body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0 1rem;
    max-width: 900px;
    margin-left: auto;
    margin-right: auto;
  }
  
  header {
    text-align: center;
    padding: 1rem 0;
    background-color: #0077cc;
    color: white;
    margin-bottom: 1rem;
  }
  
  #subjects {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-bottom: 1rem;
    justify-content: center;
  }
  
  .subject-btn {
    padding: 0.5rem 1rem;
    background-color: #eee;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-weight: bold;
  }
  
  .subject-btn.active {
    background-color: #0077cc;
    color: white;
  }
  
  #content {
    border-top: 1px solid #ccc;
    padding-top: 1rem;
  }
  
  .resource-section {
    margin-bottom: 2rem;
  }
  
  .resource-section h2 {
    margin-bottom: 0.5rem;
  }
  
  .resource-list a {
    display: block;
    margin-bottom: 0.25rem;
    color: #0077cc;
    text-decoration: none;
  }
  
  .resource-list a:hover {
    text-decoration: underline;
  }
  
  iframe {
    width: 100%;
    max-width: 560px;
    height: 315px;
    border: none;
    margin-top: 0.5rem;
  }