body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    margin: 0;
    padding: 0;
    background: linear-gradient(45deg, #8e44ad, #3498db); 
    display: flex;
    flex-direction: column;
    align-items: center;
    height: 100vh;
    text-align: center;
    color: white;
  }
  
  header nav {
    background-color: rgba(52, 152, 219, 0.8); 
    width: 100%;
    padding: 15px 0;
    position: sticky;
    top: 0;
    z-index: 10;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
  }
  
  header nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
  }
  
  header nav ul li {
    margin: 0 20px;
  }
  
  header nav ul li button {
    padding: 10px 20px;
    background-color: #2980b9;
    color: white;
    border: none;
    font-size: 18px;
    cursor: pointer;
    border-radius: 25px;
    transition: all 0.3s ease;
  }
  
  header nav ul li button:hover {
    background-color: #3498db;
    transform: scale(1.1);
  }
  
  header hr {
    width: 60%;
    border: 1px solid #3498db;
    margin: 20px 0;
  }
  
  #contenu {
    width: 80%;
    max-width: 1200px;
    margin-top: 50px;
  }
  
  .contenu-section {
    display: none;
    margin: 40px 0;
    animation: fadeIn 1s ease-out;
  }
  
  @keyframes fadeIn {
    0% {
      opacity: 0;
      transform: translateY(20px);
    }
    100% {
      opacity: 1;
      transform: translateY(0);
    }
  }
  
  h2 {
    font-size: 28px;
    margin-bottom: 20px;
  }
  
  ul {
    list-style-type: none;
    padding: 0;
  }
  
  ul li {
    font-size: 18px;
    margin-bottom: 10px;
    line-height: 1.6;
  }
  
  ul li strong {
    color: #f39c12;
  }

.back-button {
  position: fixed;
  bottom: 20px;  
  left: 20px; 
  padding: 12px 20px;
  font-size: 18px;
  color: white;
  background-color: #3498db;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  transition: background-color 0.3s ease;
}

.back-button:hover {
  background-color: #2980b9;
}