body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  margin: 0;
  padding: 0;
  background: #f6f8fa;
  color: #24292e;
}
header {
  background: #0366d6;
  color: white;
  padding: 20px;
  text-align: center;
}
nav {
  background: #eaecef;
  padding: 10px 20px;
}
nav a {
  color: #0366d6;
  text-decoration: none;
  font-weight: bold;
}
main {
  padding: 20px;
}
section {
  background: white;
  padding: 20px;
  margin-bottom: 20px;
  border-radius: 6px;
  box-shadow: 0 1px 3px rgba(27,31,35,0.12);
}
footer {
  background: #24292e;
  color: white;
  text-align: center;
  padding: 10px;
}