body {
    margin: 0;
    font-family: Arial, sans-serif;
    background: #f5f5f5;
    color: #333;
    scroll-behavior: smooth;
    transition: background 0.3s, color 0.3s;
  }
  
  header {
    background: #4CAF50;
    color: white;
    padding: 1rem;
    position: sticky;
    top: 0;
    z-index: 1000;
  }
  
  nav {
    display: flex;
    justify-content: center;
    gap: 1.5rem;
  }
  
  nav a {
    color: white;
    text-decoration: none;
    font-weight: bold;
    position: relative;
  }
  
  nav a.active::after {
    content: '';
    position: absolute;
    bottom: -5px;
    left: 0;
    height: 2px;
    width: 100%;
    background: white;
  }
  
  .container {
    padding: 2rem;
    max-width: 900px;
    margin: auto;
  }
  
  .card {
    background: white;
    padding: 1.5rem;
    border-radius: 15px;
    box-shadow: 5px 5px 15px #ddd, -5px -5px 15px #fff;
    margin: 1.5rem 0;
    transition: transform 0.3s ease, box-shadow 0.3s ease;
  }
  
  .card:hover {
    transform: scale(1.02);
    box-shadow: 0 8px 20px #bbb;
  }
  
  button {
    background: #4CAF50;
    color: white;
    border: none;
    padding: 0.6rem 1.2rem;
    margin-top: 1rem;
    border-radius: 8px;
    cursor: pointer;
    transition: background 0.3s;
  }
  
  button:hover {
    background: #45a049;
  }
  
  #scrollTop {
    position: fixed;
    bottom: 20px;
    right: 20px;
    background: #4CAF50;
    color: white;
    padding: 0.7rem;
    border-radius: 50%;
    cursor: pointer;
    display: none;
    z-index: 999;
    border: none;
    box-shadow: 0 4px 8px rgba(0,0,0,0.2);
  }
  
  .dark-mode {
    background: #121212;
    color: #eee;
  }
  
  .dark-mode .card {
    background: #1f1f1f;
    color: #eee;
    box-shadow: 5px 5px 15px #0e0e0e, -5px -5px 15px #1c1c1c;
  }
  
  .dark-mode header {
    background: #2e7d32;
  }
  
  .dark-mode button,
  .dark-mode #scrollTop {
    background: #2e7d32;
  }
  
  .dark-toggle {
    position: fixed;
    top: 1rem;
    right: 1rem;
    display: flex;
    align-items: center;
    font-size: 0.9rem;
    gap: 0.5rem;
    background: #fff;
    padding: 0.4rem 0.8rem;
    border-radius: 20px;
    box-shadow: 0 0 5px #ccc;
  }
  
  .dark-mode .dark-toggle {
    background: #2a2a2a;
    color: #eee;
    box-shadow: 0 0 5px #000;
  }
  
  input[type="checkbox"] {
    accent-color: #4CAF50;
    width: 20px;
    height: 20px;
  }
  
  form {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    max-width: 500px;
    margin: 2rem auto;
  }
  
  form input, form textarea {
    padding: 0.8rem;
    border-radius: 8px;
    border: 1px solid #ccc;
    font-size: 1rem;
    width: 100%;
  }
  
  form input:focus, form textarea:focus {
    outline: none;
    border-color: #4CAF50;
  }
  
  @media (max-width: 600px) {
    nav {
      flex-direction: column;
      align-items: center;
    }
  
    .dark-toggle {
      top: auto;
      bottom: 1rem;
    }
  }