body {
      font-family: 'Segoe UI', sans-serif;
      margin: 0;
      padding: 0;
      background: #f0f8ff;
    }

    nav {
      background-color: #3f51b5;
      color: white;
      padding: 15px;
      text-align: center;
    }

    nav a {
      color: white;
      margin: 0 15px;
      text-decoration: none;
      font-weight: bold;
    }

    nav a:hover {
      text-decoration: underline;
    }
main {
  padding: 20px;
}

:root {
  --bg-color: #ffffff;
  --text-color: #000000;
  
}

[data-theme="dark"] {
  --bg-color: #121212;
  --text-color: #ffffff;
  op

}

body {
  background-color: var(--bg-color);
  color: var(--text-color);
  transition: background-color 0.3s, color 0.3s;
}