/* Modern UI with professional styling */
    @import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');
    
    :root {
      /* Dark theme colors */
      --primary-bg: #1a1a1a;
      --secondary-bg: #2d2d2d;
      --tertiary-bg: #3d3d3d;
      --primary-text: #ffffff;
      --secondary-text: #b3b3b3;
      --accent-color: #4d8bf0;
      --accent-hover: #3a7bd5;
      --success-color: #28a745;
      --error-color: #dc3545;
      --warning-color: #ffc107;
      --border-radius: 12px;
      --box-shadow: 0 4px 20px rgba(0, 0, 0, 0.15);
      --transition: all 0.3s ease;
    }
    
    .light-theme {
      /* Light theme colors */
      --primary-bg: #ffffff;
      --secondary-bg: #f5f5f5;
      --tertiary-bg: #e9e9e9;
      --primary-text: #333333;
      --secondary-text: #666666;
      --accent-color: #4d8bf0;
      --accent-hover: #3a7bd5;
    }
    
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
      font-family: 'Inter', sans-serif;
    }
    
    body {
      background-color: var(--primary-bg);
      color: var(--primary-text);
      transition: var(--transition);
      min-height: 100vh;
      display: flex;
      flex-direction: column;
    }
    
    /* Header styles */
    .header {
      padding: 1.5rem 2rem;
      background-color: var(--secondary-bg);
      border-bottom: 1px solid rgba(255, 255, 255, 0.1);
      display: flex;
      justify-content: space-between;
      align-items: center;
      position: relative;
      z-index: 10;
    }
    
    .logo-container {
      display: flex;
      align-items: center;
      gap: 1rem;
    }
    
    .logo {
      width: 40px;
      height: 40px;
      border-radius: 50%;
      object-fit: cover;
    }
    
    .logo-text {
      font-size: 1.5rem;
      font-weight: 600;
      background: linear-gradient(90deg, #4d8bf0, #6e45e2);
      -webkit-background-clip: text;
      -webkit-text-fill-color: transparent;
    }
    
    .nav-controls {
      display: flex;
      gap: 1rem;
      align-items: center;
    }
    
    .control-btn {
      background-color: var(--tertiary-bg);
      border: none;
      width: 40px;
      height: 40px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      color: var(--primary-text);
      transition: var(--transition);
    }
    
    .control-btn:hover {
      background-color: var(--accent-color);
      color: white;
    }
    
    /* Main content area */
    .main-container {
      display: flex;
      flex: 1;
      overflow: hidden;
    }
    
    .sidebar {
      width: 280px;
      background-color: var(--secondary-bg);
      border-right: 1px solid rgba(255, 255, 255, 0.1);
      padding: 1.5rem;
      display: flex;
      flex-direction: column;
      transition: var(--transition);
      overflow-y: auto;
    }
    
    .sidebar-collapsed {
      width: 80px;
    }
    
    .sidebar-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 1.5rem;
    }
    
    .sidebar-title {
      font-size: 1.1rem;
      font-weight: 600;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }
    
    .collapse-btn {
      background: none;
      border: none;
      color: var(--secondary-text);
      cursor: pointer;
      font-size: 1.2rem;
    }
    
    .chat-history {
      flex: 1;
      overflow-y: auto;
    }
    
    .chat-item {
      padding: 0.8rem;
      border-radius: var(--border-radius);
      margin-bottom: 0.5rem;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 0.8rem;
      transition: var(--transition);
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }
    
    .chat-item:hover {
      background-color: var(--tertiary-bg);
    }
    
    .chat-item.active {
      background-color: var(--accent-color);
      color: white;
    }
    
    .chat-item-icon {
      min-width: 20px;
    }
    
    .chat-item-text {
      overflow: hidden;
      text-overflow: ellipsis;
    }
    
    .new-chat-btn {
      width: 100%;
      padding: 0.8rem;
      border-radius: var(--border-radius);
      background-color: var(--accent-color);
      color: white;
      border: none;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 0.5rem;
      cursor: pointer;
      margin-top: 1rem;
      transition: var(--transition);
    }
    
    .new-chat-btn:hover {
      background-color: var(--accent-hover);
    }
    
    /* Chat area */
    .chat-container {
      flex: 1;
      display: flex;
      flex-direction: column;
      overflow: hidden;
    }
    
    .chat-messages {
      flex: 1;
      padding: 2rem;
      overflow-y: auto;
      background-color: var(--primary-bg);
    }
    
    .message {
      display: flex;
      gap: 1.2rem;
      margin-bottom: 1.8rem;
      max-width: 800px;
      margin-left: auto;
      margin-right: auto;
    }
    
    .message-avatar {
      width: 40px;
      height: 40px;
      border-radius: 50%;
      object-fit: cover;
      flex-shrink: 0;
      background-color: var(--tertiary-bg);
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 1.2rem;
    }
    
    .message-content {
      flex: 1;
    }
    
    .message-header {
      display: flex;
      align-items: center;
      margin-bottom: 0.5rem;
      gap: 0.8rem;
    }
    
    .message-sender {
      font-weight: 600;
    }
    
    .message-time {
      font-size: 0.8rem;
      color: var(--secondary-text);
    }
    
    .message-text {
      line-height: 1.6;
      white-space: pre-wrap;
    }
    
    .message-actions {
      display: flex;
      gap: 0.5rem;
      margin-top: 0.8rem;
    }
    
    .action-btn {
      background: none;
      border: none;
      color: var(--secondary-text);
      cursor: pointer;
      font-size: 1rem;
      transition: var(--transition);
      padding: 0.3rem 0.6rem;
      border-radius: 4px;
    }
    
    .action-btn:hover {
      color: var(--accent-color);
      background-color: rgba(77, 139, 240, 0.1);
    }
    
    .incoming-message {
      margin-right: auto;
    }
    
    .outgoing-message {
      margin-left: auto;
      flex-direction: row-reverse;
    }
    
    .outgoing-message .message-content {
      text-align: right;
    }
    
    .outgoing-message .message-header {
      justify-content: flex-end;
    }
    
    .outgoing-message .message-actions {
      justify-content: flex-end;
    }
    
    .typing-indicator {
      display: flex;
      gap: 0.5rem;
      padding: 1rem;
      background-color: var(--secondary-bg);
      border-radius: var(--border-radius);
      margin-bottom: 1.8rem;
      max-width: 800px;
      margin-left: auto;
      margin-right: auto;
    }
    
    .typing-dot {
      width: 8px;
      height: 8px;
      background-color: var(--secondary-text);
      border-radius: 50%;
      animation: typingAnimation 1.4s infinite ease-in-out;
    }
    
    .typing-dot:nth-child(1) {
      animation-delay: 0s;
    }
    
    .typing-dot:nth-child(2) {
      animation-delay: 0.2s;
    }
    
    .typing-dot:nth-child(3) {
      animation-delay: 0.4s;
    }
    
    @keyframes typingAnimation {
      0%, 60%, 100% {
        transform: translateY(0);
      }
      30% {
        transform: translateY(-5px);
      }
    }
    
    /* Input area */
    .input-container {
      padding: 1.5rem;
      background-color: var(--secondary-bg);
      border-top: 1px solid rgba(255, 255, 255, 0.1);
    }
    
    .input-box {
      max-width: 800px;
      margin: 0 auto;
      position: relative;
    }
    
    .input-toolbar {
      display: flex;
      gap: 0.5rem;
      margin-bottom: 0.8rem;
    }
    
    .tool-btn {
      background-color: var(--tertiary-bg);
      border: none;
      width: 36px;
      height: 36px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      color: var(--primary-text);
      transition: var(--transition);
    }
    
    .tool-btn:hover {
      background-color: var(--accent-color);
      color: white;
    }
    
    .input-field {
      width: 100%;
      min-height: 60px;
      max-height: 200px;
      padding: 1rem 5rem 1rem 1.5rem;
      border-radius: var(--border-radius);
      border: none;
      background-color: var(--tertiary-bg);
      color: var(--primary-text);
      resize: none;
      font-size: 1rem;
      line-height: 1.5;
      transition: var(--transition);
    }
    
    .input-field:focus {
      outline: none;
      box-shadow: 0 0 0 2px var(--accent-color);
    }
    
    .input-actions {
      position: absolute;
      right: 1rem;
      bottom: 1rem;
      display: flex;
      gap: 0.5rem;
    }
    
    .send-btn {
      background-color: var(--accent-color);
      color: white;
      border: none;
      width: 40px;
      height: 40px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      transition: var(--transition);
    }
    
    .send-btn:hover {
      background-color: var(--accent-hover);
      transform: scale(1.05);
    }
    
    .disclaimer {
      text-align: center;
      font-size: 0.8rem;
      color: var(--secondary-text);
      margin-top: 1rem;
      padding: 0 2rem;
    }
    
    /* File upload modal */
    .modal {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      background-color: rgba(0, 0, 0, 0.7);
      display: flex;
      align-items: center;
      justify-content: center;
      z-index: 1000;
      opacity: 0;
      visibility: hidden;
      transition: var(--transition);
    }
    
    .modal.active {
      opacity: 1;
      visibility: visible;
    }
    
    .modal-content {
      background-color: var(--secondary-bg);
      border-radius: var(--border-radius);
      width: 90%;
      max-width: 500px;
      padding: 2rem;
      box-shadow: var(--box-shadow);
      transform: translateY(-20px);
      transition: var(--transition);
    }
    
    .modal.active .modal-content {
      transform: translateY(0);
    }
    
    .modal-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 1.5rem;
    }
    
    .modal-title {
      font-size: 1.2rem;
      font-weight: 600;
    }
    
    .close-btn {
      background: none;
      border: none;
      font-size: 1.5rem;
      cursor: pointer;
      color: var(--secondary-text);
    }
    
    .file-drop-area {
      border: 2px dashed var(--secondary-text);
      border-radius: var(--border-radius);
      padding: 2rem;
      text-align: center;
      cursor: pointer;
      transition: var(--transition);
      margin-bottom: 1.5rem;
    }
    
    .file-drop-area:hover {
      border-color: var(--accent-color);
    }
    
    .file-drop-icon {
      font-size: 2.5rem;
      margin-bottom: 1rem;
      color: var(--secondary-text);
    }
    
    .file-drop-text {
      margin-bottom: 0.5rem;
    }
    
    .file-drop-hint {
      font-size: 0.8rem;
      color: var(--secondary-text);
    }
    
    .file-input {
      display: none;
    }
    
    .file-selected {
      display: none;
      margin-top: 1rem;
      padding: 1rem;
      background-color: var(--tertiary-bg);
      border-radius: var(--border-radius);
    }
    
    .file-info {
      display: flex;
      align-items: center;
      gap: 0.8rem;
    }
    
    .file-icon {
      font-size: 1.5rem;
    }
    
    .file-name {
      flex: 1;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }
    
    .remove-file {
      color: var(--error-color);
      cursor: pointer;
    }
    
    .modal-actions {
      display: flex;
      justify-content: flex-end;
      gap: 1rem;
      margin-top: 1.5rem;
    }
    
    .modal-btn {
      padding: 0.7rem 1.5rem;
      border-radius: var(--border-radius);
      cursor: pointer;
      transition: var(--transition);
      font-weight: 500;
    }
    
    .cancel-btn {
      background-color: var(--tertiary-bg);
      border: none;
      color: var(--primary-text);
    }
    
    .cancel-btn:hover {
      background-color: #444;
    }
    
    .upload-btn {
      background-color: var(--accent-color);
      border: none;
      color: white;
    }
    
    .upload-btn:hover {
      background-color: var(--accent-hover);
    }
    
    /* Educational Tools Panel */
    .edu-tools {
      position: fixed;
      bottom: 20px;
      right: 20px;
      z-index: 100;
      display: flex;
      flex-direction: column;
      gap: 15px;
    }
    
    .tool-btn-main {
      background-color: var(--accent-color);
      color: white;
      border: none;
      width: 60px;
      height: 60px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
      transition: var(--transition);
      font-size: 1.5rem;
      position: relative;
    }
    
    .tool-btn-main:hover {
      background-color: var(--accent-hover);
      transform: translateY(-3px);
    }
    
    .tool-btn-main.active {
      background-color: var(--warning-color);
      color: var(--primary-text);
    }
    
    .tool-panel {
      position: absolute;
      bottom: 80px;
      right: 0;
      width: 350px;
      background-color: var(--secondary-bg);
      border-radius: var(--border-radius);
      box-shadow: var(--box-shadow);
      padding: 1.5rem;
      display: none;
    }
    
    .tool-panel.active {
      display: block;
      animation: fadeIn 0.3s ease;
    }
    
    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(10px); }
      to { opacity: 1; transform: translateY(0); }
    }
    
    .tool-title {
      font-size: 1.1rem;
      margin-bottom: 1rem;
      color: var(--accent-color);
      display: flex;
      justify-content: space-between;
      align-items: center;
    }
    
    .tool-close {
      background: none;
      border: none;
      color: var(--secondary-text);
      cursor: pointer;
      font-size: 1.2rem;
    }
    
    .tool-input {
      width: 100%;
      padding: 0.8rem 1rem;
      border-radius: var(--border-radius);
      border: 1px solid var(--tertiary-bg);
      background-color: var(--tertiary-bg);
      color: var(--primary-text);
      margin-bottom: 1rem;
      resize: none;
    }
    
    .tool-select {
      width: 100%;
      padding: 0.8rem;
      border-radius: var(--border-radius);
      border: 1px solid var(--tertiary-bg);
      background-color: var(--tertiary-bg);
      color: var(--primary-text);
      margin-bottom: 1rem;
    }
    
    .tool-submit {
      width: 100%;
      padding: 0.8rem;
      border-radius: var(--border-radius);
      background-color: var(--accent-color);
      color: white;
      border: none;
      cursor: pointer;
      transition: var(--transition);
      font-weight: 500;
    }
    
    .tool-submit:hover {
      background-color: var(--accent-hover);
    }
    
    .tool-options {
      display: flex;
      gap: 0.5rem;
      margin-bottom: 1rem;
    }
    
    .tool-option-btn {
      flex: 1;
      padding: 0.6rem;
      border-radius: var(--border-radius);
      background-color: var(--tertiary-bg);
      border: none;
      color: var(--primary-text);
      cursor: pointer;
      transition: var(--transition);
      text-align: center;
      font-size: 0.9rem;
    }
    
    .tool-option-btn.active {
      background-color: var(--accent-color);
      color: white;
    }
    
    .tool-option-btn:hover:not(.active) {
      background-color: rgba(77, 139, 240, 0.2);
    }
    
    /* Flashcard styles */
    .flashcard {
      width: 100%;
      height: 200px;
      perspective: 1000px;
      margin-bottom: 1rem;
    }
    
    .flashcard-inner {
      position: relative;
      width: 100%;
      height: 100%;
      transition: transform 0.6s;
      transform-style: preserve-3d;
      cursor: pointer;
    }
    
    .flashcard.flipped .flashcard-inner {
      transform: rotateY(180deg);
    }
    
    .flashcard-front, .flashcard-back {
      position: absolute;
      width: 100%;
      height: 100%;
      backface-visibility: hidden;
      border-radius: var(--border-radius);
      padding: 1.5rem;
      display: flex;
      align-items: center;
      justify-content: center;
      text-align: center;
      background-color: var(--tertiary-bg);
      box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
    }
    
    .flashcard-back {
      transform: rotateY(180deg);
      background-color: var(--accent-color);
      color: white;
    }
    
    .flashcard-nav {
      display: flex;
      justify-content: space-between;
      margin-top: 1rem;
    }
    
    .flashcard-count {
      font-size: 0.9rem;
      color: var(--secondary-text);
    }
    
    /* Responsive styles */
    @media (max-width: 992px) {
      .sidebar {
        width: 250px;
      }
    }
    
    @media (max-width: 768px) {
      .sidebar {
        position: fixed;
        top: 0;
        left: -100%;
        height: 100vh;
        z-index: 100;
        transition: var(--transition);
      }
      
      .sidebar.active {
        left: 0;
      }
      
      .sidebar-collapsed {
        left: -100%;
      }
      
      .main-container {
        margin-left: 0;
      }
      
      .message {
        max-width: 100%;
      }
      
      .tool-panel {
        width: 300px;
        right: -10px;
      }
    }
    
    @media (max-width: 576px) {
      .header {
        padding: 1rem;
      }
      
      .logo-text {
        font-size: 1.2rem;
      }
      
      .chat-messages {
        padding: 1rem;
      }
      
      .input-container {
        padding: 1rem;
      }
      
      .input-field {
        min-height: 50px;
        padding: 0.8rem 4rem 0.8rem 1rem;
      }
      
      .input-actions {
        right: 0.5rem;
        bottom: 0.5rem;
      }
      
      .edu-tools {
        bottom: 15px;
        right: 15px;
      }
      
      .tool-btn-main {
        width: 50px;
        height: 50px;
        font-size: 1.2rem;
      }
      
      .tool-panel {
        width: 280px;
        padding: 1rem;
      }
    }
    
    /* Scrollbar styles */
    ::-webkit-scrollbar {
      width: 8px;
    }
    
    ::-webkit-scrollbar-track {
      background: var(--secondary-bg);
    }
    
    ::-webkit-scrollbar-thumb {
      background: var(--tertiary-bg);
      border-radius: 4px;
    }
    
    ::-webkit-scrollbar-thumb:hover {
      background: #555;
    }
    
    /* Markdown-like styles for AI responses */
    .message-text strong {
      font-weight: 600;
    }
    
    .message-text em {
      font-style: italic;
    }
    
    .message-text code {
      font-family: monospace;
      background-color: rgba(0, 0, 0, 0.1);
      padding: 0.2rem 0.4rem;
      border-radius: 4px;
      font-size: 0.9em;
    }
    
    .message-text pre {
      background-color: var(--tertiary-bg);
      padding: 1rem;
      border-radius: var(--border-radius);
      overflow-x: auto;
      margin: 0.5rem 0;
    }
    
    .message-text ul, 
    .message-text ol {
      padding-left: 1.5rem;
      margin: 0.5rem 0;
    }
    
    .message-text li {
      margin-bottom: 0.3rem;
    }
    
    .message-text blockquote {
      border-left: 3px solid var(--accent-color);
      padding-left: 1rem;
      margin: 0.5rem 0;
      color: var(--secondary-text);
    }
    
    .message-text table {
      border-collapse: collapse;
      width: 100%;
      margin: 0.5rem 0;
    }
    
    .message-text th, 
    .message-text td {
      border: 1px solid var(--tertiary-bg);
      padding: 0.5rem;
      text-align: left;
    }
    
    .message-text th {
      background-color: var(--tertiary-bg);
    }