:root {
  /* Deep-space theme — matches the game canvas (#1B1E45 → #0A0C22) */
  --bg-a: #070919;
  --bg-b: #111536;
  --card: #151A3A;
  --card-tint: #1C2250;
  --ink: #E9EBFF;
  --ink-soft: #9CA2CC;
  --rule: #2B3168;

  --primary: #8B7BFF;
  --primary-dark: #C3BAFF;
  --accent2: #00D4B8;
  --break: #FF7A5C;
  --gold: #F5D76E;
  --shield: #4FD8E8;

  --correct: #34D399;
  --correct-bg: rgba(52, 211, 153, 0.14);
  --incorrect: #FF5C74;
  --incorrect-bg: rgba(255, 92, 116, 0.14);

  --shadow: 0 8px 26px rgba(0, 0, 0, 0.45);
  --shadow-sm: 0 2px 10px rgba(0, 0, 0, 0.35);

  --serif: Georgia, 'Iowan Old Style', 'Times New Roman', serif;
  --sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Ubuntu, sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  color: var(--ink);
  font-family: var(--sans);
  line-height: 1.5;
  background-color: var(--bg-a);
  /* starfield (three tiled layers of different density) over a faint nebula */
  background-image:
    radial-gradient(1.2px 1.2px at 20px 30px, #fff 50%, transparent 51%),
    radial-gradient(1px 1px at 120px 80px, rgba(255,255,255,.8) 50%, transparent 51%),
    radial-gradient(1px 1px at 70px 150px, rgba(255,255,255,.6) 50%, transparent 51%),
    radial-gradient(1.5px 1.5px at 160px 190px, rgba(190,200,255,.9) 50%, transparent 51%),
    radial-gradient(1px 1px at 40px 110px, rgba(255,255,255,.5) 50%, transparent 51%),
    radial-gradient(ellipse 70% 45% at 85% 10%, rgba(139, 123, 255, 0.20), transparent 70%),
    radial-gradient(ellipse 60% 40% at 5% 75%, rgba(0, 212, 184, 0.12), transparent 70%),
    linear-gradient(180deg, var(--bg-b) 0%, var(--bg-a) 60%);
  background-size: 173px 191px, 239px 211px, 97px 131px, 311px 283px, 151px 163px, 100% 100%, 100% 100%, 100% 100%;
  background-attachment: fixed;
}

#app {
  max-width: 640px;
  margin: 0 auto;
  padding: 0 20px 60px;
}

/* ---- Masthead ---- */
.masthead {
  padding: 26px 0 16px;
  margin-bottom: 28px;
}
.masthead-inner {
  display: flex;
  align-items: baseline;
  gap: 10px;
}
.wordmark {
  font-family: var(--serif);
  font-size: 1.6rem;
  font-weight: 700;
  background: linear-gradient(100deg, var(--primary), var(--accent2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.wordmark-accent { color: var(--break); -webkit-text-fill-color: var(--break); }
.tagline {
  font-size: 0.85rem;
  color: var(--ink-soft);
  font-style: italic;
}
.progress-track {
  margin-top: 14px;
  height: 8px;
  background: rgba(139, 123, 255, 0.16);
  border-radius: 5px;
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  width: 0%;
  background: linear-gradient(90deg, var(--primary), var(--accent2));
  border-radius: 5px;
  transition: width 0.35s ease;
}

/* ---- Screens ---- */
.screen.hidden { display: none; }

h1 {
  font-family: var(--serif);
  font-size: 1.8rem;
  line-height: 1.25;
  margin: 0 0 14px;
  color: var(--primary-dark);
}
.lede {
  font-size: 1.02rem;
  color: var(--ink);
  max-width: 52ch;
}
.rules {
  margin: 18px 0 26px;
  padding-left: 20px;
  color: var(--ink-soft);
}
.rules li { margin-bottom: 6px; }

/* ---- Difficulty selector ---- */
.difficulty-select {
  margin: 4px 0 22px;
}
.difficulty-label {
  display: block;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--ink-soft);
  margin-bottom: 8px;
}
.difficulty-options {
  display: flex;
  gap: 8px;
}
.diff-btn {
  font-family: var(--sans);
  font-size: 0.88rem;
  font-weight: 700;
  padding: 9px 18px;
  border-radius: 999px;
  border: 1.5px solid var(--rule);
  background: var(--card);
  color: var(--ink-soft);
  cursor: pointer;
  transition: border-color 0.15s ease, color 0.15s ease, background 0.15s ease;
}
.diff-btn:hover { border-color: var(--primary); }
.diff-btn.active {
  border-color: transparent;
  background: linear-gradient(100deg, var(--primary), var(--accent2));
  color: #fff;
}

.btn {
  font-family: var(--sans);
  font-size: 0.95rem;
  font-weight: 700;
  padding: 13px 30px;
  border-radius: 999px;
  border: none;
  cursor: pointer;
  transition: transform 0.1s ease, box-shadow 0.15s ease, background 0.15s ease;
}
.btn:active { transform: scale(0.97); }
.btn-primary {
  background: linear-gradient(100deg, var(--primary), var(--accent2));
  color: #fff;
  box-shadow: var(--shadow-sm);
}
.btn-primary:hover { box-shadow: var(--shadow); transform: translateY(-1px); }
.btn-secondary {
  background: var(--card);
  color: var(--primary-dark);
  border: 1.5px solid var(--primary);
}
.btn-secondary:hover { background: var(--card-tint); }

/* ---- Puzzle head ---- */
.puzzle-head {
  display: flex;
  flex-direction: column;
  gap: 4px;
  margin-bottom: 16px;
}
.puzzle-count {
  display: inline-block;
  align-self: flex-start;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--primary-dark);
  background: rgba(139, 123, 255, 0.18);
  padding: 3px 10px;
  border-radius: 999px;
}
.puzzle-title {
  font-family: var(--serif);
  font-size: 1.35rem;
  margin: 4px 0 0;
  color: var(--ink);
}

/* ---- Target card / reaction row ---- */
.target-card {
  background: var(--card);
  border: 1px solid var(--rule);
  border-radius: 16px;
  padding: 20px 12px 16px;
  margin-bottom: 18px;
  box-shadow: var(--shadow);
}
.reaction-row {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  flex-wrap: wrap;
}
.reaction-mol {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
}
.mol-cap {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--ink-soft);
}
.reaction-mol svg { max-width: 100%; height: auto; }
.reaction-arrow {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-width: 56px;
  padding-top: 14px;
}
.arrow-q {
  font-family: var(--serif);
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 4px;
}
.arrow-line {
  display: flex;
  align-items: center;
}
.arrow-shaft {
  width: 32px;
  height: 2px;
  background: var(--primary);
}
.arrow-head {
  width: 0;
  height: 0;
  border-top: 5px solid transparent;
  border-bottom: 5px solid transparent;
  border-left: 7px solid var(--primary);
}
.hint {
  text-align: center;
  font-size: 0.8rem;
  font-style: italic;
  color: var(--ink-soft);
  margin: 14px 0 0;
}
.hint.hidden { display: none; }

.instruction {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--ink-soft);
  margin: 0 0 10px;
}

/* ---- Options ---- */
.options-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
@media (max-width: 480px) {
  .options-grid { grid-template-columns: 1fr; }
}
.option-card {
  background: var(--card);
  border: 2px solid var(--rule);
  border-radius: 14px;
  padding: 14px 10px;
  cursor: pointer;
  text-align: left;
  transition: border-color 0.15s ease, transform 0.12s ease, box-shadow 0.15s ease;
  font-family: var(--sans);
  box-shadow: var(--shadow-sm);
}
.option-card:hover:not(:disabled) {
  border-color: var(--primary);
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}
.option-card:disabled { cursor: default; }
.reagent-option {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 64px;
  text-align: center;
}
.reagent-text {
  font-family: var(--serif);
  font-size: 0.98rem;
  font-weight: 700;
  color: var(--ink);
  line-height: 1.35;
}
.option-card.correct {
  border-color: var(--correct);
  background: var(--correct-bg);
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}
.option-card.incorrect {
  border-color: var(--incorrect);
  background: var(--incorrect-bg);
}

/* ---- Feedback ---- */
.feedback {
  margin-top: 20px;
  padding: 18px;
  border-radius: 14px;
  background: var(--card);
  border: 1px solid var(--rule);
  box-shadow: var(--shadow-sm);
}
.feedback.hidden { display: none; }
#feedback-text {
  margin: 0 0 14px;
  font-size: 0.95rem;
}

/* ---- End screen ---- */
.end-score {
  font-family: var(--serif);
  font-size: 1.15rem;
  color: var(--primary-dark);
  margin-bottom: 24px;
}
.end-review {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 28px;
}
.review-row {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 12px;
  border-radius: 10px;
  background: var(--card);
  border: 1px solid var(--rule);
  font-size: 0.9rem;
  box-shadow: var(--shadow-sm);
}
.review-mark {
  font-weight: 700;
  width: 18px;
  text-align: center;
}
.review-row.correct .review-mark { color: var(--correct); }
.review-row.incorrect .review-mark { color: var(--incorrect); }
.review-row {
  flex-direction: column;
  align-items: stretch;
  gap: 4px;
}
.review-row-main {
  display: flex;
  align-items: center;
  gap: 10px;
}
.review-detail {
  font-size: 0.8rem;
  color: var(--ink-soft);
  padding-left: 28px;
}
.review-detail strong { color: var(--ink); }

/* ---- Structures (chem.js draws in currentColor) ---- */
.mol { color: var(--ink); display: block; }

/* ---- Invaders game additions ---- */
.hud {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 6px;
  margin-bottom: 10px;
  font-weight: 700;
  font-size: 0.85rem;
  color: var(--primary-dark);
}
.hud-item {
  background: var(--card);
  border-radius: 999px;
  padding: 6px 12px;
  box-shadow: var(--shadow-sm);
}
.hud-score { color: var(--accent2); }
.hud-btn {
  border: none;
  font-family: var(--sans);
  font-weight: 700;
  font-size: 0.85rem;
  cursor: pointer;
  color: var(--primary-dark);
}
.hud-btn:active { background: var(--primary); color: #fff; }

.game-wrap {
  position: relative;
  display: flex;
  justify-content: center;
  margin-bottom: 14px;
}
.game-frame {
  position: relative;
  padding: 9px;
  border-radius: 20px;
  background: linear-gradient(135deg, var(--primary), var(--accent2));
  box-shadow: var(--shadow);
}
#game-canvas {
  background: #0A0C22;
  border-radius: 13px;
  max-width: 100%;
  height: auto;
  display: block;
}
.frame-hex {
  position: absolute;
  width: 14px;
  height: 14px;
  background: var(--card);
  border: 2px solid var(--primary);
  clip-path: polygon(25% 3%, 75% 3%, 100% 50%, 75% 97%, 25% 97%, 0% 50%);
  z-index: 2;
}
.frame-hex.tl { top: 2px; left: 2px; }
.frame-hex.tr { top: 2px; right: 2px; }
.frame-hex.bl { bottom: 2px; left: 2px; }
.frame-hex.br { bottom: 2px; right: 2px; }

.pause-overlay {
  position: absolute;
  top: 9px; left: 9px; right: 9px; bottom: 9px;
  border-radius: 13px;
  background: rgba(10, 12, 34, 0.72);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 3;
}
.pause-overlay.hidden { display: none; }
.pause-card {
  text-align: center;
}
.pause-card h3 {
  font-family: var(--serif);
  color: #fff;
  font-size: 1.4rem;
  margin: 0 0 14px;
}

.game-wrap.hidden { display: none; }
.controls.hidden { display: none; }

.controls {
  display: grid;
  grid-template-columns: 64px 1fr 64px;
  gap: 8px;
  align-items: center;
  margin-top: 4px;
}
.ctl-btn {
  font-size: 1.1rem;
  font-weight: 700;
  border: none;
  border-radius: 10px;
  background: var(--card);
  color: var(--primary-dark);
  box-shadow: var(--shadow-sm);
  cursor: pointer;
  padding: 14px 0;
}
.ctl-btn:active { background: var(--primary); color: #fff; }
.ctl-fire {
  background: linear-gradient(100deg, var(--primary), var(--accent2));
  color: #fff;
}

@media (min-width: 620px) {
  .controls { display: none; } /* desktop: keyboard only, saves space */
}

/* The quiz takes over the full app width while it's up — game canvas and
   controls hide (see game.js) so molecules and options stay readable on
   a small phone screen, same pattern as the maze checkpoint overlay. */
.quiz-overlay {
  display: flex;
  flex-direction: column;
  gap: 12px;
}
.quiz-overlay.hidden { display: none; }

/* ---- Space intro ---- */
.intro { text-align: center; }
.intro-hero {
  display: flex;
  justify-content: center;
  margin: 4px 0 14px;
}
.hero-invader {
  color: var(--accent2);
  filter: drop-shadow(0 0 10px rgba(0, 212, 184, 0.55));
  animation: hover-bob 2.4s ease-in-out infinite;
}
@keyframes hover-bob {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-5px); }
}
@media (prefers-reduced-motion: reduce) { .hero-invader { animation: none; } }
.intro h1 {
  font-size: 2rem;
  color: #fff;
  text-shadow: 0 0 18px rgba(139, 123, 255, 0.55);
  margin-bottom: 8px;
}
.intro .lede { margin: 0 auto 20px; color: var(--ink-soft); }

.intro-tiles {
  display: grid;
  gap: 10px;
  text-align: left;
  margin-bottom: 14px;
}
.tile {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 11px 14px;
  background: rgba(21, 26, 58, 0.82);
  border: 1px solid var(--rule);
  border-radius: 14px;
}
.tile p { margin: 0; font-size: 0.88rem; color: var(--ink-soft); line-height: 1.4; }
.tile strong { color: var(--ink); }
.tile-icon {
  flex: 0 0 auto;
  width: 38px;
  height: 38px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 800;
}
.icon-capsule {
  border-radius: 50%;
  background: var(--gold);
  color: #10132A;
  font-family: var(--serif);
  font-size: 1.1rem;
  box-shadow: 0 0 12px rgba(245, 215, 110, 0.5);
}
.icon-tiers {
  width: auto;
  min-width: 38px;
  padding: 0 6px;
  gap: 3px;
  font-size: 0.95rem;
  background: #0A0C22;
  border-radius: 10px;
  border: 1px solid var(--rule);
}
.icon-tiers .t0 { color: #8A8FA8; }
.icon-tiers .t1 { color: #8B7BFF; }
.icon-tiers .t2 { color: #00BFA6; }
.icon-shield { color: var(--shield); filter: drop-shadow(0 0 6px rgba(79, 216, 232, 0.45)); }
.intro-meta {
  font-size: 0.78rem;
  color: var(--ink-soft);
  margin: 0 0 20px;
}
.intro .difficulty-select { margin-bottom: 22px; }
.intro .difficulty-options { justify-content: center; }
.btn-launch {
  padding: 14px 48px;
  font-size: 1.05rem;
  letter-spacing: 0.04em;
  box-shadow: 0 0 22px rgba(0, 212, 184, 0.35);
}
.btn-primary:hover { box-shadow: 0 0 26px rgba(139, 123, 255, 0.5); }