:root {
  --bg: #090b12;
  --panel: rgba(18, 22, 33, 0.88);
  --panel-strong: #151927;
  --line: rgba(255, 255, 255, 0.1);
  --text: #f7f8fc;
  --muted: #aeb6c7;
  --cyan: #56d6ff;
  --gold: #f6c75e;
  --green: #69e6a5;
  --pink: #ff6f9f;
  --red: #ff7878;
  --shadow: 0 24px 70px rgba(0, 0, 0, 0.36);
  --radius: 8px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  color: var(--text);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background:
    radial-gradient(circle at 18% 8%, rgba(86, 214, 255, 0.16), transparent 26rem),
    radial-gradient(circle at 86% 22%, rgba(255, 111, 159, 0.12), transparent 22rem),
    linear-gradient(135deg, #080a10 0%, #11131d 46%, #090b12 100%);
  overflow-x: hidden;
}

#starfield {
  position: fixed;
  inset: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
  opacity: 0.55;
}

button {
  border: 0;
  color: inherit;
  font: inherit;
  cursor: pointer;
}

.app-shell {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: 300px minmax(0, 1fr);
  min-height: 100vh;
}

.sidebar {
  padding: 24px;
  border-right: 1px solid var(--line);
  background: rgba(9, 11, 18, 0.78);
  backdrop-filter: blur(18px);
}

.brand, .player-card, .topbar, .lesson-hero, .mode-panel, .topic-card, .achievement-card, .quiz-panel {
  border: 1px solid var(--line);
  background: var(--panel);
  box-shadow: var(--shadow);
  border-radius: var(--radius);
}

.brand {
  display: flex;
  gap: 14px;
  align-items: center;
  padding: 14px;
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 48px;
  height: 48px;
  border-radius: 8px;
  background: linear-gradient(135deg, var(--cyan), var(--pink));
  color: #080a10;
  font-weight: 900;
}

.brand h1, .brand p, .player-card h2, .player-card p { margin: 0; }
.brand h1 { font-size: 1.05rem; }
.brand p, .player-card p, .muted { color: var(--muted); }

.nav-tabs {
  display: grid;
  gap: 10px;
  margin: 24px 0;
}

.nav-tab, .ghost-button, .primary-button, .choice-button {
  border-radius: 8px;
  transition: transform 150ms ease, background 150ms ease, border-color 150ms ease;
}

.nav-tab {
  padding: 13px 14px;
  text-align: left;
  background: rgba(255, 255, 255, 0.045);
  border: 1px solid transparent;
}

.nav-tab:hover, .nav-tab.active {
  transform: translateY(-1px);
  border-color: rgba(86, 214, 255, 0.45);
  background: rgba(86, 214, 255, 0.12);
}

.player-card {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 14px;
}

.level-ring {
  width: 58px;
  height: 58px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  color: #08100c;
  font-weight: 900;
  background: conic-gradient(var(--green), var(--cyan), var(--gold), var(--green));
}

.sidebar-progress { margin-top: 20px; color: var(--muted); }
.sidebar-progress strong { display: block; margin-top: 8px; color: var(--text); }

.progress-track {
  height: 10px;
  overflow: hidden;
  margin-top: 10px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.08);
}

.progress-fill {
  height: 100%;
  width: 0%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--green), var(--cyan), var(--gold));
  transition: width 300ms ease;
}

.main-stage {
  min-width: 0;
  padding: 24px;
}

.topbar {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  align-items: center;
  padding: 18px;
  margin-bottom: 20px;
}

.eyebrow {
  margin: 0 0 4px;
  color: var(--gold);
  text-transform: uppercase;
  letter-spacing: 0;
  font-size: 0.78rem;
  font-weight: 800;
}

.topbar h2 { margin: 0; font-size: clamp(1.5rem, 2.4vw, 2.5rem); }
.topbar-actions { display: flex; gap: 10px; flex-wrap: wrap; }

.ghost-button, .primary-button {
  padding: 11px 14px;
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.06);
}

.ghost-button:hover, .primary-button:hover { transform: translateY(-1px); background: rgba(255, 255, 255, 0.1); }
.ghost-button.danger { color: var(--red); }
.primary-button { background: linear-gradient(135deg, rgba(86, 214, 255, 0.28), rgba(105, 230, 165, 0.24)); }

.view { display: none; animation: fadeIn 240ms ease; }
.view.active { display: block; }

.stats-grid, .topic-grid, .achievement-grid, .mode-grid {
  display: grid;
  gap: 14px;
}

.stats-grid {
  grid-template-columns: repeat(4, minmax(0, 1fr));
  margin-bottom: 18px;
}

.stat-card {
  padding: 16px;
  border-radius: var(--radius);
  background: rgba(255, 255, 255, 0.065);
  border: 1px solid var(--line);
}

.stat-card span { display: block; color: var(--muted); font-size: 0.85rem; }
.stat-card strong { display: block; margin-top: 6px; font-size: 1.5rem; }

.topic-grid { grid-template-columns: repeat(auto-fill, minmax(245px, 1fr)); }

.topic-card {
  min-height: 210px;
  padding: 16px;
  display: flex;
  flex-direction: column;
  gap: 10px;
  position: relative;
  overflow: hidden;
}

.topic-card::after {
  content: "";
  position: absolute;
  inset: auto 14px 14px auto;
  width: 64px;
  height: 64px;
  border-radius: 50%;
  background: var(--accent, var(--cyan));
  opacity: 0.12;
}

.topic-card h3 { margin: 0; font-size: 1.05rem; }
.topic-card p { margin: 0; color: var(--muted); line-height: 1.45; }
.topic-card .domain { color: var(--gold); font-size: 0.78rem; font-weight: 800; }

.pill-row { display: flex; flex-wrap: wrap; gap: 7px; margin-top: auto; }
.pill {
  padding: 5px 8px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.08);
  color: var(--muted);
  font-size: 0.78rem;
}

.lesson-hero {
  overflow: hidden;
}

.lesson-banner {
  min-height: 220px;
  padding: 24px;
  display: grid;
  align-content: end;
  background:
    linear-gradient(135deg, rgba(9, 11, 18, 0.14), rgba(9, 11, 18, 0.9)),
    var(--scene);
}

.lesson-banner h3 {
  max-width: 760px;
  margin: 8px 0 0;
  font-size: clamp(1.8rem, 4vw, 4rem);
}

.lesson-body {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 340px;
  gap: 18px;
  padding: 18px;
}

.story-panel, .checkpoint-panel {
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(255, 255, 255, 0.05);
}

.story-panel h4, .checkpoint-panel h4, .quiz-panel h4 { margin: 0 0 8px; }
.story-panel p, .checkpoint-panel p { color: var(--muted); line-height: 1.65; }

.stepper {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 14px;
}

.step-dot {
  min-width: 38px;
  height: 34px;
  border-radius: 8px;
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.06);
}

.step-dot.active { background: rgba(86, 214, 255, 0.24); border-color: var(--cyan); }

.quiz-panel {
  padding: 18px;
  margin-top: 18px;
}

.choice-list {
  display: grid;
  gap: 10px;
  margin-top: 12px;
}

.choice-button {
  padding: 13px;
  text-align: left;
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.055);
}

.choice-button:hover { border-color: rgba(86, 214, 255, 0.55); }
.choice-button.correct { background: rgba(105, 230, 165, 0.18); border-color: var(--green); }
.choice-button.wrong { background: rgba(255, 120, 120, 0.16); border-color: var(--red); }

.feedback {
  min-height: 46px;
  margin-top: 12px;
  color: var(--muted);
  line-height: 1.5;
}

.mode-grid { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.mode-panel { padding: 18px; }
.mode-panel h3 { margin-top: 0; }

.achievement-grid { grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); }
.achievement-card {
  padding: 16px;
  opacity: 0.55;
}
.achievement-card.unlocked { opacity: 1; border-color: rgba(246, 199, 94, 0.5); }
.achievement-icon { font-size: 2rem; }

.toast {
  position: fixed;
  right: 22px;
  bottom: 22px;
  max-width: min(380px, calc(100vw - 44px));
  transform: translateY(120%);
  padding: 14px 16px;
  border: 1px solid rgba(246, 199, 94, 0.45);
  border-radius: var(--radius);
  background: rgba(18, 22, 33, 0.96);
  box-shadow: var(--shadow);
  transition: transform 250ms ease;
  z-index: 5;
}
.toast.show { transform: translateY(0); }

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

@media (max-width: 920px) {
  .app-shell { grid-template-columns: 1fr; }
  .sidebar { position: static; border-right: 0; border-bottom: 1px solid var(--line); }
  .nav-tabs { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .lesson-body { grid-template-columns: 1fr; }
  .stats-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 560px) {
  .main-stage, .sidebar { padding: 14px; }
  .topbar { align-items: stretch; flex-direction: column; }
  .topbar-actions { width: 100%; }
  .topbar-actions button { flex: 1; }
  .nav-tabs { grid-template-columns: 1fr; }
  .stats-grid { grid-template-columns: 1fr; }
}