* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Helvetica Neue', Arial, sans-serif;
  line-height: 1.8;
  color: #2c3e50;
  background: linear-gradient(135deg, #f5f7fa 0%, #e9ecef 100%);
  min-height: 100vh;
}

nav {
  background: linear-gradient(90deg, #2c3e50 0%, #34495e 100%);
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
  position: sticky;
  top: 0;
  z-index: 100;
}

nav ul {
  display: flex;
  flex-wrap: nowrap;
  justify-content: space-between;
  align-items: center;
  list-style: none;
  margin: 0;
  padding: 0;
  max-width: 1400px;
  margin: 0 auto;
}

nav li {
  flex: 1 1 0;
  min-width: 0;
  text-align: center;
}

nav a {
  display: block;
  color: #ecf0f1;
  text-decoration: none;
  padding: 16px 12px;
  font-weight: 500;
  transition: all 0.3s ease;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

nav a:hover {
  background: rgba(52, 152, 219, 0.2);
  transform: translateY(-1px);
}

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

header {
  text-align: center;
  margin-bottom: 40px;
  padding: 20px;
  background: white;
  border-radius: 12px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
}

h1 {
  color: #2c3e50;
  font-size: 2em;
  margin-bottom: 15px;
  font-weight: 700;
  line-height: 1.3;
}

h2 {
  color: #34495e;
  font-size: 1.6em;
  margin-top: 30px;
  margin-bottom: 20px;
  padding-bottom: 10px;
  border-bottom: 3px solid #3498db;
  font-weight: 600;
}

section {
  background: white;
  padding: 25px;
  margin-bottom: 25px;
  border-radius: 12px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.06);
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}

section:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 16px rgba(0,0,0,0.1);
}

.intro p {
  font-size: 1.05em;
  line-height: 1.9;
  color: #555;
  text-align: justify;
}

.video-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.video-list li {
  padding: 15px;
  margin-bottom: 12px;
  background: #f8f9fa;
  border-left: 4px solid #3498db;
  border-radius: 6px;
  transition: all 0.3s ease;
}

.video-list li:hover {
  background: #e3f2fd;
  border-left-color: #2980b9;
  transform: translateX(5px);
}

.video-list a {
  color: #2c3e50;
  text-decoration: none;
  font-weight: 600;
  font-size: 1.05em;
}

.video-list a:hover {
  color: #3498db;
  text-decoration: underline;
}

.info-item {
  margin: 12px 0;
  padding: 8px 0;
  border-bottom: 1px solid #ecf0f1;
  font-size: 1.05em;
}

.info-item strong {
  display: inline-block;
  width: 90px;
  color: #34495e;
  font-weight: 600;
}

.ranking li {
  position: relative;
  padding-left: 50px;
}

.rank {
  position: absolute;
  left: 15px;
  top: 15px;
  font-weight: bold;
  color: #3498db;
  font-size: 0.9em;
}

.topic-group {
  margin-bottom: 35px;
}

.latest .date {
  display: inline-block;
  background: #3498db;
  color: white;
  padding: 3px 10px;
  border-radius: 4px;
  font-size: 0.9em;
  font-weight: 600;
  margin-right: 10px;
}

@media (max-width: 768px) {
  nav a {
    padding: 12px 6px;
    font-size: 13px;
  }

  .container {
    padding: 20px 15px;
  }

  h1 {
    font-size: 1.5em;
  }

  h2 {
    font-size: 1.3em;
  }

  section {
    padding: 18px;
  }

  .info-item strong {
    width: 70px;
    font-size: 0.95em;
  }
}

@media (max-width: 480px) {
  nav a {
    padding: 10px 4px;
    font-size: 12px;
  }

  h1 {
    font-size: 1.3em;
  }

  .video-list li {
    padding: 12px;
  }
}