body {
      margin: 0;
      font-family: Arial, sans-serif;
      background: #f5f7fb;
      color: #1f2937;
    }

    .app {
      max-width: 720px;
      margin: 0 auto;
      min-height: 100vh;
      display: flex;
      flex-direction: column;
      background: #ffffff;
    }

    header {
      padding: 18px;
      border-bottom: 1px solid #e5e7eb;
      background: #ffffff;
    }

    header h1 {
      font-size: 20px;
      margin: 0 0 6px;
    }

    header p {
      margin: 0;
      font-size: 14px;
      color: #6b7280;
    }

    #messages {
      flex: 1;
      padding: 18px;
      overflow-y: auto;
    }

    .message {
      max-width: 85%;
      padding: 12px 14px;
      margin-bottom: 12px;
      border-radius: 14px;
      line-height: 1.4;
      white-space: pre-wrap;
    }

    .guest {
      margin-left: auto;
      background: #2563eb;
      color: white;
      border-bottom-right-radius: 4px;
    }

    .assistant {
      margin-right: auto;
      background: #f3f4f6;
      color: #111827;
      border-bottom-left-radius: 4px;
    }

    .system {
      margin: 12px auto;
      background: #fff7ed;
      color: #9a3412;
      font-size: 14px;
      text-align: center;
    }

    form {
      display: flex;
      gap: 8px;
      padding: 14px;
      border-top: 1px solid #e5e7eb;
      background: #ffffff;
    }

    input {
      flex: 1;
      padding: 12px;
      border: 1px solid #d1d5db;
      border-radius: 10px;
      font-size: 16px;
    }

    button {
      padding: 12px 16px;
      border: 0;
      border-radius: 10px;
      background: #2563eb;
      color: white;
      font-size: 16px;
      cursor: pointer;
    }

    button:disabled {
      background: #9ca3af;
      cursor: not-allowed;
    }

    .small {
      font-size: 13px;
      color: #6b7280;
      margin-top: 6px;
    }