:root {
        --primary-color: #2563eb;
        --primary-hover: #1e40af;
        --light-bg: #f3f4f6;
        --border-color: #e5e7eb;
        --text-color: #111827;
        --text-light: #6b7280;
        --user-msg-bg: #e0f2fe;
        --assistant-msg-bg: #ffffff;
        --background-gradient: linear-gradient(135deg, #f8fafc, #e0f2fe);
        --surface-color: #ffffff;
      }

      body.dark {
        --primary-color: #3b82f6;
        --primary-hover: #60a5fa;
        --light-bg: #1f2937;
        --border-color: #4b5563;
        --text-color: #f9fafb;
        --text-light: #9ca3af;
        --user-msg-bg: #1e3a8a;
        --assistant-msg-bg: #374151;
        --background-gradient: linear-gradient(135deg, #1f2937, #111827);
        --surface-color: #1f2937;
      }

      * {
        box-sizing: border-box;
        margin: 0;
        padding: 0;
      }

      body {
        font-family:
          "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,
          Ubuntu, Cantarell, sans-serif;
        line-height: 1.6;
        color: var(--text-color);
        background: var(--background-gradient);
        min-height: 100vh;
        transition: background 0.3s, color 0.3s;
      }

      main {
        max-width: 800px;
        margin: 0 auto;
        padding: 1rem;
      }

      header {
        text-align: center;
        margin-bottom: 2rem;
        padding: 1rem 0;
        border-bottom: 1px solid var(--border-color);
      }

      header .tagline {
        font-size: 0.95rem;
        color: var(--text-light);
      }

      h1 {
        font-size: 1.5rem;
        color: var(--primary-color);
      }

      .top-nav {
        display: flex;
        justify-content: space-between;
        align-items: center;
        padding: 0.75rem 1rem;
        background: var(--surface-color);
        border-bottom: 1px solid var(--border-color);
        box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
      }

      .nav-title {
        font-weight: 600;
        color: var(--primary-color);
      }

      .theme-toggle {
        font-size: 1.25rem;
        background: none;
        border: none;
        cursor: pointer;
        color: var(--text-color);
        transition: color 0.2s;
      }

      .theme-toggle:hover {
        color: var(--primary-color);
      }

      .chat-container {
        display: flex;
        flex-direction: column;
        min-height: 400px;
        border: 1px solid var(--border-color);
        border-radius: 12px;
        overflow: hidden;
        background: var(--surface-color);
        box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
      }

      @media (min-width: 768px) {
        .chat-container {
          height: calc(100vh - 750px);
        }
      }

      @media (max-width: 767px) {
        body {
          display: flex;
          flex-direction: column;
          min-height: 100vh;
        }
        main {
          flex: 1;
          display: flex;
          flex-direction: column;
        }
        .chat-container {
          flex: 1;
          min-height: auto;
        }
        footer {
          margin-top: auto;
        }
      }

      .chat-messages {
        flex: 1;
        overflow-y: auto;
        padding: 1rem;
        background-color: var(--light-bg);
      }

      .message {
        margin-bottom: 1rem;
        padding: 0.75rem;
        border-radius: 8px;
        max-width: 80%;
        animation: fadeInUp 0.3s ease;
      }

      .user-message {
        background-color: var(--user-msg-bg);
        align-self: flex-end;
        margin-left: auto;
      }

      .assistant-message {
        background-color: var(--assistant-msg-bg);
        align-self: flex-start;
      }

      .message-input {
        display: flex;
        padding: 0.75rem;
        border-top: 1px solid var(--border-color);
        background-color: var(--surface-color);
      }

      #user-input {
        flex: 1;
        padding: 0.75rem;
        border: 1px solid var(--border-color);
        border-radius: 8px;
        font-family: inherit;
        font-size: 16px;
        resize: none;
        min-height: 44px;
        background: var(--surface-color);
        color: var(--text-color);
      }

      #user-input::placeholder {
        color: var(--text-light);
      }

      #send-button {
        margin-left: 0.5rem;
        padding: 0 1.25rem;
        background-color: var(--primary-color);
        color: white;
        border: none;
        border-radius: 8px;
        cursor: pointer;
        font-weight: 500;
        font-size: 16px;
        transition: background-color 0.2s, transform 0.1s;
      }

      #send-button:hover {
        background-color: var(--primary-hover);
        transform: translateY(-1px);
      }

      #send-button:active {
        transform: scale(0.97);
      }

      #send-button:disabled {
        background-color: var(--text-light);
        cursor: not-allowed;
      }

      .typing-indicator {
        display: none;
        margin-bottom: 1rem;
        font-style: italic;
        color: var(--text-light);
      }

      .typing-indicator.visible {
        display: block;
      }

      footer {
        margin-top: 1rem;
        text-align: center;
        font-size: 0.85rem;
        color: var(--text-light);
      }


  .welcome-container {
    background: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 20px;
    max-width: 800px;
    color: var(--text-color);
    line-height: 1.6;
    margin-bottom: 2rem;
    margin-top: 2rem;
  }
  .welcome-inner {
    background: var(--surface-color);
    border: 0;
    border-radius: 0;
    padding: 10px;
    margin-bottom: 0;
    margin-top: 0;
  }


  .welcome-container p {
    margin: 12px 0;
  }

  .welcome-container ul {
    padding-left: 20px;
    margin-top: 8px;
    margin-bottom: 16px;
  }

  .welcome-container li {
    margin-bottom: 6px;
  }

  .welcome-container strong {
    color: var(--text-color);
  }

  .welcome-container em {
    color: var(--text-light);
    font-style: italic;
  }

  .welcome-container small {
    font-size: 0.9em;
    color: var(--text-light);
  }

  .welcome-container u {
    text-decoration: underline;
  }

  @media (max-width: 767px) {
    header p {
      display: none;
    }
    .welcome-container.desktop {
      display: none;
    }
    .collapsible-container {
      display: none;
    }
    .welcome-container.mobile {
      display: block;
    }
    main {
      padding: 0.5rem;
    }
    header {
      margin-bottom: 1rem;
      padding: 0.5rem 0;
    }
    .top-nav {
      padding: 0.5rem;
    }
    .chat-messages {
      padding: 0.5rem;
    }
    .message {
      margin-bottom: 0.5rem;
      padding: 0.5rem;
    }
    .message-input {
      padding: 0.5rem;
    }
    #user-input {
      padding: 0.5rem;
    }
    #send-button {
      margin-left: 0.25rem;
      padding: 0 0.75rem;
    }
    .welcome-container {
      padding: 15px;
      margin-top: 1rem;
      margin-bottom: 1rem;
    }
  }

  @media (min-width: 768px) {
    .welcome-container.mobile {
      display: none;
    }
  }

  .collapsible-container {
      max-width: 800px;
      margin: 20px auto;
    }

    .collapsible-title {
      cursor: pointer;
      background-color: var(--surface-color);
      padding: 12px 16px;
      border: 1px solid var(--border-color);
      border-radius: 6px;
      transition: background-color 0.3s;
      color: var(--text-color);
    }

    .collapsible-title:hover {
      background-color: var(--light-bg);
    }

    .collapsible-content {
      padding: 12px 16px;
      border: 1px solid var(--border-color);
      border-radius: 0 0 6px 6px;
      display: none;
      background: var(--surface-color);
      color: var(--text-color);
    }

    input[type="checkbox"].toggle-box {
      display: none;
    }

    input[type="checkbox"].toggle-box:checked ~ .collapsible-content {
      display: block;
    }

    @keyframes fadeInUp {
      from {
        opacity: 0;
        transform: translateY(4px);
      }
      to {
        opacity: 1;
        transform: translateY(0);
      }
    }