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

header {
  background: #0A84FF;
  color: white;
  padding: 20px;
  text-align: center;
}

nav {
  display: flex;
  justify-content: center;
  gap: 10px;
  padding: 15px;
  background: #fff;
  border-bottom: 1px solid #ddd;
}

nav button {
  padding: 10px 20px;
  cursor: pointer;
}

.view {
  padding: 20px;
}

.hidden {
  display: none;
}

.lesson-category {
  background: #fff;
  padding: 15px;
  border: 1px solid #ddd;
  border-radius: 8px;
  margin-bottom: 10px;
  cursor: pointer;
}

.lesson-category:hover {
  background: #f0f8ff;
}