:root {
  --primary-color: #2d5a7b;
  --secondary-color: #4a7ba7;
  --accent-color: #f39c12;
  --text-color: #2c3e50;
  --bg-color: #f8f9fa;
  --card-bg: #ffffff;
  --border-color: #e1e8ed;
  --hover-color: #ecf0f1;
  --shadow: 0 2px 8px rgba(0,0,0,0.08);
  --shadow-hover: 0 4px 16px rgba(0,0,0,0.12);
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Helvetica Neue', Arial, sans-serif;
  line-height: 1.6;
  color: var(--text-color);
  background-color: var(--bg-color);
}

header {
  background-color: var(--card-bg);
  border-bottom: 1px solid var(--border-color);
  box-shadow: var(--shadow);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1rem 1.5rem;
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
  text-decoration: none;
  display: inline-block;
  margin-bottom: 0.5rem;
}

nav ul {
  list-style: none;
  display: flex;
  flex-wrap: nowrap;
  justify-content: flex-start;
  align-items: center;
  gap: 0.5rem;
}

nav ul li {
  flex: 0 0 auto;
}

nav ul li a {
  text-decoration: none;
  color: var(--text-color);
  padding: 0.5rem 1rem;
  border-radius: 4px;
  transition: all 0.3s ease;
  display: block;
  font-size: 0.95rem;
  white-space: nowrap;
}

nav ul li a:hover {
  background-color: var(--hover-color);
  color: var(--primary-color);
}

main {
  max-width: 1200px;
  margin: 2rem auto;
  padding: 0 1.5rem;
}

h1 {
  font-size: 2rem;
  color: var(--primary-color);
  margin-bottom: 1rem;
  line-height: 1.3;
}

h2 {
  font-size: 1.5rem;
  color: var(--primary-color);
  margin: 2rem 0 1rem;
  line-height: 1.3;
}

h3 {
  font-size: 1.2rem;
  color: var(--text-color);
  margin: 1.5rem 0 0.75rem;
}

p {
  margin-bottom: 1rem;
  line-height: 1.8;
}

section {
  background-color: var(--card-bg);
  border-radius: 8px;
  padding: 2rem;
  margin-bottom: 2rem;
  box-shadow: var(--shadow);
}

.intro-section {
  border-left: 4px solid var(--primary-color);
}

.video-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
  margin-top: 1.5rem;
}

.video-card {
  background-color: var(--card-bg);
  border-radius: 8px;
  padding: 1.5rem;
  box-shadow: var(--shadow);
  transition: all 0.3s ease;
  border: 1px solid var(--border-color);
}

.video-card:hover {
  box-shadow: var(--shadow-hover);
  transform: translateY(-4px);
}

.video-card h3 {
  margin-top: 0;
  margin-bottom: 0.5rem;
  font-size: 1.1rem;
}

.video-card h3 a {
  color: var(--text-color);
  text-decoration: none;
  transition: color 0.3s ease;
}

.video-card h3 a:hover {
  color: var(--primary-color);
}

.video-meta {
  font-size: 0.85rem;
  color: #7f8c8d;
  margin-bottom: 0.75rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.video-meta span {
  background-color: var(--bg-color);
  padding: 0.2rem 0.6rem;
  border-radius: 4px;
}

.video-desc {
  font-size: 0.9rem;
  color: #555;
  line-height: 1.6;
  margin-bottom: 0.75rem;
}

.video-link {
  display: inline-block;
  color: var(--secondary-color);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  transition: color 0.3s ease;
}

.video-link:hover {
  color: var(--primary-color);
  text-decoration: underline;
}

.video-list {
  list-style: none;
}

.video-list li {
  background-color: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: 6px;
  padding: 1.25rem;
  margin-bottom: 1rem;
  transition: all 0.3s ease;
}

.video-list li:hover {
  box-shadow: var(--shadow);
  border-color: var(--primary-color);
}

.detail-header {
  border-bottom: 2px solid var(--primary-color);
  padding-bottom: 1rem;
  margin-bottom: 1.5rem;
}

.info-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0;
}

.info-item {
  padding: 0.75rem;
  background-color: var(--bg-color);
  border-radius: 6px;
}

.info-label {
  font-weight: 600;
  color: var(--primary-color);
  margin-bottom: 0.25rem;
}

.info-value {
  color: var(--text-color);
}

.tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 1rem;
}

.tag {
  background-color: var(--secondary-color);
  color: white;
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-size: 0.85rem;
}

.summary-box {
  background-color: var(--bg-color);
  border-left: 4px solid var(--accent-color);
  padding: 1.5rem;
  border-radius: 4px;
  margin: 1.5rem 0;
}

.review-box {
  background-color: #fffbf0;
  border: 1px solid var(--accent-color);
  padding: 1.5rem;
  border-radius: 6px;
  margin: 1.5rem 0;
}

@media (max-width: 768px) {
  .header-container {
    padding: 0.75rem 1rem;
  }

  .logo {
    font-size: 1.2rem;
    margin-bottom: 0.5rem;
  }

  nav ul {
    gap: 0;
    justify-content: space-between;
    flex-wrap: nowrap;
    overflow-x: visible;
  }

  nav ul li {
    flex: 1 1 0;
    min-width: 0;
  }

  nav ul li a {
    padding: 0.4rem 0.3rem;
    font-size: 0.8rem;
    text-align: center;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
  }

  main {
    padding: 0 1rem;
    margin: 1rem auto;
  }

  h1 {
    font-size: 1.5rem;
  }

  h2 {
    font-size: 1.3rem;
  }

  section {
    padding: 1.25rem;
  }

  .video-grid {
    grid-template-columns: 1fr;
    gap: 1rem;
  }

  .info-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .logo {
    font-size: 1.1rem;
  }

  nav ul li a {
    padding: 0.35rem 0.2rem;
    font-size: 0.75rem;
  }

  h1 {
    font-size: 1.3rem;
  }

  section {
    padding: 1rem;
  }
}