {
  width: 180px;
  height: 2px;
  background: var(--color-border);
  border-radius: 99px;
}

.ws-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  font-size: var(--text-xs);
  font-weight: 700;
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-full);
  border: 1.5px solid currentColor;
  margin-bottom: var(--space-3);
}

.ws-badge.add { color: var(--color-add); background: color-mix(in oklab, var(--color-add) 12%, transparent); }
.ws-badge.sub { color: var(--color-sub); background: color-mix(in oklab, var(--color-sub) 12%, transparent); }
.ws-badge.mul { color: var(--color-mul); background: color-mix(in oklab, var(--color-mul) 12%, transparent); }
.ws-badge.div { color: var(--color-div); background: color-mix(in oklab, var(--color-div) 12%, transparent); }
.ws-badge.mix { color: var(--color-mix); background: color-mix(in oklab, var(--color-mix) 12%, transparent); }

/* ── Equation Grid ── */
.equations-grid {
  display: grid;
  gap: var(--space-3);
}

.equations-grid.two-col {
  grid-template-columns: 1fr 1fr;
}

@media (max-width: 600px) {
  .equations-grid.two-col { grid-template-columns: 1fr; }
}

.equation-item {
  display: flex;
  flex-direction: column;
  padding: var(--space-3) var(--space-4);
  background: var(--color-bg);
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-md);
  font-family: var(--font-display);
  font-size: var(--text-base);
  font-weight: 600;
  color: var(--color-text);
  transition: border-color var(--transition-interactive);
  gap: var(--space-2);
}

.equation-item:hover { border-color: var(--color-primary); }

.eq-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.eq-number {
  font-size: var(--text-xs);
  font-weight: 700;
  color: var(--color-text-faint);
  min-width: 1.5em;
  text-align: right;
  flex-shrink: 0;
}

.eq-expression {
  flex: 1;
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex-wrap: wrap;
}

.eq-num { color: var(--color-text); }
.eq-op {
  font-weight: 800;
  font-size: var(--text-lg);
  width: 1.4em;
  text-align: center;
}
.eq-op.op-add { color: var(--color-add); }
.eq-op.op-sub { color: var(--color-sub); }
.eq-op.op-mul { color: var(--color-mul); }
.eq-op.op-div { color: var(--color-div); }

.eq-equals { color: var(--color-text-muted); font-size: var(--text-lg); }

.eq-answer-line {
  display: inline-block;
  width: 60px;
  height: 1.1em;
  border-bottom: 2px solid var(--color-border);
  vertical-align: bottom;
  margin-left: var(--space-1);
}

.eq-answer {
  font-size: var(--text-sm);
  font-weight: 700;
  color: var(--color-primary);
  min-width: 60px;
}

/* Answer key section */
.answer-key {
  margin-top: var(--space-8);
  padding-top: var(--space-6);
  border-top: 2px dashed var(--color-divider);
}

.answer-key-title {
  font-family: var(--font-display);
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: var(--space-4);
}

.answer-key-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(100px, 1fr));
  gap: var(--space-2);
}

.answer-item {
  font-size: var(--text-sm);
  font-family: var(--font-display);
  font-weight: 700;
  display: flex;
  gap: var(--space-2);
}

.answer-item .ans-num { color: var(--color-text-muted); }
.answer-item .ans-val { color: var(--color-primary); }

/* ── Footer ── */
.site-footer {
  text-align: center;
  padding: var(--space-6);
  border-top: 1px solid var(--color-divider);
  font-size: var(--text-xs);
  color: var(--color-text-faint);
}

/* ── Language Switcher ── */
.lang-switcher {
  position: relative;
}

.lang-current {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-full);
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text);
  font-size: var(--text-sm);
  font-weight: 700;
  cursor: pointer;
  transition: all var(--transition-interactive);
  white-space: nowrap;
}

.lang-current:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  background: var(--color-primary-light);
}

.lang-dropdown {
  position: absolute;
  top: calc(100% + var(--space-2));
  right: 0;
  background: var(--color-surface);
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  padding: var(--space-2);
  display: flex;
  flex-direction: column;
  gap: 2px;
  min-width: 140px;
  z-index: 200;
  animation: slideInUp 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

.lang-dropdown[hidden] {
  display: none;
}

.lang-btn {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-md);
  border: none;
  background: none;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  font-weight: 600;
  cursor: pointer;
  text-align: left;
  transition: all var(--transition-interactive);
  width: 100%;
}

.lang-btn:hover {
  background: var(--color-surface-offset, var(--color-bg));
  color: var(--color-text);
}

.lang-btn.active {
  background: var(--color-primary-light);
  color: var(--color-primary);
  font-weight: 700;
}

/* ── Mobile Layout (<= 480px) ── */
@media (max-width: 480px) {
  /* Panel: tighter padding so worksheet gets more room */
  .controls-panel,
  .preview-panel {
    padding: var(--space-4) var(--space-3);
    border-radius: var(--radius-lg);
  }

  /* Worksheet inner padding */
  .worksheet {
    padding: var(--space-4) var(--space-3);
  }

  /* Equation grid: smaller gap */
  .equations-grid {
    gap: var(--space-2);
  }

  /* Equation card: tighter padding */
  .equation-item {
    padding: var(--space-2) var(--space-3);
    gap: var(--space-1);
    font-size: var(--text-sm);
  }

  /* Expression: tighten internal spacing */
  .eq-expression {
    gap: var(--space-1);
  }

  .eq-op {
    font-size: var(--text-base);
    width: 1.2em;
  }

  .eq-equals {
    font-size: var(--text-base);
  }

  /* Answer input: narrower on small screens */
  .eq-input {
    width: 60px;
    min-width: 48px;
    font-size: var(--text-base);
  }

  /* Work textarea: shorter default height */
  .work-textarea {
    min-height: 48px;
  }

  /* Worksheet header meta row */
  .ws-meta {
    gap: var(--space-4);
  }

  .ws-field-line {
    width: 120px;
  }

  .ws-title {
    font-size: var(--text-lg);
    margin-bottom: var(--space-3);
  }

  .ws-header {
    margin-bottom: var(--space-4);
    padding-bottom: var(--space-3);
  }

  /* Preview panel title */
  .panel-title {
    font-size: var(--text-base);
    margin-bottom: var(--space-3);
  }

  /* Preview toolbar: shrink button text, tighter gaps */
  .preview-actions {
    gap: var(--space-2);
  }

  .btn-action span {
    display: none;
  }

  .btn-action svg {
    margin: 0;
  }
}

@media print {
  .lang-switcher { display: none !important; }
}

/* ── Install Banner ── */
.install-banner {
  position: fixed;
  bottom: var(--space-4);
  left: 50%;
  transform: translateX(-50%);
  width: calc(100% - var(--space-8));
  max-width: 480px;
  display: flex;
  align-items: center;
  gap: var(--space-3);
  background: var(--color-surface);
  border: 1.5px solid var(--color-primary);
  border-radius: var(--radius-xl);
  padding: var(--space-3) var(--space-4);
  box-shadow: var(--shadow-lg);
  z-index: 999;
  animation: slideInUp 0.35s cubic-bezier(0.16, 1, 0.3, 1);
}

.install-banner-icon {
  color: var(--color-primary);
  flex-shrink: 0;
  display: flex;
  align-items: center;
}

.install-banner-text {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 2px;
  min-width: 0;
}

.install-banner-text strong {
  font-size: var(--text-sm);
  font-weight: 800;
  font-family: var(--font-display);
  color: var(--color-text);
}

.install-banner-text span {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
  line-height: 1.4;
}

.install-banner-btn {
  flex-shrink: 0;
  background: var(--color-primary);
  color: white;
  border: none;
  border-radius: var(--radius-md);
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-xs);
  font-weight: 700;
  font-family: var(--font-body);
  cursor: pointer;
  white-space: nowrap;
  transition: background var(--transition-interactive);
}

.install-banner-btn:hover { background: var(--color-primary-hover); }

.install-banner-close {
  flex-shrink: 0;
  width: 28px;
  height: 28px;
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
  background: none;
  border: none;
  cursor: pointer;
  transition: color var(--transition-interactive);
}

.install-banner-close:hover { color: var(--color-text); }

@media print {
  .install-banner, #installBanner { display: none !important; }
}

/* ── Print Styles ── */
@media print {
  /* Force light theme, no colour ink wasted on backgrounds */
  * {
    -webkit-print-color-adjust: exact !important;
    print-color-adjust: exact !important;
    color: black !important;
    background: white !important;
    box-shadow: none !important;
    text-shadow: none !important;
  }

  /* Force light mode regardless of system/user preference */
  [data-theme='dark'],
  [data-theme='dark'] * {
    color: black !important;
    background: white !important;
  }

  /* Hide everything except the worksheet */
  .site-header,
  .hero,
  .controls-panel,
  .preview-header,
  .preview-actions,
  .site-footer,
  .empty-state,
  .print-area { display: none !important; }

  html, body {
    background: white !important;
    font-size: 13pt;
    font-family: Arial, Helvetica, sans-serif;
  }

  .main-content { padding: 0 !important; }

  .container {
    display: block !important;
    max-width: none !important;
    padding: 0 !important;
  }

  .preview-panel {
    border: none !important;
    padding: 0 !important;
    border-radius: 0 !important;
  }

  .worksheet { padding: 0 !important; }

  /* ── Worksheet header ── */
  .ws-header {
    border-bottom: 1.5px solid #888 !important;
    margin-bottom: 1.2rem !important;
    padding-bottom: 0.75rem !important;
  }

  .ws-title {
    font-size: 16pt !important;
    font-weight: bold !important;
    color: black !important;
  }

  .ws-badge {
    border: 1px solid #555 !important;
    color: #333 !important;
    background: none !important;
    font-size: 9pt !important;
    padding: 2px 8px !important;
  }

  .ws-field-label { color: #444 !important; font-size: 8pt !important; }

  .ws-field-line {
    height: 1px !important;
    background: #888 !important;
    border-radius: 0 !important;
  }

  /* ── Equations grid — always 2 columns in print ── */
  .equations-grid {
    gap: 0.6rem !important;
    display: grid !important;
    grid-template-columns: 1fr 1fr !important;
  }

  .equation-item {
    background: white !important;
    border: 1px solid #ccc !important;
    border-radius: 4px !important;
    break-inside: avoid;
    page-break-inside: avoid;
    padding: 0.4rem 0.6rem !important;
    gap: 0.2rem !important;
    /* Always column layout so workspace sits below equation */
    display: flex !important;
    flex-direction: column !important;
    align-items: stretch !important;
  }

  /* All op symbols: black, no colour ink */
  .eq-op { color: black !important; font-weight: 800 !important; }
  .eq-num { color: black !important; }
  .eq-equals { color: #555 !important; }
  .eq-number { color: #888 !important; font-size: 9pt !important; }
  .eq-paren { color: #444 !important; }
  .eq-note { color: #666 !important; font-size: 8pt !important; }

  /* Answer line — clean underline at baseline */
  .eq-answer-line {
    border-bottom: 1.5px solid #555 !important;
    width: 56px !important;
  }

  /* Answer value (when answer key shown) */
  .eq-answer { color: #333 !important; font-weight: bold !important; }

  /* ── Work space ── */
  .work-space {
    margin-left: 0 !important;
    margin-top: 0.3rem !important;
  }

  /* Always show work-space in print, even if hidden on screen */
  .work-space { display: block !important; }
  .work-textarea { display: none !important; }

  .work-lines {
    gap: 0 !important;
    border: 1px solid #ddd !important;
    border-radius: 3px !important;
    padding: 4px 6px !important;
    background: white !important;
    /* Fixed tall work area: ~175px */
    min-height: 175px !important;
    display: flex !important;
    flex-direction: column !important;
    justify-content: space-between !important;
  }

  .work-line {
    flex: 1 !important;
    border-bottom: 1px dotted #ccc !important;
    background: none !important;
    min-height: 22px !important;
  }

  .work-line:last-child { border-bottom: none !important; }

  .equation-item.with-workspace {
    padding: 0.4rem 0.6rem 0.4rem !important;
  }

  .eq-row { gap: 0.2rem !important; }

  /* ── Challenge note ── */
  .challenge-note {
    color: #333 !important;
    background: none !important;
    border: 1px solid #999 !important;
    font-size: 9pt !important;
  }

  /* ── Answer key ── */
  .answer-key { border-top: 1px solid #bbb !important; margin-top: 1.5rem !important; }
  .answer-key-title { color: #333 !important; font-size: 9pt !important; }
  .answer-item .ans-num { color: #666 !important; }
  .answer-item .ans-val { color: #000 !important; font-weight: bold !important; }
  #shareSheetBtn, #shareAppBtn, .share-tooltip { display: none !important; }
}

/* ── Share tooltip ── */
.share-tooltip {
  position: fixed;
  bottom: var(--space-8);
  left: 50%;
  transform: translateX(-50%) translateY(8px);
  background: var(--color-text);
  color: var(--color-bg);
  font-size: var(--text-sm);
  font-weight: 600;
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-full);
  pointer-events: none;
  opacity: 0;
  transition: opacity 0.2s ease, transform 0.2s ease;
  z-index: 9999;
  white-space: nowrap;
}

.share-tooltip.visible {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* ── Challenge button ── */
.op-btn-challenge {
  background: linear-gradient(135deg in oklab,
    color-mix(in oklab, #0891b2 15%, var(--color-bg)),
    color-mix(in oklab, #6d28d9 15%, var(--color-bg))
  );
  border-color: color-mix(in oklab, #0891b2 40%, var(--color-border));
}

.op-btn-challenge:hover,
.op-btn-challenge.active {
  border-color: #0891b2;
  color: #0891b2;
  background: linear-gradient(135deg in oklab,
    color-mix(in oklab, #0891b2 18%, var(--color-bg)),
    color-mix(in oklab, #6d28d9 18%, var(--color-bg))
  );
}

[data-theme='dark'] .op-btn-challenge {
  border-color: color-mix(in oklab, #22d3ee 30%, var(--color-border));
}
[data-theme='dark'] .op-btn-challenge.active {
  border-color: #22d3ee;
  color: #22d3ee;
}

/* Challenge badge */
.ws-badge.cha { color: #0891b2; background: color-mix(in oklab, #0891b2 12%, transparent); border-color: #0891b2; }

/* Challenge note banner */
.challenge-note {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: #0891b2;
  background: color-mix(in oklab, #0891b2 8%, transparent);
  border: 1.5px solid color-mix(in oklab, #0891b2 30%, transparent);
  border-radius: var(--radius-md);
  padding: var(--space-3) var(--space-4);
  margin-bottom: var(--space-5);
  font-weight: 600;
}
[data-theme='dark'] .challenge-note {
  color: #22d3ee;
  background: color-mix(in oklab, #0891b2 12%, transparent);
  border-color: color-mix(in oklab, #0891b2 35%, transparent);
}

/* Equation paren styling */
.eq-paren {
  font-family: var(--font-display);
  font-size: var(--text-lg);
  font-weight: 400;
  color: var(--color-text-muted);
  line-height: 1;
}

/* Challenge hint note inside equation */
.eq-note {
  font-size: var(--text-xs);
  color: var(--color-text-faint);
  font-weight: 600;
  margin-left: var(--space-2);
  white-space: nowrap;
}

/* ── Complexity badge ── */
.complexity-badge {
  display: inline-flex;
  align-items: center;
  gap: 3px;
  margin-left: auto;
  padding-left: var(--space-3);
  flex-shrink: 0;
}

.complexity-dot {
  display: inline-block;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--color-border);
  transition: background var(--transition-interactive);
}

.complexity-dot.filled {
  background: var(--color-primary);
}

/* Color shift by fill count — subtler gradient feel */
.complexity-badge .complexity-dot:nth-child(4).filled,
.complexity-badge .complexity-dot:nth-child(5).filled {
  background: #f59e0b;
}

@media print {
  .complexity-badge { display: none !important; }
}

/* ── Work space ── */
.equation-item.with-workspace {
  flex-direction: column;
  align-items: stretch;
  padding-bottom: var(--space-2);
  gap: var(--space-1);
}

.eq-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.work-space {
  margin-left: calc(1.5em + var(--space-2)); /* align with expression */
  margin-top: var(--space-1);
}

.work-lines {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.work-line {
  height: 1px;
  background: var(--color-divider);
  border-radius: 99px;
  width: 100%;
  opacity: 0.7;
}

/* On screen: compact work space */
.work-line {
  height: 18px;
  border-bottom: 1px dashed var(--color-divider);
  background: none;
}

/* ── Animations ── */
@keyframes slideInUp {
  from { opacity: 0; transform: translateY(16px); }
  to { opacity: 1; transform: translateY(0); }
}

.worksheet { animation: slideInUp 0.3s ease; }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

/* ══════════════════════════════════════════════════════════════
   INTERACTIVE MODE
   ══════════════════════════════════════════════════════════════ */

/* Answer input inside equation */
.eq-input {
  display: inline-block;
  width: 72px;
  min-width: 56px;
  padding: 2px 8px;
  border: 2px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-text);
  font-family: var(--font-display);
  font-size: var(--text-lg);
  font-weight: 700;
  text-align: center;
  vertical-align: middle;
  transition: border-color 0.2s, background 0.2s, box-shadow 0.2s;
  -moz-appearance: textfield;
}
/* type=text — no spinners needed */
.eq-input::-webkit-outer-spin-button,
.eq-input::-webkit-inner-spin-button { -webkit-appearance: none; margin: 0; }
.eq-input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px var(--color-primary-light);
}

/* Correct / Wrong states */
.eq-input.input-correct {
  border-color: #10b981;
  background: #ecfdf5;
  color: #065f46;
}
.eq-input.input-wrong {
  border-color: #ef4444;
  background: #fef2f2;
  color: #991b1b;
}
[data-theme='dark'] .eq-input.input-correct { background: #022c22; color: #6ee7b7; }
[data-theme='dark'] .eq-input.input-wrong  { background: #2d0a0a; color: #fca5a5; }

/* Row highlight */
.equation-item.eq-correct { background: #f0fdf4; border-radius: var(--radius-md); }
.equation-item.eq-wrong   { background: #fff5f5; border-radius: var(--radius-md); }
.equation-item.eq-skipped { opacity: 0.55; }
[data-theme='dark'] .equation-item.eq-correct { background: #042a1e; }
[data-theme='dark'] .equation-item.eq-wrong   { background: #2a0a0a; }

/* Feedback icon (✓ / ✗) */
.eq-feedback {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: var(--text-sm);
  font-weight: 700;
  margin-left: 6px;
  vertical-align: middle;
}
.feedback-correct { color: #10b981; }
.feedback-wrong   { color: #ef4444; }
.eq-correct-val {
  font-size: var(--text-xs);
  background: #fee2e2;
  color: #991b1b;
  border-radius: 4px;
  padding: 1px 5px;
}
[data-theme='dark'] .eq-correct-val { background: #3b0a0a; color: #fca5a5; }

/* Work steps textarea */
.work-space--interactive { padding: var(--space-2) 0 0 0; }
.work-textarea {
  width: 100%;
  min-height: 64px;
  padding: var(--space-2) var(--space-3);
  border: 1.5px dashed var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--text-sm);
  resize: vertical;
  transition: border-color 0.2s;
}
.work-textarea:focus {
  outline: none;
  border-color: var(--color-primary);
  border-style: solid;
}

/* Check Answers button (header bar) */
.btn-check {
  background: #10b981 !important;
  color: #fff !important;
  border-color: #10b981 !important;
}
.btn-check:hover { background: #059669 !important; border-color: #059669 !important; }

/* Check bar (below equations) */
.check-bar {
  display: flex;
  justify-content: center;
  padding: var(--space-6) var(--space-4) var(--space-4);
}
.btn-check-inline {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-8);
  background: linear-gradient(135deg, #10b981, #059669);
  color: #fff;
  border: none;
  border-radius: var(--radius-full);
  font-family: var(--font-display);
  font-size: var(--text-base);
  font-weight: 700;
  cursor: pointer;
  box-shadow: 0 4px 16px #10b98144;
  transition: transform 0.15s, box-shadow 0.15s;
}
.btn-check-inline:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 24px #10b98166;
}
.btn-check-inline:active { transform: translateY(0); }

/* Score panel */
.score-panel {
  margin: var(--space-6) 0 var(--space-4);
  border-radius: var(--radius-lg);
  overflow: hidden;
  display: none;
}
.score-panel--visible { display: block; animation: scoreReveal 0.5s cubic-bezier(0.34,1.56,0.64,1) both; }
@keyframes scoreReveal {
  from { opacity: 0; transform: scale(0.85) translateY(20px); }
  to   { opacity: 1; transform: scale(1) translateY(0); }
}

.score-inner {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-8) var(--space-6);
  background: linear-gradient(135deg, var(--color-primary) 0%, #7c3aed 100%);
  color: #fff;
  text-align: center;
}

.score-emoji { font-size: 3rem; line-height: 1; animation: bounce 0.6s 0.3s both; }
@keyframes bounce {
  0%   { transform: scale(0); }
  60%  { transform: scale(1.3); }
  100% { transform: scale(1); }
}

.score-grade {
  font-family: var(--font-display);
  font-size: 3.5rem;
  font-weight: 800;
  line-height: 1;
  letter-spacing: -2px;
}
.grade-Aplus { color: #fde68a; text-shadow: 0 0 20px #fbbf24aa; }
.grade-A     { color: #a7f3d0; }
.grade-B     { color: #bfdbfe; }
.grade-C     { color: #e9d5ff; }
.grade-D     { color: #fecaca; }
.grade-F     { color: #fca5a5; }

.score-numbers {
  font-size: var(--text-xl);
  font-weight: 700;
  opacity: 0.9;
}
.score-pct { font-size: var(--text-sm); opacity: 0.75; margin-left: 4px; }

.score-message {
  font-size: var(--text-base);
  font-weight: 500;
  max-width: 340px;
  opacity: 0.92;
  margin: 0;
}

.score-skipped {
  font-size: var(--text-xs);
  opacity: 0.65;
  margin: 0;
}

.btn-try-again {
  margin-top: var(--space-2);
  padding: var(--space-2) var(--space-6);
  background: rgba(255,255,255,0.2);
  color: #fff;
  border: 2px solid rgba(255,255,255,0.4);
  border-radius: var(--radius-full);
  font-family: var(--font-display);
  font-weight: 700;
  font-size: var(--text-sm);
  cursor: pointer;
  transition: background 0.2s;
}
.btn-try-again:hover { background: rgba(255,255,255,0.35); }

/* Print-only blank line — hidden on screen, shown instead of input when printing */
.print-only { display: none; }

/* Print workspace — always in DOM, hidden on screen */
.print-workspace { display: none; }

@media print {
  /* Hide interactive elements */
  .eq-input         { display: none !important; }
  .work-textarea    { display: none !important; }
  .check-bar,
  .score-panel,
  .eq-feedback      { display: none !important; }
  /* Show the print-only blank answer line */
  .print-only       { display: inline-block !important; }
  /* Show print workspace, hide the screen workspace */
  .print-workspace  { display: block !important; }
  .work-space:not(.print-workspace) { display: none !important; }
}