body {
  font-family: sans-serif;
  background-color: #121212;
  color: #f8f8f8;
  text-align: center;
  padding: 2em;
}

header {
  background-color: #2ecc71;
  color: #fff;
  padding: 2em;
  border-radius: 1em;
}

.btn {
  display: inline-block;
  padding: 1em 2em;
  background-color: #27ae60;
  color: white;
  text-decoration: none;
  border-radius: 0.5em;
}

section {
  margin-top: 3em;
}