style>
    /* Reset basique */
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    html, body {
      height: 100%;
      font-family: Arial, sans-serif;
    }

    /* Fond global avec image */
    .page-background {
      background: url('https://images.unsplash.com/photo-1506744038136-46273834b3fb?auto=format&fit=crop&w=1470&q=80') no-repeat center center fixed;
      background-size: cover;
      height: 100vh;
      width: 100vw;
      display: flex;
      justify-content: center;
      align-items: center;
      padding: 20px;
    }

    /* Conteneur principal blanc semi-transparent */
    .page-container {
      background-color: rgba(255, 255, 255, 0.9);
      width: 90%;
      height: 90%;
      display: flex;
      border-radius: 15px;
      box-shadow: 0 0 15px rgba(0,0,0,0.3);
      overflow: hidden;
    }

    /* Blocs à l’intérieur */
    .left-sidebar, .main-content, .right-sidebar {
      padding: 20px;
      overflow-y: auto;
      display: flex;
      flex-direction: column;
      justify-content: flex-start;
      align-items: flex-start;
    }

    .left-sidebar {
      width: 20%;
      background-color: rgba(240, 240, 240, 0.9);
      border-right: 1px solid #ccc;
    }

    .main-content {
      flex-grow: 1;
      background-color: rgba(255, 255, 255, 0.95);
      margin: 0 15px;
    }

    .right-sidebar {
      width: 25%;
      background-color: rgba(240, 240, 240, 0.9);
      border-left: 1px solid #ccc;
    }

    /* Simple scrollbar pour la demo */
    .left-sidebar::-webkit-scrollbar,
    .main-content::-webkit-scrollbar,
    .right-sidebar::-webkit-scrollbar {
      width: 6px;
    }

    .left-sidebar::-webkit-scrollbar-thumb,
    .main-content::-webkit-scrollbar-thumb,
    .right-sidebar::-webkit-scrollbar-thumb {
      background-color: rgba(0,0,0,0.2);
      border-radius: 3px;
    }

    /* Titres */
    h2 {
      margin-bottom: 15px;
      color: #333;
    }
  </style>