/* =========================================================
   Mathematical Adventure — From Numbers to Algebra
   Stylesheet (mobile-first, accessible, polished game aesthetic)
   ========================================================= */

/* ---------- Design tokens ---------- */
:root {
  /* Palette — adventurous but academic */
  --c-bg: #0f1430;
  --c-bg-grad-1: #1a1f4a;
  --c-bg-grad-2: #0f1430;
  --c-surface: rgba(255, 255, 255, 0.06);
  --c-surface-2: rgba(255, 255, 255, 0.10);
  --c-surface-solid: #1c2150;
  --c-border: rgba(255, 255, 255, 0.12);
  --c-border-strong: rgba(255, 255, 255, 0.24);

  --c-text: #f4f6ff;
  --c-text-dim: #b9c0e0;
  --c-text-mute: #7e87b3;

  --c-primary: #6d4aff;
  --c-primary-2: #8c6bff;
  --c-primary-soft: rgba(109, 74, 255, 0.18);
  --c-accent: #ffce5c;
  --c-accent-2: #ff9d3c;
  --c-success: #4ddc87;
  --c-success-soft: rgba(77, 220, 135, 0.15);
  --c-error: #ff6b8a;
  --c-error-soft: rgba(255, 107, 138, 0.15);
  --c-warning: #ffce5c;
  --c-info: #5cc8ff;

  /* World colors */
  --c-w1: #5cc8ff; /* Integers   */
  --c-w2: #4ddc87; /* Fractions  */
  --c-w3: #ffce5c; /* Patterns   */
  --c-w4: #ff9d3c; /* Variables  */
  --c-w5: #c084fc; /* Expressions*/
  --c-w6: #ff6b8a; /* Equations  */
  --c-w7: #ffd76b; /* Modelling  */

  /* Typography */
  --font-body: "Inter", "Segoe UI", "Helvetica Neue", -apple-system, BlinkMacSystemFont, system-ui, sans-serif;
  --font-head: "Inter", "Segoe UI", -apple-system, system-ui, sans-serif;
  --font-mono: "JetBrains Mono", "Fira Code", Consolas, monospace;

  /* Spacing */
  --sp-1: 4px;
  --sp-2: 8px;
  --sp-3: 12px;
  --sp-4: 16px;
  --sp-5: 24px;
  --sp-6: 32px;
  --sp-7: 48px;
  --sp-8: 64px;

  /* Radius */
  --r-sm: 8px;
  --r-md: 12px;
  --r-lg: 18px;
  --r-xl: 28px;
  --r-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.15);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.25);
  --shadow-lg: 0 18px 48px rgba(0, 0, 0, 0.35);
  --shadow-glow: 0 0 24px rgba(140, 107, 255, 0.45);

  /* Motion */
  --ease-out: cubic-bezier(0.2, 0.8, 0.2, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
  --dur-fast: 140ms;
  --dur: 240ms;
  --dur-slow: 480ms;

  /* Layout */
  --topbar-h: 56px;
  --actionbar-h: 72px;
  --maxw: 760px;
}

/* ---------- Reset / base ---------- */
*, *::before, *::after { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-padding-top: calc(var(--topbar-h) + env(safe-area-inset-top) + var(--sp-3));
}

/* Touch optimisation: kill the tap-highlight flash, the 300 ms click delay
   and accidental double-tap zoom on every interactive control. */
button, a, input, select, textarea, [role="button"], [role="switch"], [role="slider"],
.switch, .mc-option, .ms-option, .match-item, .order-item, .world-node,
.expr-token, .icon-btn, .stat-pill, .modal__close {
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
}

/* Safari still needs the -webkit- prefix for user-select */
.mc-option, .ms-option, .match-item, .order-item, .expr-token, .number-line, .btn {
  -webkit-user-select: none;
}

body {
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.5;
  color: var(--c-text);
  background: radial-gradient(ellipse at top, var(--c-bg-grad-1) 0%, var(--c-bg-grad-2) 70%);
  background-attachment: fixed;
  min-height: 100vh;
  min-height: 100dvh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overscroll-behavior-y: none;
}

h1, h2, h3, h4 { font-family: var(--font-head); font-weight: 700; line-height: 1.2; margin: 0; }
h1 { font-size: 1.5rem; }
h2 { font-size: 1.25rem; }
h3 { font-size: 1.05rem; }
p  { margin: 0 0 var(--sp-3); }
a  { color: var(--c-info); }

button { font-family: inherit; font-size: inherit; cursor: pointer; }
input, button, textarea, select { font: inherit; color: inherit; }

/* Focus ring for accessibility */
:focus-visible {
  outline: 3px solid var(--c-accent);
  outline-offset: 2px;
  border-radius: 4px;
}

.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0);
  white-space: nowrap; border: 0;
}

.skip-link {
  position: absolute;
  top: -100px; left: 0;
  background: var(--c-accent);
  color: #000;
  padding: var(--sp-2) var(--sp-4);
  z-index: 1000;
  border-radius: 0 0 var(--r-md) 0;
}
.skip-link:focus { top: 0; }

/* ---------- App shell ----------
   The app is a full-viewport column: header + scrollable content + footer.
   Header and footer stay pinned to the top/bottom of the viewport; only the
   middle scrolls, so the "Next question" button is always visible. */
.app {
  display: flex;
  flex-direction: column;
  height: 100vh;
  height: 100dvh;
  min-height: 0;
  overflow: hidden;
}

.topbar {
  position: relative;
  z-index: 50;
  flex: 0 0 auto;
  height: calc(var(--topbar-h) + env(safe-area-inset-top));
  padding: env(safe-area-inset-top) calc(var(--sp-3) + env(safe-area-inset-right)) 0 calc(var(--sp-3) + env(safe-area-inset-left));
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-3);
  background: rgba(15, 20, 48, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--c-border);
}
.topbar__left, .topbar__right {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
}
.topbar__title {
  font-weight: 700;
  font-size: 0.95rem;
  letter-spacing: 0.02em;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 38vw;
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  flex: 0 0 auto;
  width: 44px;
  height: 44px;
  border-radius: var(--r-full);
  border: 1px solid var(--c-border);
  background: var(--c-surface);
  color: var(--c-text);
  font-size: 1.1rem;
  transition: background var(--dur-fast) var(--ease-out), transform var(--dur-fast) var(--ease-out);
}
.icon-btn:hover { background: var(--c-surface-2); }
.icon-btn:active { transform: scale(0.92); }

.stat-pill {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 6px 12px;
  min-height: 36px;
  border-radius: var(--r-full);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  font-size: 0.85rem;
  font-weight: 600;
}
.stat-pill__icon { font-size: 0.95rem; }
.stat-pill__value { color: var(--c-text); }
.stat-pill__label { color: var(--c-text-mute); font-size: 0.7rem; }
.stat-pill--streak.active {
  background: var(--c-error-soft);
  border-color: var(--c-error);
  animation: pulse-streak 1.4s var(--ease-out) infinite;
}
@keyframes pulse-streak {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.05); }
}

/* Very small screens: slim down the top bar so the heading still fits */
@media (max-width: 380px) {
  .stat-pill__label { display: none; }
  .stat-pill { padding: 5px 9px; }
  .topbar__right { gap: 6px; }
  .topbar__title { max-width: 26vw; font-size: 0.85rem; }
}

/* Short (e.g. landscape phone) viewports: compact header & footer so more
   content is visible between them */
@media (max-height: 520px) {
  :root { --topbar-h: 48px; --actionbar-h: 56px; }
  .icon-btn { width: 40px; height: 40px; }
  .stat-pill { padding: 4px 10px; min-height: 32px; }
  .btn { min-height: 44px; padding: 10px 16px; }
}

/* ---------- Screen container ---------- */
.screen-container {
  flex: 1 1 auto;
  min-height: 0;
  overflow-y: auto;
  -webkit-overflow-scrolling: touch;
  overscroll-behavior-y: contain;
  width: 100%;
  max-width: var(--maxw);
  margin: 0 auto;
  padding: var(--sp-4) calc(var(--sp-4) + env(safe-area-inset-right)) var(--sp-5) calc(var(--sp-4) + env(safe-area-inset-left));
  display: flex;
  flex-direction: column;
  gap: var(--sp-4);
  outline: none;
  scrollbar-width: thin;
  scrollbar-color: var(--c-border-strong) transparent;
}
.screen-container.no-actionbar {
  padding-bottom: var(--sp-6);
}

/* ---------- Cards / surfaces ---------- */
.card {
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  padding: var(--sp-4);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}
.card--solid {
  background: var(--c-surface-solid);
}
.card--inset {
  background: rgba(0,0,0,0.18);
  border-color: var(--c-border);
}

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-2);
  padding: 12px 20px;
  border-radius: var(--r-md);
  border: 1px solid transparent;
  font-weight: 600;
  font-size: 1rem;
  min-height: 48px;
  transition: transform var(--dur-fast) var(--ease-out), background var(--dur-fast) var(--ease-out), opacity var(--dur-fast);
  -webkit-tap-highlight-color: transparent;
  user-select: none;
}
.btn:active { transform: scale(0.97); }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }
.btn--primary {
  background: linear-gradient(135deg, var(--c-primary) 0%, var(--c-primary-2) 100%);
  color: #fff;
  box-shadow: var(--shadow-glow);
}
.btn--secondary {
  background: var(--c-surface-2);
  color: var(--c-text);
  border-color: var(--c-border-strong);
}
.btn--ghost {
  background: transparent;
  color: var(--c-text);
  border-color: var(--c-border-strong);
}
.btn--success {
  background: linear-gradient(135deg, var(--c-success) 0%, #38c878 100%);
  color: #04231a;
}
.btn--danger {
  background: linear-gradient(135deg, var(--c-error) 0%, #e84871 100%);
  color: #fff;
}
.btn--lg {
  min-height: 56px;
  font-size: 1.1rem;
  padding: 14px 28px;
}
.btn--block { width: 100%; }
.btn--sm {
  min-height: 36px;
  padding: 6px 14px;
  font-size: 0.85rem;
}

/* ---------- Action bar ---------- */
.actionbar {
  position: relative;
  z-index: 40;
  flex: 0 0 auto;
  height: calc(var(--actionbar-h) + env(safe-area-inset-bottom));
  padding: var(--sp-3) calc(var(--sp-4) + env(safe-area-inset-right)) calc(var(--sp-3) + env(safe-area-inset-bottom)) calc(var(--sp-4) + env(safe-area-inset-left));
  background: rgba(15, 20, 48, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-top: 1px solid var(--c-border);
  display: flex;
  gap: var(--sp-3);
  align-items: center;
  justify-content: stretch;
}
.actionbar[hidden] { display: none; }
.actionbar .btn { flex: 1; }
.actionbar #btnHint { flex: 0 0 auto; min-width: 100px; }

/* ---------- Home / menu screen ---------- */
.home-hero {
  text-align: center;
  padding: var(--sp-5) var(--sp-3);
}
.home-hero__title {
  font-size: clamp(1.6rem, 6vw, 2.4rem);
  background: linear-gradient(135deg, var(--c-accent) 0%, var(--c-primary-2) 100%);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  margin-bottom: var(--sp-2);
}
.home-hero__subtitle {
  color: var(--c-text-dim);
  font-size: 0.95rem;
}
.home-hero__badge {
  display: inline-block;
  margin-top: var(--sp-3);
  padding: 6px 14px;
  border-radius: var(--r-full);
  background: var(--c-primary-soft);
  border: 1px solid var(--c-primary);
  color: var(--c-primary-2);
  font-size: 0.8rem;
  font-weight: 600;
}

.home-menu {
  display: flex;
  flex-direction: column;
  gap: var(--sp-3);
  margin: var(--sp-3) 0;
}
.home-menu .btn { width: 100%; }

/* ---------- World map ---------- */
.world-map {
  display: flex;
  flex-direction: column;
  gap: var(--sp-3);
}
.world-node {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  position: relative;
  transition: transform var(--dur) var(--ease-out), border-color var(--dur) var(--ease-out);
  cursor: pointer;
  text-align: left;
  width: 100%;
  color: var(--c-text);
}
.world-node:hover { transform: translateX(4px); }
.world-node:active { transform: scale(0.99); }
.world-node--locked {
  opacity: 0.55;
  cursor: not-allowed;
}
.world-node--locked:hover { transform: none; }
.world-node--mastered {
  border-color: var(--c-success);
  background: linear-gradient(135deg, var(--c-success-soft) 0%, var(--c-surface) 60%);
}
.world-node--in-progress {
  border-color: var(--c-primary);
}

.world-node__icon {
  flex: 0 0 auto;
  width: 56px; height: 56px;
  border-radius: var(--r-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 1.8rem;
  background: var(--c-surface-2);
  border: 1px solid var(--c-border);
}
.world-node__body { flex: 1; min-width: 0; }
.world-node__title {
  font-weight: 700;
  font-size: 1rem;
  margin-bottom: 2px;
}
.world-node__subtitle {
  font-size: 0.8rem;
  color: var(--c-text-dim);
}
.world-node__meta {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
  margin-top: 6px;
}
.world-node__progress {
  flex: 1;
  height: 6px;
  background: rgba(255,255,255,0.08);
  border-radius: var(--r-full);
  overflow: hidden;
}
.world-node__progress > span {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, var(--c-primary) 0%, var(--c-primary-2) 100%);
  border-radius: var(--r-full);
  transition: width var(--dur-slow) var(--ease-out);
}
.world-node__pct {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--c-text-dim);
  min-width: 36px;
  text-align: right;
}
.world-node__status {
  flex: 0 0 auto;
  font-size: 1.2rem;
}

/* World-specific accent colors */
.world-node[data-world="1"] .world-node__icon { background: rgba(92, 200, 255, 0.18); border-color: var(--c-w1); }
.world-node[data-world="2"] .world-node__icon { background: rgba(77, 220, 135, 0.18); border-color: var(--c-w2); }
.world-node[data-world="3"] .world-node__icon { background: rgba(255, 206, 92, 0.18); border-color: var(--c-w3); }
.world-node[data-world="4"] .world-node__icon { background: rgba(255, 157, 60, 0.18); border-color: var(--c-w4); }
.world-node[data-world="5"] .world-node__icon { background: rgba(192, 132, 252, 0.18); border-color: var(--c-w5); }
.world-node[data-world="6"] .world-node__icon { background: rgba(255, 107, 138, 0.18); border-color: var(--c-w6); }
.world-node[data-world="7"] .world-node__icon { background: rgba(255, 215, 107, 0.18); border-color: var(--c-w7); }

/* ---------- Question screen ---------- */
.question-screen {
  display: flex;
  flex-direction: column;
  gap: var(--sp-4);
}

.q-context {
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-left: 4px solid var(--c-primary);
}
.q-context__eyebrow {
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--c-primary-2);
  font-weight: 700;
  margin-bottom: 6px;
}
.q-context__story {
  font-size: 1rem;
  color: var(--c-text);
  line-height: 1.55;
}
.q-context__story .math {
  font-family: var(--font-mono);
  background: rgba(0,0,0,0.25);
  padding: 1px 6px;
  border-radius: 4px;
  font-size: 0.95em;
}

.q-prompt {
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  background: rgba(0,0,0,0.2);
  border: 1px solid var(--c-border);
}
.q-prompt__text {
  font-size: 1.05rem;
  color: var(--c-text);
  line-height: 1.55;
}
.q-prompt__latex {
  margin-top: var(--sp-3);
  padding: var(--sp-4);
  background: var(--c-surface);
  border-radius: var(--r-md);
  text-align: center;
  font-size: 1.4rem;
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
  -webkit-overflow-scrolling: touch;
}
.q-prompt__latex .katex {
  color: var(--c-text);
}

/* ---------- Answer inputs ---------- */
.answer-zone {
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
}
.answer-zone__label {
  display: block;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--c-text-mute);
  margin-bottom: var(--sp-2);
}

.numeric-input,
.text-input {
  width: 100%;
  padding: 14px 16px;
  font-size: 1.25rem;
  font-family: var(--font-mono);
  background: rgba(0,0,0,0.3);
  border: 2px solid var(--c-border-strong);
  border-radius: var(--r-md);
  color: var(--c-text);
  text-align: center;
  transition: border-color var(--dur-fast) var(--ease-out);
}
.numeric-input:focus, .text-input:focus { border-color: var(--c-primary); outline: none; }

.text-input--left { text-align: left; }

/* Multiple choice */
.mc-options {
  display: grid;
  gap: var(--sp-2);
}
.mc-options--2 { grid-template-columns: 1fr; }
@media (min-width: 420px) {
  .mc-options--2 { grid-template-columns: 1fr 1fr; }
}
.mc-option {
  padding: var(--sp-4);
  border-radius: var(--r-md);
  background: var(--c-surface);
  border: 2px solid var(--c-border);
  color: var(--c-text);
  font-size: 1rem;
  text-align: center;
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--dur-fast) var(--ease-out);
  cursor: pointer;
  user-select: none;
}
.mc-option:hover { border-color: var(--c-primary); background: var(--c-surface-2); }
.mc-option:active { transform: scale(0.97); border-color: var(--c-primary); }
.mc-option--selected {
  background: var(--c-primary-soft);
  border-color: var(--c-primary);
}
.mc-option--correct {
  background: var(--c-success-soft);
  border-color: var(--c-success);
}
.mc-option--incorrect {
  background: var(--c-error-soft);
  border-color: var(--c-error);
}

/* Multiple-select */
.ms-options { display: grid; gap: var(--sp-2); }
.ms-option {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-3) var(--sp-4);
  min-height: 56px;
  border-radius: var(--r-md);
  background: var(--c-surface);
  border: 2px solid var(--c-border);
  cursor: pointer;
  user-select: none;
  text-align: left;
  transition: all var(--dur-fast) var(--ease-out);
}
.ms-option:hover { border-color: var(--c-primary); }
.ms-option:active { transform: scale(0.98); }
.ms-option--selected { background: var(--c-primary-soft); border-color: var(--c-primary); }
.ms-option__check {
  flex: 0 0 auto;
  width: 24px; height: 24px;
  border-radius: 6px;
  border: 2px solid var(--c-border-strong);
  background: rgba(0,0,0,0.3);
  display: flex; align-items: center; justify-content: center;
  font-size: 0.9rem;
  color: var(--c-text);
}
.ms-option--selected .ms-option__check {
  background: var(--c-primary);
  border-color: var(--c-primary);
}

/* Ordering / drag list */
.order-list {
  display: flex;
  flex-direction: column;
  gap: var(--sp-2);
}
.order-item {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-3) var(--sp-4);
  min-height: 56px;
  border-radius: var(--r-md);
  background: var(--c-surface);
  border: 2px solid var(--c-border);
  cursor: grab;
  user-select: none;
}
.order-item:active { cursor: grabbing; }
.order-item--dragging { opacity: 0.4; }
.order-item__handle {
  flex: 0 0 auto;
  color: var(--c-text-mute);
  font-size: 1.4rem;
  line-height: 1;
  touch-action: none;
}
.order-item__body { flex: 1; }
.order-item__pos {
  flex: 0 0 auto;
  width: 28px; height: 28px;
  border-radius: var(--r-full);
  background: var(--c-primary-soft);
  color: var(--c-primary-2);
  font-size: 0.8rem;
  font-weight: 700;
  display: flex; align-items: center; justify-content: center;
}

/* Matching */
.match-grid {
  display: grid;
  gap: var(--sp-2);
  grid-template-columns: 1fr 1fr;
}
.match-col {
  display: flex;
  flex-direction: column;
  gap: var(--sp-2);
}
.match-item {
  padding: var(--sp-3);
  border-radius: var(--r-md);
  background: var(--c-surface);
  border: 2px solid var(--c-border);
  text-align: center;
  cursor: pointer;
  user-select: none;
  transition: all var(--dur-fast) var(--ease-out);
  min-height: 56px;
  display: flex;
  align-items: center;
  justify-content: center;
}
.match-item:hover { border-color: var(--c-primary); }
.match-item--selected { background: var(--c-primary-soft); border-color: var(--c-primary); }
.match-item--matched { background: var(--c-success-soft); border-color: var(--c-success); cursor: default; }
.match-item--wrong { animation: shake 0.4s var(--ease-out); background: var(--c-error-soft); border-color: var(--c-error); }

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-6px); }
  75% { transform: translateX(6px); }
}

/* Number line */
.number-line {
  position: relative;
  margin: var(--sp-5) 0 var(--sp-4);
  height: 96px;
  user-select: none;
  touch-action: pan-y;
}
.number-line__track {
  position: absolute;
  top: 50%;
  left: 0; right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--c-error) 0%, var(--c-text-mute) 50%, var(--c-success) 100%);
  border-radius: 2px;
  transform: translateY(-50%);
}
.number-line__tick {
  position: absolute;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 2px;
  height: 16px;
  background: var(--c-border-strong);
}
.number-line__tick-label {
  position: absolute;
  top: calc(50% + 14px);
  transform: translateX(-50%);
  font-size: 0.75rem;
  color: var(--c-text-dim);
  white-space: nowrap;
}
.number-line__marker {
  position: absolute;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 44px;
  height: 44px;
  border-radius: var(--r-full);
  background: var(--c-primary);
  border: 3px solid #fff;
  cursor: grab;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.85rem;
  font-weight: 700;
  color: #fff;
  box-shadow: var(--shadow-md);
  transition: transform var(--dur-fast) var(--ease-out);
  touch-action: none;
}
.number-line__marker:active { cursor: grabbing; transform: translate(-50%, -50%) scale(1.1); }

/* Fraction input */
.fraction-input {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 6px;
  width: 100%;
}
.fraction-input input {
  width: 96px;
  padding: 12px;
  min-height: 48px;
  text-align: center;
  font-size: 1.4rem;
  font-family: var(--font-mono);
  background: rgba(0,0,0,0.3);
  border: 2px solid var(--c-border-strong);
  border-radius: var(--r-sm);
  color: var(--c-text);
}
.fraction-input input:focus { border-color: var(--c-primary); outline: none; }
.fraction-input__bar {
  width: 90px;
  height: 3px;
  background: var(--c-text);
  border-radius: 2px;
}

/* Algebraic input helpers (chips) */
.expr-builder {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-2);
  align-items: center;
  padding: var(--sp-3);
  background: rgba(0,0,0,0.25);
  border-radius: var(--r-md);
  min-height: 60px;
  border: 2px dashed var(--c-border-strong);
}
.expr-builder__chips {
  display: inline-flex;
  flex-wrap: wrap;
  gap: 4px;
}
.expr-chip {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 6px 10px;
  border-radius: var(--r-sm);
  background: var(--c-primary-soft);
  border: 1px solid var(--c-primary);
  color: var(--c-text);
  font-family: var(--font-mono);
  font-size: 0.95rem;
}
.expr-chip__remove {
  background: none;
  border: none;
  color: var(--c-text-dim);
  cursor: pointer;
  font-size: 1rem;
  padding: 0;
  line-height: 1;
}
.expr-chip__remove:hover { color: var(--c-error); }

.expr-tokens {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-2);
  margin-top: var(--sp-2);
}
.expr-token {
  padding: 12px 16px;
  min-height: 44px;
  border-radius: var(--r-sm);
  background: var(--c-surface-2);
  border: 1px solid var(--c-border-strong);
  font-family: var(--font-mono);
  font-size: 1.05rem;
  cursor: pointer;
  user-select: none;
  transition: all var(--dur-fast) var(--ease-out);
}
.expr-token:hover { background: var(--c-primary-soft); border-color: var(--c-primary); }
.expr-token:active { transform: scale(0.95); }

/* ---------- Feedback area ---------- */
.feedback {
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  border: 1px solid;
  font-size: 0.95rem;
  line-height: 1.55;
  animation: feedback-in var(--dur) var(--ease-out);
}
.feedback--correct {
  background: var(--c-success-soft);
  border-color: var(--c-success);
  color: var(--c-success);
}
.feedback--incorrect {
  background: var(--c-error-soft);
  border-color: var(--c-error);
  color: var(--c-error);
}
.feedback--info {
  background: rgba(92, 200, 255, 0.12);
  border-color: var(--c-info);
  color: var(--c-info);
}
.feedback__title {
  font-weight: 700;
  margin-bottom: 6px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.feedback__body {
  color: var(--c-text);
}

/* Feedback recap: repeats the question and the correct answer */
.feedback__recap {
  margin: var(--sp-3) 0;
  padding: var(--sp-3);
  border-radius: var(--r-md);
  background: rgba(0, 0, 0, 0.25);
  border: 1px solid var(--c-border);
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.feedback__line {
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 6px;
}
.feedback__line--math {
  justify-content: center;
  padding: var(--sp-2);
  background: rgba(0, 0, 0, 0.2);
  border-radius: var(--r-sm);
  font-size: 1.15rem;
}
.feedback__line-label {
  flex: 0 0 auto;
  font-weight: 700;
  color: var(--c-text-dim);
}
.feedback__line-value {
  color: var(--c-text);
  overflow-wrap: anywhere;
}
.feedback__line-value .katex { color: var(--c-text); }
.feedback__line--answer .feedback__line-value {
  font-weight: 700;
  color: var(--c-success);
}
.feedback--incorrect .feedback__line--answer .feedback__line-value {
  color: var(--c-error);
}
.feedback__line--yours .feedback__line-value {
  opacity: 0.8;
}

.feedback__math {
  margin-top: var(--sp-2);
  padding: var(--sp-3);
  background: rgba(0,0,0,0.25);
  border-radius: var(--r-md);
  text-align: center;
}

@keyframes feedback-in {
  from { opacity: 0; transform: translateY(8px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* Hint box */
.hint-box {
  padding: var(--sp-3) var(--sp-4);
  border-radius: var(--r-md);
  background: rgba(255, 206, 92, 0.1);
  border: 1px solid var(--c-warning);
  color: var(--c-text);
  font-size: 0.9rem;
  animation: feedback-in var(--dur) var(--ease-out);
}
.hint-box__label {
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--c-warning);
  font-weight: 700;
  margin-bottom: 4px;
}

/* ---------- Progress bar ---------- */
.progress-bar {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
}
.progress-bar__track {
  flex: 1;
  height: 8px;
  background: rgba(255,255,255,0.08);
  border-radius: var(--r-full);
  overflow: hidden;
}
.progress-bar__fill {
  height: 100%;
  background: linear-gradient(90deg, var(--c-primary) 0%, var(--c-primary-2) 100%);
  border-radius: var(--r-full);
  transition: width var(--dur-slow) var(--ease-out);
}
.progress-bar__label {
  font-size: 0.75rem;
  color: var(--c-text-dim);
  font-weight: 600;
  min-width: 60px;
  text-align: right;
}

/* ---------- World header ---------- */
.world-header {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-3) var(--sp-4);
  border-radius: var(--r-lg);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
}
.world-header__icon {
  flex: 0 0 auto;
  width: 48px; height: 48px;
  border-radius: var(--r-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 1.6rem;
  background: var(--c-surface-2);
}
.world-header__title {
  font-weight: 700;
  font-size: 1rem;
}
.world-header__subtitle {
  font-size: 0.75rem;
  color: var(--c-text-dim);
}

/* ---------- Toasts ---------- */
.toast-area {
  position: fixed;
  top: calc(var(--topbar-h) + env(safe-area-inset-top) + var(--sp-2));
  left: 50%;
  transform: translateX(-50%);
  z-index: 100;
  display: flex;
  flex-direction: column;
  gap: var(--sp-2);
  width: calc(100% - var(--sp-4));
  max-width: 480px;
  pointer-events: none;
}
.toast {
  padding: var(--sp-3) var(--sp-4);
  border-radius: var(--r-md);
  background: var(--c-surface-solid);
  border: 1px solid var(--c-border-strong);
  color: var(--c-text);
  font-size: 0.9rem;
  font-weight: 600;
  box-shadow: var(--shadow-md);
  animation: toast-in var(--dur) var(--ease-spring);
  pointer-events: auto;
}
.toast--success { border-color: var(--c-success); color: var(--c-success); }
.toast--error { border-color: var(--c-error); color: var(--c-error); }
.toast--info { border-color: var(--c-info); color: var(--c-info); }
.toast--achievement {
  background: linear-gradient(135deg, var(--c-primary) 0%, var(--c-primary-2) 100%);
  color: #fff;
  border-color: transparent;
  box-shadow: var(--shadow-glow);
  display: flex;
  align-items: center;
  gap: var(--sp-3);
}
.toast--achievement .toast__icon { font-size: 1.5rem; }
.toast--achievement .toast__title { font-weight: 700; }
.toast--achievement .toast__body { font-size: 0.8rem; opacity: 0.9; }

@keyframes toast-in {
  from { opacity: 0; transform: translateY(-12px) scale(0.95); }
  to   { opacity: 1; transform: translateY(0) scale(1); }
}

/* ---------- Modal ---------- */
.modal-root { position: fixed; inset: 0; z-index: 200; pointer-events: none; }
.modal-backdrop {
  position: absolute;
  inset: 0;
  background: rgba(0, 0, 0, 0.7);
  -webkit-backdrop-filter: blur(4px);
  backdrop-filter: blur(4px);
  animation: feedback-in var(--dur) var(--ease-out);
  pointer-events: auto;
}
.modal {
  position: absolute;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  width: calc(100% - var(--sp-5));
  max-width: 540px;
  max-height: calc(100vh - var(--sp-6));
  overflow-y: auto;
  background: var(--c-surface-solid);
  border: 1px solid var(--c-border-strong);
  border-radius: var(--r-xl);
  padding: var(--sp-5);
  box-shadow: var(--shadow-lg);
  animation: modal-in var(--dur) var(--ease-spring);
  pointer-events: auto;
}
@keyframes modal-in {
  from { opacity: 0; transform: translate(-50%, -45%) scale(0.95); }
  to   { opacity: 1; transform: translate(-50%, -50%) scale(1); }
}
.modal__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--sp-4);
}
.modal__title { font-size: 1.2rem; }
.modal__close {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: none;
  border: none;
  font-size: 1.6rem;
  color: var(--c-text-dim);
  cursor: pointer;
  line-height: 1;
}
.modal__close:hover { background: var(--c-surface-2); color: var(--c-text); }
.modal__body { font-size: 0.95rem; line-height: 1.55; }
.modal__footer {
  margin-top: var(--sp-4);
  display: flex;
  gap: var(--sp-2);
  justify-content: flex-end;
}

/* ---------- Dashboard ---------- */
.dashboard {
  display: flex;
  flex-direction: column;
  gap: var(--sp-4);
}
.dashboard-section {
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
}
.dashboard-section__title {
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--c-text-mute);
  font-weight: 700;
  margin-bottom: var(--sp-3);
}

.mastery-map {
  display: flex;
  flex-direction: column;
  gap: var(--sp-2);
}
.mastery-row {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-2) var(--sp-3);
  border-radius: var(--r-md);
  background: rgba(0,0,0,0.18);
}
.mastery-row__icon { flex: 0 0 auto; font-size: 1.1rem; }
.mastery-row__name { flex: 0 0 auto; width: 110px; font-size: 0.85rem; font-weight: 600; }
.mastery-row__bar {
  flex: 1;
  height: 8px;
  background: rgba(255,255,255,0.08);
  border-radius: var(--r-full);
  overflow: hidden;
}
.mastery-row__bar > span {
  display: block;
  height: 100%;
  border-radius: var(--r-full);
  transition: width var(--dur-slow) var(--ease-out);
}
.mastery-row__pct {
  flex: 0 0 auto;
  width: 44px;
  font-size: 0.8rem;
  font-weight: 700;
  text-align: right;
  color: var(--c-text-dim);
}
.mastery-row--mastered .mastery-row__bar > span { background: var(--c-success); }
.mastery-row--developing .mastery-row__bar > span { background: linear-gradient(90deg, var(--c-warning), var(--c-primary-2)); }
.mastery-row--locked .mastery-row__bar > span { background: var(--c-text-mute); }
.mastery-row--locked .mastery-row__name,
.mastery-row--locked .mastery-row__pct { color: var(--c-text-mute); }

.achievement-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(110px, 1fr));
  gap: var(--sp-2);
}
.achievement {
  padding: var(--sp-3);
  border-radius: var(--r-md);
  background: rgba(0,0,0,0.18);
  border: 1px solid var(--c-border);
  text-align: center;
  font-size: 0.7rem;
  transition: all var(--dur) var(--ease-out);
}
.achievement--unlocked {
  background: linear-gradient(135deg, var(--c-primary-soft) 0%, var(--c-surface) 100%);
  border-color: var(--c-primary);
}
.achievement--locked { opacity: 0.4; }
.achievement__icon { font-size: 1.6rem; display: block; margin-bottom: 4px; }
.achievement__name { font-weight: 700; font-size: 0.75rem; color: var(--c-text); }
.achievement__desc { color: var(--c-text-dim); font-size: 0.65rem; margin-top: 2px; }

/* ---------- Debug mode ---------- */
.debug-panel {
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  background: rgba(0,0,0,0.5);
  border: 1px dashed var(--c-warning);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--c-warning);
  overflow-x: auto;
  white-space: pre;
  margin-top: var(--sp-3);
  -webkit-overflow-scrolling: touch;
}
.debug-row {
  display: flex;
  justify-content: space-between;
  gap: var(--sp-3);
  padding: 4px 0;
  border-bottom: 1px dotted rgba(255,206,92,0.15);
}
.debug-row__key { color: var(--c-text-mute); }
.debug-row__val { color: var(--c-text); text-align: right; }

/* ---------- Settings ---------- */
.settings-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-3);
  padding: var(--sp-3) 0;
  border-bottom: 1px solid var(--c-border);
}
.settings-row:last-child { border-bottom: none; }
.settings-row__label { font-weight: 600; font-size: 0.95rem; }
.settings-row__hint { font-size: 0.75rem; color: var(--c-text-dim); margin-top: 2px; }
.settings-row__control { flex: 0 0 auto; }

.switch {
  position: relative;
  width: 52px; height: 30px;
  background: var(--c-surface-2);
  border-radius: var(--r-full);
  cursor: pointer;
  border: 1px solid var(--c-border-strong);
  transition: background var(--dur-fast) var(--ease-out);
  flex: 0 0 auto;
}
.switch--on { background: var(--c-primary); border-color: var(--c-primary); }
.switch::after {
  content: "";
  position: absolute;
  top: 2px; left: 2px;
  width: 24px; height: 24px;
  background: #fff;
  border-radius: var(--r-full);
  transition: transform var(--dur-fast) var(--ease-out);
}
.switch--on::after { transform: translateX(24px); }

/* ---------- Misc / utilities ---------- */
.row { display: flex; gap: var(--sp-2); align-items: center; }
.row--wrap { flex-wrap: wrap; }
.row--between { justify-content: space-between; }
.row--center { justify-content: center; }
.col { display: flex; flex-direction: column; gap: var(--sp-2); }
.gap-sm { gap: var(--sp-2); }
.gap-md { gap: var(--sp-3); }
.gap-lg { gap: var(--sp-4); }
.mt-sm { margin-top: var(--sp-2); }
.mt-md { margin-top: var(--sp-4); }
.mt-lg { margin-top: var(--sp-6); }
.text-dim { color: var(--c-text-dim); }
.text-mute { color: var(--c-text-mute); }
.text-center { text-align: center; }
.text-mono { font-family: var(--font-mono); }
.hidden { display: none !important; }
.tag {
  display: inline-block;
  padding: 2px 8px;
  border-radius: var(--r-full);
  background: var(--c-primary-soft);
  border: 1px solid var(--c-primary);
  color: var(--c-primary-2);
  font-size: 0.7rem;
  font-weight: 600;
}
.tag--success { background: var(--c-success-soft); border-color: var(--c-success); color: var(--c-success); }
.tag--warning { background: rgba(255,206,92,0.12); border-color: var(--c-warning); color: var(--c-warning); }
.tag--error { background: var(--c-error-soft); border-color: var(--c-error); color: var(--c-error); }
.tag--info { background: rgba(92,200,255,0.12); border-color: var(--c-info); color: var(--c-info); }

/* ---------- Animations ---------- */
@keyframes pop {
  0%   { transform: scale(0.6); opacity: 0; }
  60%  { transform: scale(1.1); opacity: 1; }
  100% { transform: scale(1); }
}
.animate-pop { animation: pop var(--dur) var(--ease-spring); }

@keyframes float-up {
  0%   { transform: translateY(0) scale(1); opacity: 1; }
  100% { transform: translateY(-60px) scale(1.2); opacity: 0; }
}
.float-up {
  position: absolute;
  pointer-events: none;
  font-weight: 700;
  font-size: 1.2rem;
  color: var(--c-accent);
  animation: float-up 1s var(--ease-out) forwards;
  z-index: 90;
}

@keyframes confetti-fall {
  0% { transform: translateY(-100vh) rotate(0deg); opacity: 1; }
  100% { transform: translateY(100vh) rotate(720deg); opacity: 0; }
}
.confetti {
  position: fixed;
  top: 0;
  width: 8px; height: 14px;
  pointer-events: none;
  z-index: 150;
  animation: confetti-fall 2.4s linear forwards;
}

@keyframes flash-correct {
  0%   { background: var(--c-success-soft); }
  100% { background: transparent; }
}
.flash-correct { animation: flash-correct 0.6s var(--ease-out); }

/* ---------- Reduced motion ---------- */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
  .stat-pill--streak.active { animation: none; }
}

/* ---------- Larger screens ---------- */
@media (min-width: 768px) {
  body { font-size: 17px; }
  .screen-container { padding: var(--sp-6) var(--sp-4) var(--sp-7); }
  .home-hero { padding: var(--sp-7) var(--sp-3); }
  .home-hero__title { font-size: 2.4rem; }
  .world-node { padding: var(--sp-5); }
  .world-node__icon { width: 64px; height: 64px; font-size: 2rem; }
  .achievement-grid { grid-template-columns: repeat(auto-fill, minmax(140px, 1fr)); }
}

/* Tablet adjustments */
@media (min-width: 600px) and (max-width: 768px) {
  .mc-options--2 { grid-template-columns: 1fr 1fr; }
}

/* Extra-large screens: a little more breathing room */
@media (min-width: 1024px) {
  .screen-container { padding-top: var(--sp-7); }
  .home-hero__title { font-size: 2.6rem; }
}

/* KaTeX overrides */
.katex { font-size: 1.1em; }
.katex-display { margin: 0; }
.q-prompt__latex .katex-display { margin: 0; }