* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: #f5f5f5;
  color: #333;
  line-height: 1.5;
}
.container { max-width: 480px; margin: 0 auto; padding: 16px; }
.card {
  background: #fff;
  border-radius: 12px;
  padding: 16px;
  margin-bottom: 12px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.04);
}
.btn {
  display: inline-block;
  width: 100%;
  padding: 12px;
  background: #2a9d8f;
  color: #fff;
  border: none;
  border-radius: 8px;
  font-size: 16px;
  text-align: center;
  cursor: pointer;
}
.btn:disabled { background: #999; }
.btn-sm {
  width: auto;
  padding: 8px 12px;
  font-size: 14px;
}
.input {
  width: 100%;
  padding: 12px;
  border: 1px solid #ddd;
  border-radius: 8px;
  font-size: 16px;
  margin-bottom: 12px;
}
.title { font-size: 20px; font-weight: 600; margin-bottom: 8px; }
.subtitle { font-size: 14px; color: #666; margin-bottom: 12px; }
.course-item {
  display: flex;
  gap: 12px;
  padding: 12px 0;
  border-bottom: 1px solid #f0f0f0;
  cursor: pointer;
}
.course-item:last-child { border-bottom: none; }
.course-cover {
  width: 100px;
  height: 75px;
  background: #e0e0e0;
  border-radius: 8px;
  object-fit: cover;
}
.course-info { flex: 1; }
.course-title { font-size: 16px; font-weight: 500; }
.course-meta { font-size: 13px; color: #888; margin-top: 4px; }
.video-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 12px 0;
  border-bottom: 1px solid #f0f0f0;
}
.video-title { font-size: 15px; }
.video-duration { font-size: 13px; color: #888; }
.player {
  width: 100%;
  border-radius: 8px;
  background: #000;
}
.nav {
  display: flex;
  gap: 12px;
  margin-bottom: 16px;
}
.nav a {
  color: #666;
  text-decoration: none;
  font-size: 15px;
}
.nav a.active { color: #2a9d8f; font-weight: 500; }
.toast {
  position: fixed;
  top: 20px;
  left: 50%;
  transform: translateX(-50%);
  background: rgba(0,0,0,0.8);
  color: #fff;
  padding: 10px 20px;
  border-radius: 20px;
  z-index: 1000;
}