:root {
  --bg: #f4f6fb;
  --surface: #ffffff;
  --ink: #1c2333;
  --ink-soft: #5b6478;
  --accent: #3457d5;
  --accent-soft: #dbe3ff;
  --good: #1f9d55;
  --bad: #d9453f;
  --muted: #b3b8c9;
  --card-back-1: #3457d5;
  --card-back-2: #6c8bff;
  --border: #e1e5f0;
  --radius: 14px;
  --font-body: "VT323", monospace;
  --font-pixel: "Press Start 2P", monospace;

  /* Categorical palette for color-coding matched pairs (validated for CVD
     separation on a light surface). Cycles past 8 for higher pair counts;
     the numbered badge on each card is the reliable identifier when colors repeat. */
  --pair-color-1: #2a78d6; /* blue */
  --pair-color-2: #eb6834; /* orange */
  --pair-color-3: #1baf7a; /* aqua */
  --pair-color-4: #eda100; /* yellow */
  --pair-color-5: #e87ba4; /* magenta */
  --pair-color-6: #008300; /* green */
  --pair-color-7: #4a3aa7; /* violet */
  --pair-color-8: #e34948; /* red */

  font-family: var(--font-body);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--ink);
  display: flex;
  justify-content: center;
  padding: 32px 16px;
  font-size: 1.25rem;
}

#app {
  width: 100%;
  max-width: 900px;
}

.hidden {
  display: none;
}

@keyframes screen-fade-in {
  from {
    opacity: 0;
    transform: translateY(6px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.screen:not(.hidden) {
  animation: screen-fade-in 0.35s ease both;
}

/* ---------- Setup screen ---------- */

#setup-screen {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 40px;
  text-align: center;
  max-width: 480px;
  margin: 60px auto 0;
}

h1 {
  margin: 0 0 16px;
  font-family: var(--font-pixel);
  font-size: 1.5rem;
  line-height: 1.5;
}

.subtitle {
  color: var(--ink-soft);
  margin: 0 0 28px;
  font-size: 1.15rem;
}

label, .field-label {
  display: block;
  text-align: left;
  font-family: var(--font-pixel);
  font-size: 0.65rem;
  letter-spacing: 0.02em;
  margin: 0 0 8px;
  color: var(--ink-soft);
}

.field-label {
  margin-top: 24px;
}

.checkbox-row {
  display: flex;
  align-items: center;
  gap: 8px;
  text-align: left;
  font-family: var(--font-body);
  font-size: 1.1rem;
  color: var(--ink-soft);
  margin-bottom: 4px;
  cursor: pointer;
}

.checkbox-row input {
  flex-shrink: 0;
  width: 18px;
  height: 18px;
  cursor: pointer;
}

#non-guest-fields.hidden {
  display: none;
}

#student-id,
.field-input {
  width: 100%;
  padding: 12px 14px;
  border-radius: 10px;
  border: 1px solid var(--border);
  font-family: var(--font-body);
  font-size: 1.3rem;
  outline: none;
  background: var(--surface);
  color: var(--ink);
}

.field-input {
  cursor: pointer;
}

#student-id:focus,
.field-input:focus {
  border-color: var(--accent);
}

.pill-group {
  display: flex;
  gap: 10px;
  justify-content: center;
}

.pill {
  flex: 1;
  padding: 14px 0;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--surface);
  font-family: var(--font-pixel);
  font-size: 0.7rem;
  color: var(--ink);
  cursor: pointer;
  transition: all 0.15s ease;
}

.pill:hover {
  border-color: var(--accent);
}

.pill.selected {
  background: var(--accent);
  border-color: var(--accent);
  color: white;
}

.primary-btn {
  margin-top: 28px;
  width: 100%;
  padding: 16px 0;
  border: none;
  border-radius: 10px;
  background: var(--accent);
  color: white;
  font-family: var(--font-pixel);
  font-size: 0.85rem;
  letter-spacing: 0.02em;
  cursor: pointer;
  transition: opacity 0.15s ease;
}

.primary-btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.primary-btn:not(:disabled):hover {
  opacity: 0.9;
}

.hint {
  margin: 10px 0 0;
  min-height: 1.1rem;
  font-size: 1rem;
  color: var(--ink-soft);
}

.text-btn {
  background: none;
  border: none;
  color: var(--ink-soft);
  font-family: var(--font-body);
  font-size: 1.1rem;
  cursor: pointer;
  text-decoration: underline;
}

/* ---------- Game screen ---------- */

#game-screen:not(.hidden) {
  display: flex;
  flex-direction: column;
  min-height: calc(100vh - 64px);
  min-height: calc(100dvh - 64px);
}

.game-header {
  display: flex;
  align-items: center;
  gap: 28px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px 20px;
  margin-bottom: 20px;
  flex-shrink: 0;
}

.header-item {
  display: flex;
  flex-direction: column;
  font-variant-numeric: tabular-nums;
}

.header-item .label {
  font-family: var(--font-pixel);
  font-size: 0.55rem;
  color: var(--ink-soft);
  text-transform: uppercase;
  letter-spacing: 0.03em;
  margin-bottom: 4px;
}

.header-item span:last-child {
  font-family: var(--font-pixel);
  font-size: 0.9rem;
}

.game-header #quit-btn {
  margin-left: auto;
}

.card-grid {
  flex: 1;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  justify-content: center;
  align-content: center;
  min-height: 0;
}

.card {
  aspect-ratio: 3 / 4;
  perspective: 800px;
  cursor: pointer;
}

.card.matched {
  cursor: default;
}

.card-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.4s cubic-bezier(0.4, 0.2, 0.2, 1);
  transform-style: preserve-3d;
}

.card.flipped .card-inner,
.card.matched .card-inner {
  transform: rotateY(180deg);
}

@keyframes match-pop {
  0% {
    transform: rotateY(180deg) scale(1);
  }
  40% {
    transform: rotateY(180deg) scale(1.12);
  }
  100% {
    transform: rotateY(180deg) scale(1);
  }
}

.card.match-pop .card-inner {
  animation: match-pop 0.45s ease;
}

.card-face {
  position: absolute;
  inset: 0;
  border-radius: 10px;
  backface-visibility: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
}

.card-back {
  background: linear-gradient(135deg, var(--card-back-1), var(--card-back-2));
  color: rgba(255, 255, 255, 0.85);
  font-family: var(--font-pixel);
  font-size: 1.3rem;
}

.card-front {
  transform: rotateY(180deg);
  background-color: #fafcff;
  background-image:
    linear-gradient(rgba(52, 87, 213, 0.08) 1px, transparent 1px),
    linear-gradient(90deg, rgba(52, 87, 213, 0.08) 1px, transparent 1px);
  background-size: 12px 12px;
  border: 2px solid var(--border);
  padding: 6px;
}

.card.matched .card-front {
  background-color: color-mix(in srgb, var(--pair-color, var(--good)) 14%, white);
  border-color: var(--pair-color, var(--good));
}

.pair-badge {
  position: absolute;
  top: 3px;
  left: 3px;
  min-width: 16px;
  height: 16px;
  padding: 0 3px;
  border-radius: 5px;
  background: var(--pair-color, var(--good));
  color: white;
  font-family: var(--font-pixel);
  font-size: 0.5rem;
  display: flex;
  align-items: center;
  justify-content: center;
  line-height: 1;
}

.card-front .katex {
  font-size: 1rem;
  background: rgba(255, 255, 255, 0.85);
  padding: 2px 6px;
  border-radius: 6px;
}

@media (min-width: 600px) {
  .card-front .katex {
    font-size: 1.15rem;
  }
}

/* ---------- Win screen ---------- */

#win-screen {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 40px;
  max-width: 520px;
  margin: 40px auto 0;
  text-align: center;
}

.tab-group {
  display: flex;
  gap: 8px;
  justify-content: center;
  margin-top: 8px;
}

.tab {
  padding: 10px 18px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--surface);
  font-family: var(--font-pixel);
  font-size: 0.6rem;
  color: var(--ink-soft);
  cursor: pointer;
}

.tab.active {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent);
}

.placeholder-note {
  font-size: 0.78rem;
  color: var(--ink-soft);
  margin: 12px 0;
}

#leaderboard-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 8px;
}

#leaderboard-table th,
#leaderboard-table td {
  text-align: left;
  padding: 8px 10px;
  border-bottom: 1px solid var(--border);
  font-size: 1.15rem;
}

#leaderboard-table th {
  color: var(--ink-soft);
  font-family: var(--font-pixel);
  font-size: 0.55rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.win-actions {
  margin-top: 24px;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

/* ---------- Round 2 screen ---------- */

#round2-screen {
  max-width: 520px;
  margin: 0 auto;
}

#round2-screen .game-header {
  margin-bottom: 20px;
}

#r2-complete {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 40px;
  text-align: center;
}

.r2-play .subtitle {
  text-align: center;
}

.r2-progress {
  height: 10px;
  border-radius: 999px;
  background: var(--border);
  overflow: hidden;
}

.r2-progress-fill {
  height: 100%;
  width: 0%;
  background: var(--good);
  border-radius: 999px;
  transition: width 0.3s ease;
}

#r2-instructions-notation .katex {
  font-size: 1rem;
}

.r2-equation {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  margin-top: 12px;
}

.r2-equals {
  font-family: var(--font-pixel);
  font-size: 1.2rem;
  color: var(--muted);
  flex-shrink: 0;
  transition: color 0.15s ease;
}

.r2-equals.correct {
  color: var(--good);
}

.r2-equals.incorrect {
  color: var(--bad);
}

.r2-side {
  flex: 1;
  min-height: 120px;
  padding: 16px 10px;
  border-radius: var(--radius);
  border: 2px solid var(--border);
  background-color: #fafcff;
  background-image:
    linear-gradient(rgba(52, 87, 213, 0.08) 1px, transparent 1px),
    linear-gradient(90deg, rgba(52, 87, 213, 0.08) 1px, transparent 1px);
  background-size: 12px 12px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: border-color 0.15s ease, background-color 0.15s ease;
}

.r2-side:hover {
  border-color: var(--accent);
}

.r2-side .katex {
  font-size: 1.1rem;
}

@keyframes r2-shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-6px); }
  75% { transform: translateX(6px); }
}

.r2-side.incorrect {
  border-color: var(--bad);
  background-color: color-mix(in srgb, var(--bad) 12%, white);
  animation: r2-shake 0.3s ease;
}

.r2-side.correct {
  border-color: var(--good);
  background-color: color-mix(in srgb, var(--good) 14%, white);
}

.r2-side:disabled {
  cursor: default;
}