body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
  background-image: url("Segelflugplatz.jpg");
  background-size: cover;
  background-position: center;
}
nav ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
}nav li {
  margin: 0 20px;
}nav a {
  color: #fff;
  text-decoration: none;
}main {
  padding: 20px;
}.content-container {
  display: flex;
  justify-content: center;
  align-items: center;
  margin-top: 20px;
  color: green;
}.content-box {
  background-color: rgba(255, 255, 255, 0.8);
  padding: 20px;
  border-radius: 5px;
  flex: 1;
  margin: 0 10px;
  text-align: center;
  width: 300px;
  max-width: 400px;
}