/* ============================================================
   LLL Algebra — brand styles
   Own visual direction (not copied from lll-chem): a chalkboard/
   chalk-dust theme — equations feel handwritten and worked out,
   not clinical. Balance-beam is the signature motif: algebra IS
   balance, so the equation visually tilts until it's solved.
   Variable *names* match the org's shared/theme.js contract.
   ============================================================ */
:root {
  --bg: #f6f3ee;
  --surface: #ffffff;
  --ink: #1c2027;
  --muted: #6b6459;
  --border: #e3ddd0;
  --accent: #b5461c;       /* chalk-rust — the "active/selected" color */
  --accent-tint: #f4e3d8;
  --correct: #3f7a5c;      /* chalk-green — balanced/correct */
  --correct-tint: #e2efe8;
  --wrong: #b5461c;
  --on-accent: #ffffff;
  --mono: "IBM Plex Mono", ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  --display: "Space Grotesk", -apple-system, "Segoe UI", "Noto Sans JP", sans-serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial,
          "Hiragino Sans", "Noto Sans CJK JP", "Noto Sans KR", "Microsoft YaHei", sans-serif;
  --logo-invert: 0;
}

:root[data-theme="dark"] {
  --bg: #14181d;
  --surface: #1c2128;
  --ink: #eee9df;
  --muted: #8d9199;
  --border: #2b313a;
  --accent: #e2a06b;       /* warm chalk-gold on dark */
  --accent-tint: #35281d;
  --correct: #7fc9a3;
  --correct-tint: #1c2e26;
  --wrong: #e2a06b;
  --on-accent: #14181d;
  --logo-invert: 1;
}

* { box-sizing: border-box; }
html, body { height: 100%; margin: 0; }
body {
  font-family: var(--sans);
  color: var(--ink);
  background: var(--bg);
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Top bar ---------- */
.topbar {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 18px; padding-top: max(14px, env(safe-area-inset-top));
  border-bottom: 1px solid var(--border);
}
.brand { display: flex; align-items: center; gap: 10px; }
.brand-logo img { height: 24px; width: auto; display: block; filter: invert(var(--logo-invert, 0)); }
.brand-name { font-family: var(--display); font-weight: 600; font-size: 17px; letter-spacing: -0.01em; }
.topbar-controls { display: flex; align-items: center; gap: 8px; }

.theme-btn {
  width: 36px; height: 36px; padding: 0;
  display: inline-flex; align-items: center; justify-content: center;
  background: transparent; color: var(--muted);
  border: 1px solid var(--border); border-radius: 10px; cursor: pointer;
}
.theme-btn:hover { color: var(--ink); background: var(--accent-tint); }
.theme-btn .moon { display: none; }
:root[data-theme="dark"] .theme-btn .sun { display: none; }
:root[data-theme="dark"] .theme-btn .moon { display: block; }

.lang-switch {
  display: inline-flex; align-items: center; gap: 6px;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: 10px; padding: 6px 8px 6px 10px;
}
.lang-switch svg { color: var(--muted); flex: none; }
.lang-switch select { border: none; background: transparent; font-family: var(--sans); font-size: 14px; color: var(--ink); cursor: pointer; }

.trophy-btn {
  width: 36px; height: 36px; padding: 0;
  display: inline-flex; align-items: center; justify-content: center;
  background: transparent; font-size: 17px;
  border: 1px solid var(--border); border-radius: 10px; cursor: pointer;
}
.trophy-btn:hover { background: var(--accent-tint); }

/* ---------- How-to-play button ---------- */
.howto-btn {
  width: 36px; height: 36px; padding: 0;
  display: inline-flex; align-items: center; justify-content: center;
  background: transparent; font-size: 16px; color: var(--muted);
  border: 1px solid var(--border); border-radius: 10px; cursor: pointer;
}
.howto-btn:hover { color: var(--ink); background: var(--accent-tint); }

/* ---------- Game stage ---------- */
.stage {
  flex: 1;
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  gap: 28px; padding: 32px 20px; max-width: 640px; margin: 0 auto; width: 100%;
}

.hud { display: flex; gap: 18px; font-family: var(--mono); font-size: 13px; color: var(--muted); }
.hud strong { color: var(--ink); }

/* ---------- Today's Challenge card ---------- */
.daily-card {
  display: flex; align-items: center; gap: 12px;
  width: 100%; max-width: 360px;
  background: var(--surface); border: 1px solid var(--border); border-radius: 14px;
  padding: 14px 18px;
  cursor: pointer; text-align: left;
  transition: border-color .15s ease, background .15s ease;
}
.daily-card:hover { border-color: var(--accent); }
.daily-card.completed {
  background: var(--correct-tint); border-color: var(--correct);
  cursor: default;
}
.daily-card-icon { font-size: 22px; }
.daily-card-title {
  font-family: var(--sans); font-weight: 700; font-size: 14px; color: var(--ink);
}
.daily-card-status {
  font-family: var(--mono); font-size: 12px; color: var(--muted);
  margin-top: 2px;
}
.daily-card.completed .daily-card-status { color: var(--correct); }

/* ---------- Difficulty tier selector ---------- */
.tier-selector { display: flex; gap: 8px; }
.tier-btn {
  font-family: var(--sans); font-size: 13px; font-weight: 600; color: var(--muted);
  background: var(--surface); border: 1px solid var(--border); border-radius: 999px;
  padding: 6px 16px; cursor: pointer;
  transition: border-color .15s ease, color .15s ease, background .15s ease;
}
.tier-btn:hover { color: var(--ink); border-color: var(--accent); }
.tier-btn.active { color: var(--on-accent); background: var(--accent); border-color: var(--accent); }

/* ---------- Streak flash (center-pop) ---------- */
.streak-flash {
  position: fixed;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%) scale(0.7);
  font-family: var(--display); font-size: 22px; font-weight: 700;
  color: var(--accent);
  background: var(--surface); border: 1px solid var(--border); border-radius: 16px;
  padding: 16px 28px;
  opacity: 0;
  pointer-events: none;
  z-index: 500;
  transition: opacity .25s ease, transform .25s ease;
}
.streak-flash.show {
  opacity: 1;
  transform: translate(-50%, -50%) scale(1);
}

/* ---------- Achievement toast (bottom-right, slide up) ---------- */
.achievement-toast {
  position: fixed;
  bottom: 20px; right: 20px;
  display: flex; align-items: center; gap: 10px;
  background: var(--surface); border: 1px solid var(--border); border-radius: 14px;
  padding: 14px 18px;
  font-family: var(--sans); font-size: 14px; font-weight: 600; color: var(--ink);
  box-shadow: 0 8px 24px rgba(0,0,0,0.15);
  transform: translateY(120%);
  opacity: 0;
  z-index: 700;
  transition: transform .35s cubic-bezier(.34,1.56,.64,1), opacity .35s ease;
  pointer-events: none;
}
.achievement-toast.show {
  transform: translateY(0);
  opacity: 1;
}
.achievement-toast-icon { font-size: 20px; }

/* ---------- Achievements modal ---------- */
.achievements-modal {
  position: fixed; inset: 0;
  z-index: 800;
  display: flex; align-items: center; justify-content: center;
  opacity: 0; pointer-events: none;
  transition: opacity .2s ease;
}
.achievements-modal.show { opacity: 1; pointer-events: auto; }
.achievements-modal-backdrop {
  position: absolute; inset: 0;
  background: rgba(0,0,0,0.45);
}
.achievements-modal-card {
  position: relative;
  width: min(420px, 90vw);
  max-height: 80vh;
  overflow-y: auto;
  background: var(--surface); border: 1px solid var(--border); border-radius: 18px;
  padding: 24px;
  transform: scale(0.95);
  transition: transform .2s ease;
}
.achievements-modal.show .achievements-modal-card { transform: scale(1); }
.achievements-modal-header {
  display: flex; align-items: center; justify-content: space-between;
  margin-bottom: 16px;
}
.achievements-modal-header h2 {
  font-family: var(--display); font-size: 18px; margin: 0; color: var(--ink);
}
.achievements-close-btn {
  background: none; border: none; font-size: 18px; color: var(--muted); cursor: pointer;
}
.achievements-list { display: flex; flex-direction: column; gap: 10px; }
.achievement-item {
  display: flex; align-items: center; gap: 12px;
  padding: 12px; border-radius: 12px; border: 1px solid var(--border);
}
.achievement-item.unlocked { background: var(--correct-tint); border-color: var(--correct); }
.achievement-item.locked { opacity: 0.55; }
.achievement-item-icon { font-size: 20px; }
.achievement-item-name { font-family: var(--sans); font-weight: 700; font-size: 14px; color: var(--ink); }
.achievement-item-desc { font-family: var(--sans); font-size: 12px; color: var(--muted); }

/* ---------- Signature: staircase climb ---------- */
.staircase-wrap { width: 100%; max-width: 220px; position: relative; }
.staircase-svg { width: 100%; height: auto; overflow: visible; }
.stair-ground { stroke: var(--border); stroke-width: 2; }
.stair-block { fill: var(--border); }
.stair-summit { font-family: var(--display); font-weight: 700; font-size: 16px; fill: var(--muted); transition: fill .3s ease; }
.stair-summit.solved { fill: var(--correct); }
.stair-marker {
  fill: var(--accent);
  transition: cx .45s cubic-bezier(.34,1.56,.64,1), cy .45s cubic-bezier(.34,1.56,.64,1), fill .3s ease;
}
.stair-marker.solved { fill: var(--correct); }
.stair-marker.shake { animation: stairShake .4s ease; }
@keyframes stairShake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-4px); }
  75% { transform: translateX(4px); }
}

/* ---------- Equation display ---------- */
.equation-card {
  width: 100%;
  background: var(--surface); border: 1px solid var(--border); border-radius: 18px;
  padding: 28px 24px; text-align: center;
}
.equation {
  font-family: var(--mono); font-size: clamp(26px, 6vw, 38px); font-weight: 600;
  letter-spacing: -0.01em; margin: 0;
  transition: opacity .22s ease, transform .22s ease;
}
.equation.updating {
  opacity: 0;
  transform: translateY(6px);
}
.equation .op-highlight { color: var(--accent); }

/* ---------- Operation choice buttons ---------- */
.choices { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; width: 100%; }
.choice-btn {
  font-family: var(--mono); font-size: 15px; font-weight: 600; color: var(--ink);
  background: var(--surface); border: 1.5px solid var(--border); border-radius: 12px;
  padding: 14px 12px; min-height: 52px; cursor: pointer;
  transition: border-color .15s ease, background .15s ease, transform .1s ease;
}
.choice-btn:hover { border-color: var(--accent); }
.choice-btn:active { transform: scale(.97); }
.choice-btn.correct { border-color: var(--correct); background: var(--correct-tint); color: var(--correct); }
.choice-btn.wrong { border-color: var(--wrong); background: var(--accent-tint); color: var(--wrong); }
.choice-btn:disabled { cursor: default; }

/* ---------- Hint / feedback row ---------- */
.controls-row { display: flex; align-items: center; justify-content: space-between; width: 100%; gap: 12px; }
.hint-btn {
  font-family: var(--sans); font-size: 14px; font-weight: 600; color: var(--muted);
  background: transparent; border: 1px dashed var(--border); border-radius: 10px;
  padding: 10px 16px; cursor: pointer;
}
.hint-btn:hover { color: var(--accent); border-color: var(--accent); }
.hint-text { font-size: 14px; color: var(--muted); text-align: center; min-height: 20px; }

.next-btn {
  font-family: var(--sans); font-size: 15px; font-weight: 700; color: var(--on-accent);
  background: var(--accent); border: none; border-radius: 12px;
  padding: 13px 26px; min-height: 48px; cursor: pointer;
  opacity: 0; pointer-events: none; transition: opacity .2s ease;
}
.next-btn.visible { opacity: 1; pointer-events: auto; }

/* ---------- Loading overlay ---------- */
.loading-overlay {
  position: fixed;
  inset: 0;
  z-index: 999;
  background: var(--bg);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: opacity .25s ease;
}
.loading-overlay.hiding {
  opacity: 0;
  pointer-events: none;
}
.loading-dots {
  display: flex;
  gap: 8px;
}
.loading-dots span {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--accent);
  animation: loadingBounce .6s cubic-bezier(.34,1.56,.64,1) infinite alternate;
}
.loading-dots span:nth-child(2) { animation-delay: .15s; }
.loading-dots span:nth-child(3) { animation-delay: .3s; }
@keyframes loadingBounce {
  from { transform: translateY(0); }
  to   { transform: translateY(-18px); }
}

/* ---------- Grand confetti (tier completion) ---------- */
.grand-confetti-layer {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 600;
  overflow: hidden;
}
.grand-confetti-piece {
  position: absolute;
  top: -20px;
  width: 8px;
  height: 14px;
  border-radius: 2px;
  animation-name: grandConfettiFall;
  animation-timing-function: linear;
  animation-fill-mode: forwards;
}
@keyframes grandConfettiFall {
  from { transform: translateY(0) rotate(0deg); opacity: 1; }
  to   { transform: translateY(110vh) rotate(var(--rotate)); opacity: 0.85; }
}

/* ---------- Intro / onboarding (full-screen, animated) ---------- */
.intro-overlay {
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  width: 100vw; height: 100vh;
  z-index: 950;
  display: grid;
  place-items: center;
  background: var(--bg);
  opacity: 0; pointer-events: none;
  transition: opacity .4s ease;
}
.intro-overlay.show { opacity: 1; pointer-events: auto; }
.intro-overlay.hiding { opacity: 0; }

.intro-content {
  width: min(460px, 90vw);
  max-height: 90vh;
  overflow-y: auto;
  padding: 32px 24px;
  text-align: center;
}

.intro-fade {
  opacity: 0;
  transform: translateY(14px);
  transition: opacity .5s ease, transform .5s ease;
  margin-bottom: 18px;
}
.intro-fade.reveal {
  opacity: 1;
  transform: translateY(0);
}
.intro-fade:last-child { margin-bottom: 0; }

.intro-fade .brand-logo img {
  height: 32px; width: auto; display: block; margin: 0 auto 16px;
  filter: invert(var(--logo-invert, 0));
}
.intro-brand-title {
  font-family: var(--display); font-size: 13px; font-weight: 700;
  letter-spacing: 0.08em; text-transform: uppercase;
  color: var(--accent);
  margin: 0 0 4px;
}
.intro-fade h2 {
  font-family: var(--display); font-size: 24px; margin: 0 0 10px; color: var(--ink);
}
.intro-fade p {
  font-family: var(--sans); font-size: 14px; line-height: 1.6; color: var(--muted);
  margin: 0;
}

/* Live demo block inside the intro — one card cycles through 3 states */
.intro-demo-staircase-wrap {
  width: 100%; max-width: 160px;
  margin: 0 auto 16px;
}
.intro-demo-staircase-wrap .staircase-svg { width: 100%; height: auto; overflow: visible; }
.intro-demo-card {
  background: var(--surface); border: 1px solid var(--border); border-radius: 16px;
  padding: 18px;
}
.intro-demo-eq {
  font-size: clamp(22px, 5vw, 28px);
  transition: opacity .22s ease, transform .22s ease;
}
.intro-demo-eq.intro-demo-step-text {
  font-family: var(--sans);
  font-size: 15px;
  font-weight: 600;
  color: var(--accent);
  letter-spacing: normal;
}

.intro-start-btn {
  width: 100%;
  font-family: var(--sans); font-size: 15px; font-weight: 700; color: var(--on-accent);
  background: var(--accent); border: none; border-radius: 12px;
  padding: 14px; cursor: pointer; margin-top: 8px;
}
.intro-start-btn:hover { opacity: 0.9; }

/* ---------- Reduced motion (single consolidated block) ---------- */
@media (prefers-reduced-motion: reduce) {
  .stair-marker, .next-btn { transition: none !important; }
  .stair-marker.shake { animation: none !important; }
  .equation { transition: none !important; }
  .loading-dots span { animation: none !important; }
  .loading-overlay { transition: none !important; }
  .streak-flash { transition: none !important; }
  .grand-confetti-piece { animation: none !important; opacity: 0 !important; }
  .achievement-toast { transition: none !important; }
  .achievements-modal, .achievements-modal-card { transition: none !important; }
  .daily-card { transition: none !important; }
  .intro-overlay, .intro-fade { transition: none !important; }
}