body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

header {
  background-color: #333;
  color: #fff;
  padding: 1em;
  text-align: center;
}

nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: space-between;
}

nav li {
  margin-right: 20px;
}

nav button {
  background-color: #333;