body {
  background-color: #fff;
  color: black;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}

a:link,
a:active {
  text-decoration: none;
}

@media (max-width: 640px) {
  .header {
    text-align: center;
  }
}