:root {
  --blue: #1a6dff;
  --blue-dark: #1450c8;
  --text: #111c2f;
  --muted: #6b768c;
  font-family: "PingFang SC", "Microsoft YaHei", Arial, sans-serif;
}

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

body {
  margin: 0;
  min-height: 100vh;
  background: #f7f9ff;
  color: var(--text);
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 20px 16px 120px;
}

.quiz-container {
  width: min(640px, 100%);
  background: #fff;
  border-radius: 28px;
  padding: 32px 28px 24px;
  box-shadow: 0 24px 60px rgba(10, 40, 110, 0.08);
}

.quiz-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 24px;
  flex-wrap: wrap;
  gap: 8px;
}

.quiz-title {
  font-size: 20px;
  font-weight: 600;
}

.progress {
  font-size: 15px;
  color: var(--muted);
}

.question-area {
  margin-bottom: 28px;
}

.question-text {
  font-size: 22px;
  line-height: 1.4;
}

.options {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.option-btn {
  width: 100%;
  padding: 16px 18px;
  border-radius: 18px;
  border: 1px solid #dbe4ff;
  background: #f4f7ff;
  font-size: 16px;
  text-align: left;
  cursor: pointer;
  transition: background 0.2s ease, color 0.2s ease, border 0.2s ease;
}

.option-btn:hover {
  border-color: var(--blue);
}

.option-btn.selected {
  background: var(--blue);
  color: #fff;
  border-color: var(--blue-dark);
  box-shadow: 0 8px 20px rgba(26, 109, 255, 0.3);
}

.nav-actions {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%);
  width: min(640px, calc(100% - 32px));
  display: flex;
  gap: 12px;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(6px);
  border-radius: 18px;
  padding: 16px;
  box-shadow: 0 20px 40px rgba(8, 25, 80, 0.12);
}

.nav-btn {
  flex: 1;
  border: none;
  border-radius: 999px;
  padding: 16px;
  font-size: 16px;
  cursor: pointer;
  background: #e4ebff;
  color: var(--text);
  transition: background 0.2s ease, color 0.2s ease;
}

.nav-btn.primary {
  background: var(--blue);
  color: #fff;
  font-weight: 600;
}

.nav-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

@media (max-width: 480px) {
  body {
    padding: 16px 12px 110px;
  }

  .quiz-container {
    padding: 24px 20px 18px;
  }

  .question-text {
    font-size: 20px;
  }

  .option-btn {
    font-size: 15px;
  }
}