body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
  background-color: #f5f5f5;
}

header {
  background-color: #333;
  color: white;
  padding: 20px;
  text-align: center;
}

h1 {
  margin: 0;
}

main {
  padding: 20px;
}

section h2 {
  border-bottom: 2px solid #333;
  padding-bottom: 10px;
  margin-bottom: 20px;
}

.lecture {
  background-color: white;
  border: 1px solid #ddd;
  border-radius: 5px;
  margin-bottom: 10px;
  padding: 15px;
  cursor: pointer;
}

.lecture h3 {
  margin: 0;
  font-size: 18px;
}

.content {
  display: none;
  margin-top: 10px;
}

.content iframe {
  width: 100%;
  height: 400px;
  border: none;
}

footer {
  background-color: #333;
  color: white;
  text-align: center;
  padding: 10px;
}