body {
  font-family: sans-serif;
  margin: 0;
  background: #fafafa;
  color: #222;
}
header {
  background: #111;
  color: #fff;
  padding: 1rem;
  display: flex;
  justify-content: space-between;
}
nav a {
  color: #fff;
  margin-left: 1rem;
  text-decoration: none;
}
main {
  padding: 2rem;
}
canvas {
  max-width: 600px;
  margin: 2rem auto;
  display: block;
}