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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background-color: #f4f6f9;
  color: #333;
  padding: 20px;
  line-height: 1.6;
}

.container {
  max-width: 680px;
  margin: 0 auto;
}

header {
  text-align: center;
  margin-bottom: 20px;
}

h1 {
  font-size: 24px;
  color: #1a202c;
  margin-bottom: 6px;
}

.subtitle {
  font-size: 14px;
  color: #718096;
}

.card {
  background: white;
  padding: 20px 24px;
  border-radius: 12px;
  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  margin-bottom: 16px;
}

.form-group {
  margin-bottom: 16px;
}

label {
  display: block;
  font-weight: 600;
  font-size: 14px;
  margin-bottom: 6px;
  color: #4a5568;
}

select {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid #cbd5e0;
  border-radius: 8px;
  font-size: 15px;
  color: #2d3748;
  background-color: #fff;
  cursor: pointer;
}

.btn-group {
  display: flex;
  gap: 12px;
}

.btn {
  flex: 1;
  padding: 12px 16px;
  font-size: 15px;
  font-weight: 600;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: background-color 0.2s, transform 0.1s;
}

.btn:active {
  transform: scale(0.98);
}

.btn.primary {
  background-color: #3182ce;
  color: white;
}

.btn.primary:hover {
  background-color: #2b6cb0;
}

.btn.secondary {
  background-color: #e2e8f0;
  color: #4a5568;
}

.btn.secondary:hover {
  background-color: #cbd5e0;
}

.btn:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

.status {
  text-align: center;
  color: #718096;
  font-size: 15px;
  padding: 12px 0;
}

.question-text {
  font-size: 17px;
  color: #2d3748;
  margin-bottom: 16px;
}

.options-container {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.option-btn {
  width: 100%;
  text-align: left;
  padding: 12px 16px;
  background-color: #f7fafc;
  border: 1px solid #e2e8f0;
  border-radius: 8px;
  font-size: 15px;
  color: #2d3748;
  cursor: pointer;
  transition: all 0.2s;
}

.option-btn:hover {
  background-color: #edf2f7;
  border-color: #cbd5e0;
}

.explanation {
  margin-top: 20px;
  padding: 16px;
  border-radius: 8px;
  font-size: 15px;
  line-height: 1.6;
}

.explanation.correct {
  background-color: #f0fff4;
  border: 1px solid #c6f6d5;
  color: #22543d;
}

.explanation.incorrect {
  background-color: #fff5f5;
  border: 1px solid #fed7d7;
  color: #742a2a;
}

.hidden {
  display: none;
}