/* Reset & Base */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg: #0f0f1a;
  --bg-card: #1a1a2e;
  --bg-hover: #252542;
  --text: #e8e8f0;
  --text-muted: #8888a0;
  --primary: #6c5ce7;
  --primary-hover: #7d6ff0;
  --success: #00b894;
  --error: #e74c3c;
  --warning: #fdcb6e;
  --border: #2d2d4a;
  --radius: 12px;
  --shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
}

body {
  font-family:
    "Segoe UI",
    system-ui,
    -apple-system,
    sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.6;
}

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 20px;
  display: grid;
  grid-template-rows: auto auto 1fr auto;
  gap: 20px;
  min-height: 100vh;
}

/* Header */
.header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 15px 20px;
  background: var(--bg-card);
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.header h1 {
  font-size: 1.5rem;
  font-weight: 700;
}

.stats {
  display: flex;
  gap: 20px;
}

.stat {
  font-size: 0.95rem;
  color: var(--text-muted);
}

.stat strong {
  color: var(--text);
}

/* Topic Bar */
.topic-bar {
  display: flex;
  gap: 10px;
}

.topic-bar input {
  flex: 1;
  padding: 12px 16px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-card);
  color: var(--text);
  font-size: 1rem;
  outline: none;
  transition: border-color 0.2s;
}

.topic-bar input:focus {
  border-color: var(--primary);
}

/* Buttons */
.btn {
  padding: 12px 24px;
  border: none;
  border-radius: var(--radius);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}

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

.btn-primary:hover {
  background: var(--primary-hover);
  transform: translateY(-1px);
}

.btn-primary:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

.btn-secondary {
  background: var(--bg-hover);
  color: var(--text);
  border: 1px solid var(--border);
}

.btn-secondary:hover {
  background: var(--border);
}

.btn-small {
  padding: 6px 12px;
  font-size: 0.85rem;
  background: transparent;
  color: var(--text-muted);
  border: 1px solid var(--border);
}

.btn-small:hover {
  background: var(--bg-hover);
  color: var(--text);
}

/* Main Area */
.main {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: 20px;
}

/* Questions Feed */
.questions-feed {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

/* Welcome */
.welcome {
  text-align: center;
  padding: 60px 20px;
  background: var(--bg-card);
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.welcome h2 {
  font-size: 1.8rem;
  margin-bottom: 15px;
}

.welcome p {
  color: var(--text-muted);
  margin-bottom: 10px;
}

.welcome .hint {
  font-size: 0.85rem;
  margin-top: 20px;
}

/* Loading */
.loading {
  text-align: center;
  padding: 40px 20px;
  background: var(--bg-card);
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--border);
  border-top-color: var(--primary);
  border-radius: 50%;
  margin: 0 auto 15px;
  animation: spin 1s linear infinite;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

/* Error */
.error {
  text-align: center;
  padding: 40px 20px;
  background: var(--bg-card);
  border-radius: var(--radius);
  border: 1px solid var(--error);
}

.error p {
  color: var(--error);
  margin-bottom: 20px;
}

/* Question Card */
.question-card {
  background: var(--bg-card);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  padding: 30px;
  box-shadow: var(--shadow);
}

.question-header {
  margin-bottom: 20px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 10px;
}

.question-number {
  font-size: 0.9rem;
  color: var(--text-muted);
  background: var(--bg);
  padding: 6px 12px;
  border-radius: 20px;
}

/* Difficulty Badge */
.difficulty-badge {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 4px 10px;
  border-radius: 12px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.difficulty-badge.easy {
  background: rgba(0, 184, 148, 0.2);
  color: var(--success);
}

.difficulty-badge.medium {
  background: rgba(253, 203, 110, 0.2);
  color: var(--warning);
}

.difficulty-badge.hard {
  background: rgba(231, 76, 60, 0.2);
  color: var(--error);
}

.question-text {
  font-size: 1.25rem;
  font-weight: 500;
  margin-bottom: 25px;
  line-height: 1.5;
}

/* Choices */
.choices {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.choice {
  display: flex;
  align-items: center;
  padding: 16px 20px;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  cursor: pointer;
  transition: all 0.2s;
}

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

.choice.selected {
  border-color: var(--primary);
  background: rgba(108, 92, 231, 0.1);
}

.choice.correct {
  border-color: var(--success);
  background: rgba(0, 184, 148, 0.1);
}

.choice.incorrect {
  border-color: var(--error);
  background: rgba(231, 76, 60, 0.1);
}

.choice.disabled {
  cursor: default;
  opacity: 0.7;
}

.choice-letter {
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-hover);
  border-radius: 8px;
  font-weight: 700;
  margin-right: 15px;
  flex-shrink: 0;
}

.choice.correct .choice-letter {
  background: var(--success);
  color: white;
}

.choice.incorrect .choice-letter {
  background: var(--error);
  color: white;
}

.choice-text {
  flex: 1;
}

/* Feedback */
.feedback {
  margin-top: 25px;
  padding-top: 25px;
  border-top: 1px solid var(--border);
}

.feedback-result {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 15px;
  padding: 12px 16px;
  border-radius: var(--radius);
}

.feedback-result.correct {
  background: rgba(0, 184, 148, 0.15);
  color: var(--success);
}

.feedback-result.incorrect {
  background: rgba(231, 76, 60, 0.15);
  color: var(--error);
}

.explanation {
  color: var(--text-muted);
  margin-bottom: 20px;
  padding: 15px;
  background: var(--bg);
  border-radius: var(--radius);
  font-size: 0.95rem;
}

/* History Panel */
.history-panel {
  background: var(--bg-card);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  padding: 20px;
  max-height: 300px;
  overflow-y: auto;
}

.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 15px;
}

.history-header h3 {
  font-size: 1rem;
}

.history-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.empty-history {
  color: var(--text-muted);
  text-align: center;
  font-size: 0.9rem;
}

.history-item {
  padding: 12px;
  background: var(--bg);
  border-radius: 8px;
  font-size: 0.9rem;
  border-left: 3px solid var(--border);
}

.history-item.correct {
  border-left-color: var(--success);
}

.history-item.incorrect {
  border-left-color: var(--error);
}

.history-item-question {
  font-weight: 500;
  margin-bottom: 5px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.history-item-result {
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* Utility */
.hidden {
  display: none !important;
}

/* Responsive */
@media (max-width: 600px) {
  .container {
    padding: 10px;
  }

  .header {
    flex-direction: column;
    gap: 10px;
    text-align: center;
  }

  .topic-bar {
    flex-direction: column;
  }

  .question-card {
    padding: 20px;
  }

  .question-text {
    font-size: 1.1rem;
  }

  .seo-content {
    padding: 15px;
  }
}

/* Print Styles */
@media print {
  .topic-bar,
  .stats,
  .loading,
  .btn {
    display: none !important;
  }

  body {
    background: white;
    color: black;
  }

  .container {
    max-width: 100%;
  }

  .question-card {
    page-break-inside: avoid;
    border: 1px solid #ccc;
  }
}

/* Accessibility - Skip Link */
.skip-link {
  position: absolute;
  top: -100px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--primary);
  color: white;
  padding: 12px 24px;
  border-radius: var(--radius);
  text-decoration: none;
  font-weight: 600;
  z-index: 1000;
  transition: top 0.3s;
}

.skip-link:focus {
  top: 10px;
}

/* Visually Hidden (for screen readers) */
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Focus Styles for Accessibility */
*:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
}

.btn:focus-visible,
.choice:focus-visible {
  outline: 3px solid var(--primary);
  outline-offset: 3px;
}

/* High Contrast Mode Support */
@media (prefers-contrast: high) {
  :root {
    --bg: #000;
    --bg-card: #111;
    --text: #fff;
    --border: #666;
  }

  .choice {
    border-width: 3px;
  }
}

/* Reduced Motion Support */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  .spinner {
    animation: none;
    border-top-color: var(--primary);
    opacity: 0.5;
  }
}

/* Dark/Light mode preference (already dark, add light alternative) */
@media (prefers-color-scheme: light) {
  :root {
    --bg: #f5f6fa;
    --bg-card: #ffffff;
    --bg-hover: #f0f1f5;
    --text: #1a1a2e;
    --text-muted: #666680;
    --border: #dddde8;
    --shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
  }
}

/* Footer Styles */
.footer {
  padding: 20px;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.85rem;
  border-top: 1px solid var(--border);
  margin-top: auto;
}

.footer a {
  color: var(--primary);
  text-decoration: none;
}

.footer a:hover {
  text-decoration: underline;
}

.footer nav {
  margin-top: 10px;
}

/* SEO Content Section */
.seo-content {
  margin-top: 30px;
  padding: 25px;
  background: var(--bg);
  border-radius: var(--radius);
  text-align: left;
}

.seo-content h3 {
  font-size: 1.1rem;
  margin-bottom: 15px;
  color: var(--text);
}

.seo-content ul {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.seo-content li {
  padding-left: 24px;
  position: relative;
  color: var(--text-muted);
  font-size: 0.95rem;
}

.seo-content li::before {
  content: "✓";
  position: absolute;
  left: 0;
  color: var(--success);
  font-weight: bold;
}

.seo-content li strong {
  color: var(--text);
}

/* Welcome link styles */
.welcome a {
  color: var(--primary);
  text-decoration: none;
}

.welcome a:hover {
  text-decoration: underline;
}

/* Performance: Content visibility for long feeds */
.questions-feed .question-card:nth-child(n + 10) {
  content-visibility: auto;
  contain-intrinsic-size: 0 400px;
}

/* Smooth scroll behavior */
html {
  scroll-behavior: smooth;
}

/* Selection styles */
::selection {
  background: var(--primary);
  color: white;
}

::-moz-selection {
  background: var(--primary);
  color: white;
}

/* Additional difficulty badge levels */
.difficulty-badge.beginner {
  background: rgba(116, 185, 255, 0.2);
  color: #74b9ff;
}

.difficulty-badge.intermediate {
  background: rgba(255, 159, 67, 0.2);
  color: #ff9f43;
}

.difficulty-badge.advanced {
  background: rgba(255, 107, 107, 0.2);
  color: #ff6b6b;
}

.difficulty-badge.expert {
  background: rgba(162, 155, 254, 0.2);
  color: #a29bfe;
}

.difficulty-badge.master {
  background: rgba(253, 121, 168, 0.2);
  color: #fd79a8;
}