*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --color-bg: #0f172a;
  --color-surface: #1e293b;
  --color-border: #334155;
  --color-primary: #6366f1;
  --color-primary-hover: #818cf8;
  --color-text: #f1f5f9;
  --color-text-muted: #94a3b8;
  --color-correct: #22c55e;
  --color-correct-bg: rgba(34, 197, 94, 0.1);
  --color-wrong: #ef4444;
  --color-wrong-bg: rgba(239, 68, 68, 0.1);
  --radius: 12px;
  --transition: 0.3s ease;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

.container {
  width: 100%;
  max-width: 640px;
  padding: 20px;
}

/* Screens */
.screen {
  display: none;
  animation: fadeIn 0.4s ease;
}

.screen.active {
  display: block;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

.hero-image {
  width: 100px;
  height: auto;
  margin-bottom: 20px;
}

/* Card */
.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 40px 32px;
  text-align: center;
}

h1 {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: 12px;
  line-height: 1.3;
}

.subtitle {
  color: var(--color-text-muted);
  font-size: 1.05rem;
  margin-bottom: 32px;
  line-height: 1.5;
}

/* Buttons */
.btn {
  display: inline-block;
  padding: 14px 32px;
  border: none;
  border-radius: 8px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background var(--transition), opacity var(--transition);
}

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

.btn-primary {
  background: var(--color-primary);
  color: #fff;
}

.btn-primary:hover:not(:disabled) {
  background: var(--color-primary-hover);
}

.btn-secondary {
  background: transparent;
  color: var(--color-primary);
  border: 2px solid var(--color-primary);
}

.btn-secondary:hover:not(:disabled) {
  background: rgba(99, 102, 241, 0.1);
}

/* Progress Bar */
.progress-bar {
  width: 100%;
  height: 6px;
  background: var(--color-surface);
  border-radius: 3px;
  margin-bottom: 24px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--color-primary);
  border-radius: 3px;
  transition: width 0.5s ease;
  width: 0%;
}

/* Question */
.question-count {
  display: inline-block;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 16px;
}

.question-text {
  font-size: 1.35rem;
  font-weight: 600;
  line-height: 1.4;
  margin-bottom: 28px;
}

/* Choices */
.choices {
  display: flex;
  flex-direction: row;
  gap: 12px;
  margin-bottom: 28px;
  justify-content: center;
}

.choice-btn {
  flex: 1;
  max-width: 200px;
  padding: 16px 20px;
  background: var(--color-bg);
  border: 2px solid var(--color-border);
  border-radius: 8px;
  color: var(--color-text);
  font-size: 1.1rem;
  font-weight: 600;
  text-align: center;
  cursor: pointer;
  transition: border-color var(--transition), background var(--transition);
}

.choice-btn:hover:not(:disabled) {
  border-color: var(--color-primary);
}

.choice-btn.selected {
  border-color: var(--color-primary);
  background: rgba(99, 102, 241, 0.1);
}

.choice-btn.correct {
  border-color: var(--color-correct);
  background: var(--color-correct-bg);
}

.choice-btn.wrong {
  border-color: var(--color-wrong);
  background: var(--color-wrong-bg);
}

.choice-btn:disabled {
  cursor: default;
}

/* Feedback */
.feedback {
  margin-top: 24px;
  animation: fadeIn 0.4s ease;
}

.feedback.hidden {
  display: none;
}

.feedback-icon {
  font-size: 2rem;
  margin-bottom: 8px;
}

.feedback-text {
  color: var(--color-text-muted);
  font-size: 0.95rem;
  margin-bottom: 12px;
  line-height: 1.5;
}

.btn-read-more {
  background: none;
  border: none;
  color: var(--color-primary);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  padding: 4px 8px;
  margin-bottom: 16px;
  display: inline-block;
  transition: color var(--transition);
}

.btn-read-more:hover {
  color: var(--color-primary-hover);
}

.full-explanation {
  text-align: left;
  color: var(--color-text-muted);
  font-size: 0.9rem;
  line-height: 1.6;
  margin-bottom: 20px;
  padding: 16px 20px;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  animation: fadeIn 0.4s ease;
}

.full-explanation p {
  margin-bottom: 12px;
}

.full-explanation p:last-child {
  margin-bottom: 0;
}

.full-explanation.hidden {
  display: none;
}

/* Results */
.score-display {
  font-size: 4rem;
  font-weight: 800;
  color: var(--color-primary);
  margin: 24px 0 8px;
}

.score-message {
  color: var(--color-text-muted);
  font-size: 1.1rem;
  margin-bottom: 32px;
}

/* Responsive */
@media (max-width: 480px) {
  .card {
    padding: 28px 20px;
  }

  h1 {
    font-size: 1.4rem;
  }

  .question-text {
    font-size: 1.15rem;
  }
}