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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: #f5f7fa;
  color: #2d3748;
  line-height: 1.6;
}

header {
  background: linear-gradient(135deg, #1a365d 0%, #2c5282 100%);
  color: white;
  padding: 20px 0;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
}

.header-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 20px;
}

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

.logo-icon {
  font-size: 42px;
}

.logo-text h1 {
  font-size: 28px;
  font-weight: 700;
  margin-bottom: 2px;
}

.logo-text p {
  font-size: 13px;
  opacity: 0.9;
  font-weight: 400;
}

nav {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.nav-link {
  color: white;
  text-decoration: none;
  padding: 10px 18px;
  border-radius: 6px;
  font-weight: 500;
  font-size: 14px;
  transition: all 0.2s;
  background: rgba(255, 255, 255, 0.1);
}

.nav-link:hover {
  background: rgba(255, 255, 255, 0.2);
}

.nav-link.active {
  background: white;
  color: #1a365d;
}

main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 30px 20px;
}

.section {
  background: white;
  border-radius: 12px;
  padding: 28px;
  margin-bottom: 28px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
}

.section-header {
  margin-bottom: 24px;
}

.section-header h2 {
  font-size: 24px;
  color: #1a365d;
  margin-bottom: 6px;
}

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

.video-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
}

.video-card {
  background: #f7fafc;
  border-radius: 10px;
  overflow: hidden;
  transition: transform 0.2s, box-shadow 0.2s;
  cursor: pointer;
}

.video-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 16px rgba(0, 0, 0, 0.12);
}

.video-thumbnail {
  background: linear-gradient(135deg, #4a5568 0%, #2d3748 100%);
  height: 160px;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
}

.video-thumbnail::after {
  content: "▶";
  font-size: 48px;
  color: white;
  opacity: 0.9;
}

.video-info {
  padding: 16px;
}

.video-title {
  font-weight: 600;
  font-size: 16px;
  color: #2d3748;
  margin-bottom: 8px;
}

.video-meta {
  display: flex;
  justify-content: space-between;
  font-size: 13px;
  color: #718096;
}

.video-duration {
  background: #e2e8f0;
  padding: 3px 8px;
  border-radius: 4px;
}

.news-list {
  display: grid;
  gap: 16px;
}

.news-item {
  padding: 20px;
  background: #f7fafc;
  border-left: 4px solid #4299e1;
  border-radius: 8px;
  transition: transform 0.2s;
}

.news-item:hover {
  transform: translateX(4px);
}

.news-date {
  font-size: 13px;
  color: #718096;
  margin-bottom: 8px;
}

.news-title {
  font-weight: 600;
  font-size: 16px;
  color: #2d3748;
  margin-bottom: 8px;
}

.news-excerpt {
  color: #4a5568;
  font-size: 14px;
  line-height: 1.6;
}

.news-tag {
  display: inline-block;
  background: #4299e1;
  color: white;
  padding: 3px 10px;
  border-radius: 12px;
  font-size: 12px;
  margin-top: 10px;
}

.faq-list {
  display: grid;
  gap: 12px;
}

.faq-item {
  border: 1px solid #e2e8f0;
  border-radius: 8px;
  overflow: hidden;
}

.faq-question {
  width: 100%;
  text-align: left;
  padding: 18px 20px;
  background: #f7fafc;
  border: none;
  font-weight: 600;
  font-size: 15px;
  color: #2d3748;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  transition: background 0.2s;
}

.faq-question:hover {
  background: #edf2f7;
}

.faq-question::after {
  content: "+";
  font-size: 24px;
  color: #4a5568;
}

.faq-item.active .faq-question::after {
  content: "−";
}

.faq-answer {
  padding: 0 20px;
  max-height: 0;
  overflow: hidden;
  transition: all 0.3s;
  background: white;
}

.faq-item.active .faq-answer {
  padding: 18px 20px;
  max-height: 500px;
  border-top: 1px solid #e2e8f0;
  color: #4a5568;
  line-height: 1.7;
}

.test-container {
  max-width: 700px;
  margin: 0 auto;
}

.test-start {
  text-align: center;
  padding: 30px 20px;
}

.test-start p {
  font-size: 16px;
  color: #4a5568;
  margin-bottom: 20px;
}

.test-topics {
  list-style: none;
  text-align: left;
  display: inline-block;
  margin-bottom: 30px;
  color: #2d3748;
  font-size: 15px;
  line-height: 2;
}

.test-progress {
  background: #e2e8f0;
  padding: 12px 16px;
  border-radius: 8px;
  margin-bottom: 20px;
  font-weight: 600;
  color: #4a5568;
}

.question-text {
  font-size: 18px;
  font-weight: 600;
  color: #2d3748;
  margin-bottom: 24px;
  line-height: 1.5;
}

.test-options {
  display: grid;
  gap: 12px;
  margin-bottom: 20px;
}

.test-option {
  padding: 16px 20px;
  background: #f7fafc;
  border: 2px solid #e2e8f0;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
  font-size: 15px;
  text-align: left;
}

.test-option:hover {
  border-color: #4299e1;
  background: #ebf8ff;
}

.test-option.correct {
  background: #c6f6d5;
  border-color: #48bb78;
  color: #22543d;
}

.test-option.wrong {
  background: #fed7d7;
  border-color: #f56565;
  color: #742a2a;
}

.test-feedback {
  font-weight: 600;
  font-size: 16px;
  min-height: 24px;
  margin-bottom: 20px;
}

.test-result {
  text-align: center;
  padding: 40px 20px;
}

.result-icon {
  font-size: 72px;
  margin-bottom: 20px;
}

.result-stats {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 20px;
  margin: 30px 0;
}

.result-stat {
  background: #f7fafc;
  padding: 24px;
  border-radius: 10px;
}

.result-value {
  display: block;
  font-size: 42px;
  font-weight: 700;
  color: #4299e1;
  margin-bottom: 8px;
}

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

.result-message {
  font-size: 16px;
  color: #4a5568;
  margin-bottom: 30px;
  line-height: 1.6;
}

.btn-primary {
  background: linear-gradient(135deg, #4299e1 0%, #3182ce 100%);
  color: white;
  border: none;
  padding: 14px 40px;
  border-radius: 8px;
  font-size: 16px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s;
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(66, 153, 225, 0.4);
}

.btn-secondary {
  background: #fc8181;
  color: white;
  border: none;
  padding: 12px 28px;
  border-radius: 8px;
  font-size: 14px;
  font-weight: 500;
  cursor: pointer;
  margin-top: 20px;
  transition: background 0.2s;
}

.btn-secondary:hover {
  background: #f56565;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 20px;
  margin-bottom: 20px;
}

.stat-card {
  background: #f7fafc;
  padding: 24px;
  border-radius: 10px;
  text-align: center;
}

.stat-icon {
  font-size: 32px;
  display: block;
  margin-bottom: 12px;
}

.stat-value {
  display: block;
  font-size: 32px;
  font-weight: 700;
  color: #4299e1;
  margin-bottom: 6px;
}

.stat-label {
  color: #718096;
  font-size: 13px;
}

footer {
  background: #1a365d;
  color: white;
  padding: 30px 20px;
  text-align: center;
}

.footer-content p {
  margin-bottom: 6px;
  font-size: 14px;
}

.footer-note {
  opacity: 0.8;
  font-size: 13px;
}

@media (max-width: 768px) {
  .header-content {
    flex-direction: column;
    text-align: center;
  }
  
  .logo {
    justify-content: center;
  }
  
  nav {
    justify-content: center;
  }
  
  .nav-link {
    padding: 8px 14px;
    font-size: 13px;
  }
  
  .section {
    padding: 20px 16px;
  }
  
  .video-grid {
    grid-template-columns: 1fr;
  }
  
  .result-stats {
    grid-template-columns: 1fr;
  }
}