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

:root {
  --quiz-primary: #1e3a8a;
  --quiz-primary-hover: #1e40af;
  --quiz-primary-light: #dbeafe;
  --quiz-success: hsl(142 76% 45%);
  --quiz-success-light: hsl(142 76% 95%);
  --quiz-error: hsl(0 84% 60%);
  --quiz-error-light: hsl(0 84% 95%);
  --quiz-background: hsl(220 20% 98%);
  --quiz-card: hsl(220 15% 100%);
  --quiz-text: hsl(220 20% 15%);
  --quiz-text-muted: hsl(220 15% 45%);
  --quiz-border: hsl(220 15% 88%);
  --quiz-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
  --quiz-shadow-lg: 0 4px 16px rgba(0, 0, 0, 0.12);
  --quiz-radius: 12px;
  --quiz-radius-sm: 8px;
  --quiz-transition: all 0.15s ease;
}

.dark {
  --quiz-primary: hsl(221 75% 65%);
  --quiz-primary-hover: hsl(221 75% 70%);
  --quiz-primary-light: hsl(221 30% 25%);
  --quiz-success: hsl(142 45% 55%);
  --quiz-success-light: hsl(142 30% 20%);
  --quiz-error: hsl(0 65% 65%);
  --quiz-error-light: hsl(0 30% 20%);
  --quiz-background: hsl(220 15% 12%);
  --quiz-card: hsl(220 12% 16%);
  --quiz-text: hsl(220 15% 92%);
  --quiz-text-muted: hsl(220 12% 70%);
  --quiz-border: hsl(220 10% 25%);
  --quiz-shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
  --quiz-shadow-lg: 0 4px 16px rgba(0, 0, 0, 0.4);
}

body {
  font-family: 'Poppins', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--quiz-background);
  color: var(--quiz-text);
  line-height: 1.6;
  min-height: 100vh;
  padding: 20px;
}

.quiz-container {
  max-width: 800px;
  margin: 0 auto;
  padding-bottom: 60px;
  padding-top: 130px; /* desktop */
}

/* ================================
   STICKY HEADER
   ================================ */
.sticky-header-wrapper {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: var(--quiz-background);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--quiz-border);
}

.sticky-header-container {
  max-width: 800px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Nav Links */
.nav-links {
  display: flex;
  justify-content: space-evenly;
  padding: 8px 0;
  max-width: 500px;
  margin: 0 auto;
}

.nav-link {
  color: var(--quiz-primary);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  padding: 6px 16px;
  border-radius: var(--quiz-radius-sm);
  transition: var(--quiz-transition);
  text-align: center;
}

.nav-link:hover {
  background: var(--quiz-primary-light);
  color: var(--quiz-primary-hover);
}

/* Quiz Header */
.quiz-header {
  padding: 8px 0 10px;
}

/* ================================
   DESKTOP/TABLET: 3-column layout
   Timer | Title+Subtitle | Theme
   ================================ */
.quiz-header-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 8px;
}

.quiz-header-left {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: flex-start;
}

.quiz-header-center {
  flex: 2;
  text-align: center;
}

.quiz-header-right {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: flex-end;
}

/* Timer */
.timer-display {
  font-size: 14px;
  font-weight: 600;
  color: white;
  background: var(--quiz-primary);
  padding: 5px 12px;
  border-radius: 20px;
  box-shadow: 0 2px 8px rgba(109, 40, 217, 0.3);
  white-space: nowrap;
}

/* Theme Switcher */
.theme-switcher {
  background: var(--quiz-card);
  color: var(--quiz-primary);
  border: 2px solid var(--quiz-border);
  width: 40px;
  height: 40px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: var(--quiz-transition);
  box-shadow: var(--quiz-shadow);
  font-size: 18px;
  flex-shrink: 0;
}

.theme-switcher:hover {
  background: var(--quiz-primary);
  color: white;
  border-color: var(--quiz-primary);
  transform: rotate(15deg) scale(1.05);
}

.theme-switcher:active {
  transform: rotate(15deg) scale(0.95);
}

/* Title & Subtitle */
.quiz-title {
  font-size: 20px;
  font-weight: 700;
  margin-bottom: 2px;
  background: linear-gradient(135deg, var(--quiz-primary) 0%, #2563eb 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1.3;
}

.quiz-subtitle {
  color: var(--quiz-text-muted);
  font-size: 12px;
  font-weight: 400;
}

/* Progress Bar */
.progress-bar {
  background: var(--quiz-border);
  height: 5px;
  border-radius: 3px;
  overflow: hidden;
  box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.1);
}

.progress-fill {
  background: linear-gradient(90deg, var(--quiz-primary) 0%, #2563eb 100%);
  height: 100%;
  width: 0%;
  transition: width 0.2s ease;
  border-radius: 3px;
}

/* ================================
   QUIZ CONTENT
   ================================ */
.quiz-content {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.question-card {
  background: var(--quiz-card);
  border-radius: var(--quiz-radius);
  padding: 28px;
  box-shadow: var(--quiz-shadow);
  border: 1px solid var(--quiz-border);
  transition: border-color 0.2s ease;
}

.question-card:hover {
  border-color: hsl(250 95% 90%);
}

.question-header {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  margin-bottom: 24px;
}

.question-number {
  background: var(--quiz-primary);
  color: white;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 600;
  font-size: 14px;
  flex-shrink: 0;
}

.question-text {
  font-size: 16px;
  font-weight: 500;
  color: var(--quiz-text);
  line-height: 1.5;
  flex: 1;
}

.question-image {
  max-width: 100%;
  height: auto;
  border-radius: var(--quiz-radius-sm);
  margin-top: 16px;
  box-shadow: var(--quiz-shadow);
}

@media (max-width: 1024px) {
  .question-image {
    width: calc(100% + 48px);
    margin-left: -24px;
    margin-right: -24px;
    border-radius: 0;
  }
}

.options-container {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 20px;
}

.option-label {
  display: flex;
  align-items: center;
  padding: 12px 16px;
  border: 2px solid var(--quiz-border);
  border-radius: var(--quiz-radius-sm);
  cursor: pointer;
  transition: var(--quiz-transition);
  background: var(--quiz-card);
  position: relative;
  overflow: hidden;
}

.option-label:hover { border-color: var(--quiz-primary); background: var(--quiz-primary-light); }
.option-label.disabled { cursor: not-allowed; opacity: 0.7; }
.option-label.correct { background: var(--quiz-success-light); border-color: var(--quiz-success); }
.option-label.incorrect { background: var(--quiz-error-light); border-color: var(--quiz-error); }

.option-radio {
  appearance: none;
  width: 20px;
  height: 20px;
  border: 2px solid var(--quiz-border);
  border-radius: 50%;
  margin-right: 12px;
  position: relative;
  cursor: pointer;
  transition: var(--quiz-transition);
  flex-shrink: 0;
}

.option-radio:checked { border-color: var(--quiz-primary); }
.option-radio:checked::after {
  content: '';
  position: absolute;
  width: 10px; height: 10px;
  background: var(--quiz-primary);
  border-radius: 50%;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
}

.option-label.correct .option-radio { border-color: var(--quiz-success); }
.option-label.correct .option-radio::after { background: var(--quiz-success); }
.option-label.incorrect .option-radio { border-color: var(--quiz-error); }
.option-label.incorrect .option-radio::after { background: var(--quiz-error); }

.option-text {
  font-size: 14px;
  font-weight: 400;
  color: var(--quiz-text);
  flex: 1;
}

.feedback-icon {
  margin-left: auto;
  font-size: 20px;
  font-weight: 600;
  display: none;
}

.option-label.correct .correct-icon,
.option-label.incorrect .incorrect-icon { display: block; }

.question-actions {
  display: flex;
  gap: 12px;
  align-items: center;
}

.view-solution-btn {
  background: var(--quiz-primary);
  color: white;
  border: none;
  padding: 10px 20px;
  border-radius: var(--quiz-radius-sm);
  font-size: 14px;
  font-weight: 500;
  font-family: 'Poppins', sans-serif;
  cursor: pointer;
  transition: var(--quiz-transition);
  display: inline-flex;
  align-items: center;
  gap: 8px;
  box-shadow: 0 2px 8px rgba(109, 40, 217, 0.3);
}

.view-solution-btn:hover { background: var(--quiz-primary-hover); }
.view-solution-btn::after { content: '▼'; font-size: 12px; transition: transform 0.3s ease; }
.view-solution-btn.active::after { transform: rotate(180deg); }

.reset-btn {
  background: var(--quiz-card);
  color: var(--quiz-text);
  border: 2px solid var(--quiz-border);
  padding: 10px 20px;
  border-radius: var(--quiz-radius-sm);
  font-size: 14px;
  font-weight: 500;
  font-family: 'Poppins', sans-serif;
  cursor: pointer;
  transition: var(--quiz-transition);
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

.reset-btn:hover:not(:disabled) { background: var(--quiz-primary-light); border-color: var(--quiz-primary); }
.reset-btn:disabled { opacity: 0.5; cursor: not-allowed; }

.solution-section {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.2s ease;
  margin-top: 0;
}

.solution-section.visible { max-height: 2000px; margin-top: 20px; }

.solution-content {
  background: linear-gradient(135deg, var(--quiz-primary-light) 0%, #e0e7ff 100%);
  border-left: 4px solid var(--quiz-primary);
  padding: 24px;
  border-radius: var(--quiz-radius-sm);
}

.solution-title {
  font-size: 16px;
  font-weight: 600;
  color: var(--quiz-primary);
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.solution-title::before { content: '💡'; font-size: 18px; }

.solution-text {
  font-size: 14px;
  line-height: 1.7;
  color: var(--quiz-text);
}

.solution-text p { margin-bottom: 12px; }

.solution-image {
  max-width: 100%;
  height: auto;
  border-radius: var(--quiz-radius-sm);
  margin-top: 16px;
  margin-bottom: 16px;
  box-shadow: var(--quiz-shadow);
}

.solution-text img {
  max-width: 100%;
  height: auto;
  border-radius: var(--quiz-radius-sm);
  margin: 16px 0;
  box-shadow: var(--quiz-shadow);
  display: block;
}

@media (max-width: 1024px) {
  .solution-text img,
  .solution-image {
    width: calc(100% + 48px);
    margin-left: -24px;
    margin-right: -24px;
    border-radius: 0;
    margin-top: 16px;
    margin-bottom: 16px;
  }
}

.quiz-actions {
  display: flex;
  gap: 16px;
  justify-content: center;
  margin-top: 32px;
  margin-bottom: 32px;
}

.submit-btn {
  background: var(--quiz-success);
  color: white;
  border: none;
  padding: 14px 32px;
  border-radius: var(--quiz-radius-sm);
  font-size: 16px;
  font-weight: 600;
  font-family: 'Poppins', sans-serif;
  cursor: pointer;
  transition: var(--quiz-transition);
  box-shadow: 0 2px 8px rgba(34, 197, 94, 0.3);
}

.submit-btn:hover { background: hsl(142 76% 40%); }

.reset-all-btn {
  background: var(--quiz-card);
  color: var(--quiz-text);
  border: 2px solid var(--quiz-border);
  padding: 14px 32px;
  border-radius: var(--quiz-radius-sm);
  font-size: 16px;
  font-weight: 600;
  font-family: 'Poppins', sans-serif;
  cursor: pointer;
  transition: var(--quiz-transition);
}

.reset-all-btn:hover { background: var(--quiz-primary-light); border-color: var(--quiz-primary); }

.quiz-footer {
  background: var(--quiz-card);
  padding: 32px;
  border-radius: var(--quiz-radius);
  box-shadow: var(--quiz-shadow-lg);
  margin-top: 32px;
  text-align: center;
}

.score-display {
  font-size: 36px;
  font-weight: 700;
  background: linear-gradient(135deg, var(--quiz-primary) 0%, #2563eb 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 8px;
}

.score-text { font-size: 16px; color: var(--quiz-text-muted); font-weight: 500; }
.score-breakdown { margin-top: 12px; font-size: 14px; color: var(--quiz-text-muted); }

/* ================================
   MOBILE: max-width 640px
   Timer + Theme side by side
   Title below
   ================================ */
@media (max-width: 640px) {
  body { padding: 8px; }

  .quiz-container { padding-top: 140px; }

  .sticky-header-container { padding: 0 12px; }

  .nav-links { padding: 5px 0 4px; max-width: 100%; }
  .nav-link { font-size: 12px; padding: 3px 6px; }

  .quiz-header { padding: 5px 0 7px; }

  /* Mobile: stack vertically, timer+theme on top row */
  .quiz-header-top {
    flex-direction: column;
    align-items: center;
    gap: 4px;
    margin-bottom: 5px;
  }

  /* Timer + Theme side by side on mobile */
  .quiz-header-left,
  .quiz-header-right {
    flex: unset;
  }

  /* Wrap timer and theme in a row on mobile */
  .quiz-header-top {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    grid-template-areas:
      "timer . theme"
      "center center center";
    align-items: center;
    gap: 6px;
    margin-bottom: 5px;
  }

  .quiz-header-left  { grid-area: timer;  justify-content: flex-start; }
  .quiz-header-center { grid-area: center; text-align: center; }
  .quiz-header-right { grid-area: theme;  justify-content: flex-end; }

  .timer-display { font-size: 11px; padding: 3px 8px; }
  .theme-switcher { width: 28px; height: 28px; font-size: 14px; }

  .quiz-title { font-size: 15px; margin-bottom: 1px; }
  .quiz-subtitle { font-size: 10px; }
  .progress-bar { height: 3px; }

  .question-card { padding: 16px; }
  .question-text { font-size: 15px; }
  .option-label { padding: 10px 14px; }
  .option-text { font-size: 14px; }

  .question-actions { flex-direction: column; gap: 8px; }
  .view-solution-btn, .reset-btn { width: 100%; justify-content: center; }

  .quiz-actions { flex-direction: column; gap: 12px; }
  .submit-btn, .reset-all-btn { width: 100%; }
  .score-display { font-size: 32px; }

  .solution-text img,
  .solution-image { margin-top: 12px; margin-bottom: 12px; }
}