body { 

      font-family: Arial, sans-serif;
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100vh;
      margin: 0;
      background-color: #f0f0f0;
}
header { background: #333; color: #fff; padding: 1em; }
header h1 { margin: 0; }
nav a { color: #fff; margin-right: 1em; text-decoration: none; }
main { padding: 2em; background: #fff; }
footer { text-align: center; padding: 1em; background: #eee; }
canvas {border: 2px solid black;}