:root {
  --ink: #1f2937;
  --bg: #fdf6ec;
  --card: #ffffff;
  --shadow: 0 4px 12px rgba(31, 41, 55, 0.12);
  --radius: 18px;
  --nav-bg: #1f2937;
}

body.space { --accent: #7c3aed; --accent-soft: #ede9fe; }
body.animals { --accent: #059669; --accent-soft: #d1fae5; }
body.body { --accent: #e11d48; --accent-soft: #ffe4e6; }
body.ocean { --accent: #0284c7; --accent-soft: #e0f2fe; }
body.weather { --accent: #f59e0b; --accent-soft: #fef3c7; }
body.science { --accent: #d946ef; --accent-soft: #fae8ff; }
body.dinosaurs { --accent: #a16207; --accent-soft: #fefce8; }
body.earth { --accent: #4d7c0f; --accent-soft: #ecfccb; }
body.food { --accent: #ea580c; --accent-soft: #ffedd5; }
body.technology { --accent: #475569; --accent-soft: #f1f5f9; }
body.sound { --accent: #4338ca; --accent-soft: #e0e7ff; }
body.light { --accent: #ca8a04; --accent-soft: #fef9c3; }
body.birds { --accent: #0f766e; --accent-soft: #ccfbf1; }
body.math { --accent: #0891b2; --accent-soft: #cffafe; }

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  color: var(--ink);
  background: var(--bg);
  font-size: 19px;
  line-height: 1.55;
}

img {
  max-width: 100%;
}

.site-header {
  background: var(--nav-bg);
  color: #fff;
  position: sticky;
  top: 0;
  z-index: 10;
}

.nav-wrap {
  max-width: 1000px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 12px 18px;
}

.logo {
  color: #fff;
  font-size: 22px;
  font-weight: 800;
  text-decoration: none;
  letter-spacing: 0.3px;
}

.nav-toggle {
  display: none;
  background: none;
  border: 2px solid rgba(255, 255, 255, 0.6);
  color: #fff;
  font-size: 20px;
  padding: 4px 12px;
  border-radius: 10px;
  cursor: pointer;
}

.nav-links {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-links a {
  display: inline-block;
  color: #e5e7eb;
  text-decoration: none;
  padding: 8px 12px;
  border-radius: 999px;
  font-weight: 600;
  font-size: 16px;
  transition: background 0.2s, color 0.2s;
}

.nav-links a:hover {
  background: rgba(255, 255, 255, 0.12);
}

.nav-links a.active {
  background: var(--accent, #6366f1);
  color: #fff;
}

main {
  max-width: 1000px;
  margin: 0 auto;
  padding: 24px 18px 48px;
}

.hero {
  text-align: center;
  padding: 28px 0 12px;
}

.hero h1 {
  font-size: clamp(32px, 6vw, 52px);
  margin: 10px 0 6px;
  color: var(--ink);
}

.hero .subtitle {
  font-size: 20px;
  max-width: 640px;
  margin: 0 auto 8px;
  color: #4b5563;
}

.hero .big-emoji {
  font-size: 64px;
  line-height: 1.2;
}

.hero-badge {
  display: inline-block;
  margin-top: 12px;
  padding: 8px 16px;
  border-radius: 999px;
  font-weight: 700;
  color: #fff;
  font-size: 16px;
}

section {
  margin-bottom: 34px;
}

.fact-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}

.fact-card {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 20px;
  display: flex;
  gap: 14px;
  align-items: flex-start;
  border-top: 6px solid var(--accent);
}

.fact-emoji {
  font-size: 40px;
  line-height: 1;
  flex-shrink: 0;
}

.fact-text strong {
  color: var(--accent);
}

.didyouknow {
  background: var(--accent-soft);
  border-radius: var(--radius);
  padding: 20px 24px;
  border-left: 8px solid var(--accent);
  font-size: 21px;
}

.didyouknow .didyouknow-label {
  display: block;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 1px;
  font-size: 15px;
  color: var(--accent);
  margin-bottom: 6px;
}

.topic-tiles {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 18px;
}

.tile {
  display: block;
  text-decoration: none;
  color: var(--ink);
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 24px 20px;
  text-align: center;
  transition: transform 0.15s, box-shadow 0.15s;
}

.tile:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 20px rgba(31, 41, 55, 0.18);
}

.tile .tile-emoji {
  font-size: 52px;
  display: block;
  margin-bottom: 8px;
}

.tile .tile-title {
  font-size: 22px;
  font-weight: 800;
  display: block;
}

.tile .tile-count {
  display: inline-block;
  margin-top: 10px;
  padding: 4px 12px;
  border-radius: 999px;
  font-size: 14px;
  font-weight: 700;
  background: var(--accent-soft);
  color: var(--accent);
}

.big-tile {
  background: var(--ink);
  color: #fff;
}

.big-tile .tile-title {
  color: #fff;
}

.big-tile .tile-count {
  background: rgba(255, 255, 255, 0.18);
  color: #fff;
}

.page-links {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 20px;
}

.btn {
  display: inline-block;
  text-decoration: none;
  padding: 12px 22px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 17px;
  background: var(--accent, #6366f1);
  color: #fff;
  border: none;
  cursor: pointer;
  transition: filter 0.15s;
}

.btn:hover {
  filter: brightness(1.08);
}

.btn.btn-ghost {
  background: var(--accent-soft);
  color: var(--ink);
}

h2.section-title {
  font-size: 28px;
  margin: 30px 0 14px;
}

h2.section-title .emoji {
  margin-right: 6px;
}

/* Quiz */
.quiz-box {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 26px;
  max-width: 680px;
  margin: 0 auto;
  text-align: center;
}

.progress-text {
  font-weight: 700;
  color: #6b7280;
  margin-bottom: 8px;
}

.progress-bar {
  height: 14px;
  background: #e5e7eb;
  border-radius: 999px;
  overflow: hidden;
  margin-bottom: 24px;
}

.progress-fill {
  height: 100%;
  background: var(--accent, #6366f1);
  border-radius: 999px;
  transition: width 0.3s;
}

.quiz-question {
  font-size: 24px;
  font-weight: 800;
  margin: 0 0 20px;
}

.quiz-options {
  display: grid;
  gap: 12px;
  margin-bottom: 18px;
}

.quiz-option {
  display: block;
  width: 100%;
  text-align: left;
  padding: 14px 18px;
  border-radius: 14px;
  border: 3px solid #e5e7eb;
  background: #fff;
  font-size: 18px;
  font-weight: 600;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s;
}

.quiz-option:hover:not(:disabled) {
  border-color: var(--accent, #6366f1);
}

.quiz-option.correct {
  border-color: #16a34a;
  background: #f0fdf4;
}

.quiz-option.wrong {
  border-color: #dc2626;
  background: #fef2f2;
}

.quiz-option:disabled {
  cursor: default;
}

.quiz-feedback {
  font-size: 18px;
  font-weight: 700;
  min-height: 28px;
  margin-bottom: 10px;
}

.quiz-feedback.ok {
  color: #16a34a;
}

.quiz-feedback.no {
  color: #dc2626;
}

.result-title {
  font-size: 40px;
  margin: 0 0 8px;
}

.result-stars {
  font-size: 40px;
  letter-spacing: 4px;
  margin: 6px 0;
}

.result-msg {
  font-size: 20px;
  font-weight: 700;
  margin: 0 0 6px;
}

.result-score {
  color: #6b7280;
  margin: 0 0 20px;
}

.hidden {
  display: none !important;
}

/* Experiments */
.exp-card {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 22px 24px;
  margin-bottom: 18px;
  border-top: 6px solid var(--accent);
}

.exp-card h3 {
  margin: 0 0 4px;
  font-size: 24px;
}

.exp-card .exp-emoji {
  font-size: 30px;
}

.tag-grownup {
  display: inline-block;
  background: #fee2e2;
  color: #b91c1c;
  font-weight: 800;
  padding: 6px 14px;
  border-radius: 999px;
  font-size: 15px;
  margin-bottom: 10px;
}

.exp-card ul,
.exp-card ol {
  margin: 8px 0;
  padding-left: 24px;
}

.exp-card h4 {
  margin: 14px 0 4px;
  font-size: 18px;
  color: var(--accent);
}

.what-happens {
  background: var(--accent-soft);
  border-radius: 12px;
  padding: 12px 16px;
  margin-top: 12px;
}

/* Footer */
.site-footer {
  background: var(--nav-bg);
  color: #cbd5e1;
  text-align: center;
  padding: 22px 18px;
  font-size: 15px;
}

.site-footer p {
  margin: 4px 0;
}

@media (max-width: 640px) {
  .nav-toggle {
    display: inline-block;
  }

  .nav-links {
    display: none;
    flex-direction: column;
    width: 100%;
    background: var(--nav-bg);
    padding: 8px 0 12px;
  }

  .nav-links.open {
    display: flex;
  }

  .nav-wrap {
    flex-wrap: wrap;
  }
}

/* Topic chips (cross-topic navigation) */
.chip-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: center;
  margin: 0 0 26px;
}

.chip {
  display: inline-block;
  padding: 8px 14px;
  border-radius: 999px;
  border: 2px solid #e5e7eb;
  background: #fff;
  font-size: 15px;
  font-weight: 700;
  color: var(--ink);
  text-decoration: none;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s, color 0.15s;
}

.chip:hover {
  border-color: var(--accent, #6366f1);
}

.chip.active {
  background: var(--accent, #6366f1);
  border-color: var(--accent, #6366f1);
  color: #fff;
}

.chip-topic {
  padding: 6px 12px;
  font-size: 14px;
  background: transparent;
}

.chip-topic.active {
  background: var(--accent, #6366f1);
  border-color: var(--accent, #6366f1);
  color: #fff;
}

/* Subtopic sections */
.subtopic-section {
  margin-bottom: 30px;
}

.subtopic-title {
  font-size: 26px;
  margin: 0 0 14px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.subtopic-title .subtopic-emoji {
  font-size: 30px;
}

.fallback-msg {
  text-align: center;
  font-size: 22px;
  font-weight: 700;
  padding: 40px 20px;
  color: #6b7280;
}