body {
  margin: 0;
  font-family: sans-serif;
  color: #333;
  background-color: #fff;
}
header {
  padding: 20px;
  background-color: #000;
  color: #fff;
  text-align: center;
}
nav ul {
  list-style: none;
  padding: 0;
}
nav ul li {
  display: inline-block;
  margin: 0 10px;
}
nav ul li a, nav ul li button {
  color: #fff;
  text-decoration: none;
  font-weight: bold;
  background: none;
  border: none;
  cursor: pointer;
}
section {
  padding: 40px;
}
#subtitle {
  text-align: center;
  white-space: nowrap;
}
footer {
  text-align: center;
  padding: 20px;
  background-color: #000;
  width: 100%;
}