feat(frontend): Scholarchat-inspired UI refactor with top nav, sidebar, and message actions

- Add TopNav component with AI Chat, Study Guides, Progress tabs
- Refactor sidebar to include brand, new chat, subjects, chat history, settings
- Add message action buttons (Helpful, Note, Deeper) on assistant responses
- Enhance ChatInput with photo, mic attachment icons and AI disclaimer
- Improve welcome state with 2x2 suggested prompt grid
- Update global layout for proper sidebar offset (fix nav overlap)
- Remove obsolete Header component
- All styles: strict BEM naming, zero inline CSS, Paper Look theme

frontend/src/App.jsx

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+/* ========================================
+   App Component — padhLe
+   ======================================== */
+
+import { useState } from "react";
+import "./styles/App.css";
+import Sidebar from "./components/sidebar/Sidebar";
+import TopNav from "./components/top-nav/TopNav";
+import ChatHistory from "./components/chat-history/ChatHistory";
+import ChatInput from "./components/chat-input/ChatInput";
+
+function App() {
+  const [messages, setMessages] = useState([]);
+  const [activeSubject, setActiveSubject] = useState("science");
+  const [activeChat, setActiveChat] = useState(null);
+  const [activeTab, setActiveTab] = useState("chat");
+
+  const handleSend = (text) => {
+    if (!text.trim()) return;
+
+    // Add user message
+    setMessages((prev) => [...prev, { id: Date.now(), role: "user", text }]);
+
+    // TODO: Send to backend and get AI response
+    // Simulating AI response for now
+    setTimeout(() => {
+      setMessages((prev) => [
+        ...prev,
+        {
+          id: Date.now() + 1,
+          role: "assistant",
+          text: "This is a simulated response. Connect the backend to get real AI answers!",
+        },
+      ]);
+    }, 1000);
+  };
+
+  const handlePromptClick = (promptText) => {
+    handleSend(promptText);
+  };
+
+  return (
+    <div className="page">
+      {/* Left Sidebar — brand, subjects, chat history, settings */}
+      <Sidebar
+        activeSubject={activeSubject}
+        onSubjectChange={setActiveSubject}
+        activeChat={activeChat}
+        onChatSelect={setActiveChat}
+      />
+
+      <div className="page__main">
+        {/* Top Navigation — tabs + actions */}
+        <TopNav activeTab={activeTab} onTabChange={setActiveTab} />
+
+        {/* Chat Area */}
+        <div className="main-content">
+          <ChatHistory
+            messages={messages}
+            onPromptClick={handlePromptClick}
+          />
+        </div>
+
+        {/* Input Bar */}
+        <ChatInput onSend={handleSend} />
+      </div>
+    </div>
+  );
+}
+
+export default App;

frontend/src/components/chat-history/ChatHistory.css

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+/* ========================================
+   ChatHistory Component — padhLe
+   ======================================== */
+
+.chat-history {
+  flex: 1;
+  padding: var(--spacing-xl) 0;
+  overflow-y: auto;
+}
+
+.chat-history__list {
+  display: flex;
+  flex-direction: column;
+  gap: var(--spacing-xl);
+  padding-bottom: var(--spacing-xl);
+}
+
+/* Empty / Welcome State */
+.chat-history__empty {
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  min-height: 50vh;
+  text-align: center;
+  padding: var(--spacing-2xl);
+}
+
+.chat-history__empty-content {
+  max-width: 600px;
+}
+
+.chat-history__empty-title {
+  font-family: var(--font-heading);
+  font-size: 3rem;
+  font-weight: 700;
+  color: var(--color-text);
+  margin-bottom: var(--spacing-xs);
+}
+
+.chat-history__empty-tagline {
+  font-family: var(--font-body);
+  font-size: 1.05rem;
+  font-weight: 300;
+  color: var(--color-text-muted);
+  margin-bottom: var(--spacing-2xl);
+}
+
+/* Suggested Prompts */
+.chat-history__prompts {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: var(--spacing-sm);
+}
+
+.chat-history__prompt {
+  display: flex;
+  align-items: center;
+  gap: var(--spacing-sm);
+  padding: var(--spacing-md);
+  border: var(--border-thin);
+  border-radius: var(--border-radius);
+  background-color: var(--color-bg);
+  cursor: pointer;
+  text-align: left;
+  font-family: var(--font-body);
+  font-size: 0.9rem;
+  font-weight: 300;
+  color: var(--color-text);
+  line-height: 1.5;
+  transition: all var(--transition-fast);
+}
+
+.chat-history__prompt:hover {
+  background-color: var(--color-hover);
+  border-color: var(--color-text-muted);
+}
+
+.chat-history__prompt-icon {
+  font-size: 1.25rem;
+  flex-shrink: 0;
+}
+
+.chat-history__prompt-text {
+  color: var(--color-text);
+}

frontend/src/components/chat-history/ChatHistory.jsx

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+/* ========================================
+   ChatHistory Component — padhLe
+   ======================================== */
+
+import Message from "../message/Message";
+import "./ChatHistory.css";
+
+const ChatHistory = ({ messages, onPromptClick }) => {
+  const suggestedPrompts = [
+    { icon: "🧪", text: "Explain how photosynthesis works in simple terms" },
+    { icon: "📐", text: "Help me understand derivatives in calculus" },
+    { icon: "🏛️", text: "What caused the Industrial Revolution?" },
+    { icon: "📝", text: "Help me analyze themes in Romeo and Juliet" },
+  ];
+
+  const hasMessages = messages.length > 0;
+
+  return (
+    <div className="chat-history">
+      {hasMessages ? (
+        <div className="chat-history__list">
+          {messages.map((message) => (
+            <Message key={message.id} message={message} />
+          ))}
+        </div>
+      ) : (
+        <div className="chat-history__empty">
+          <div className="chat-history__empty-content">
+            <h2 className="chat-history__empty-title">
+              Welcome to padhLe
+            </h2>
+            <p className="chat-history__empty-tagline">
+              Your AI tutor for grades 6–12. Ask anything!
+            </p>
+
+            <div className="chat-history__prompts">
+              {suggestedPrompts.map((prompt, index) => (
+                <button
+                  key={index}
+                  className="chat-history__prompt"
+                  onClick={() => onPromptClick(prompt.text)}
+                >
+                  <span className="chat-history__prompt-icon">{prompt.icon}</span>
+                  <span className="chat-history__prompt-text">{prompt.text}</span>
+                </button>
+              ))}
+            </div>
+          </div>
+        </div>
+      )}
+    </div>
+  );
+};
+
+export default ChatHistory;

frontend/src/components/chat-input/ChatInput.css

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+/* ========================================
+   ChatInput Component — padhLe
+   ======================================== */
+
+.chat-input {
+  padding: var(--spacing-md) 0 var(--spacing-xl) 0;
+  border-top: var(--border-thin);
+  background-color: var(--color-bg);
+}
+
+.chat-input__wrapper {
+  max-width: 760px;
+  margin: 0 auto;
+}
+
+/* Form */
+.chat-input__form {
+  display: flex;
+  align-items: flex-end;
+  gap: var(--spacing-sm);
+  border: var(--border-thin);
+  border-radius: var(--border-radius);
+  padding: var(--spacing-sm) var(--spacing-md);
+  transition: border-color var(--transition-fast);
+}
+
+.chat-input__form:focus-within {
+  border-color: var(--color-accent);
+  box-shadow: 0 0 0 2px rgba(26, 26, 26, 0.08);
+}
+
+/* Attachments */
+.chat-input__attachments {
+  display: flex;
+  align-items: center;
+  gap: 2px;
+  padding-bottom: var(--spacing-xs);
+}
+
+.chat-input__attach-btn {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 32px;
+  height: 32px;
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  color: var(--color-text-muted);
+  opacity: 0.5;
+  transition: all var(--transition-fast);
+}
+
+.chat-input__attach-btn:hover {
+  background-color: var(--color-hover);
+  opacity: 1;
+}
+
+/* Textarea Field */
+.chat-input__field {
+  flex: 1;
+  font-family: var(--font-body);
+  font-size: 1rem;
+  font-weight: 300;
+  line-height: 1.6;
+  color: var(--color-text);
+  background-color: transparent;
+  border: none;
+  padding: var(--spacing-xs) 0;
+  resize: none;
+  outline: none;
+  min-height: 24px;
+  max-height: 200px;
+}
+
+.chat-input__field::placeholder {
+  color: var(--color-text-muted);
+  opacity: 0.5;
+}
+
+/* Submit Button */
+.chat-input__submit {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 36px;
+  height: 36px;
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: not-allowed;
+  opacity: 0.3;
+  transition: all var(--transition-fast);
+  flex-shrink: 0;
+}
+
+.chat-input__submit--active {
+  background-color: var(--color-accent);
+  color: var(--color-bg);
+  cursor: pointer;
+  opacity: 1;
+}
+
+.chat-input__submit--active:hover {
+  background-color: var(--color-text-muted);
+  transform: translateY(-1px);
+}
+
+/* Disclaimer */
+.chat-input__disclaimer {
+  font-size: 0.75rem;
+  color: var(--color-text-muted);
+  text-align: center;
+  margin-top: var(--spacing-sm);
+  opacity: 0.7;
+}

frontend/src/components/chat-input/ChatInput.jsx

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+/* ========================================
+   ChatInput Component — padhLe
+   ======================================== */
+
+import { useState, useRef, useEffect } from "react";
+import "./ChatInput.css";
+
+const ChatInput = ({ onSend }) => {
+  const [text, setText] = useState("");
+  const textareaRef = useRef(null);
+
+  // Auto-expand textarea as content grows
+  useEffect(() => {
+    if (textareaRef.current) {
+      textareaRef.current.style.height = "auto";
+      textareaRef.current.style.height = `${textareaRef.current.scrollHeight}px`;
+    }
+  }, [text]);
+
+  const handleSubmit = (e) => {
+    e.preventDefault();
+    if (text.trim()) {
+      onSend(text.trim());
+      setText("");
+      if (textareaRef.current) {
+        textareaRef.current.style.height = "auto";
+      }
+    }
+  };
+
+  const handleKeyDown = (e) => {
+    // Submit on Enter (not Shift+Enter)
+    if (e.key === "Enter" && !e.shiftKey) {
+      e.preventDefault();
+      handleSubmit(e);
+    }
+  };
+
+  return (
+    <div className="chat-input">
+      <div className="chat-input__wrapper">
+        <form className="chat-input__form" onSubmit={handleSubmit}>
+          {/* Attachment buttons */}
+          <div className="chat-input__attachments">
+            <button
+              type="button"
+              className="chat-input__attach-btn"
+              aria-label="Add photo"
+              title="Add photo"
+            >
+              <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+                <rect x="3" y="3" width="18" height="18" rx="2" ry="2" />
+                <circle cx="8.5" cy="8.5" r="1.5" />
+                <path d="M21 15l-5-5L5 21" />
+              </svg>
+            </button>
+            <button
+              type="button"
+              className="chat-input__attach-btn"
+              aria-label="Voice input"
+              title="Voice input"
+            >
+              <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+                <path d="M12 1a3 3 0 0 0-3 3v8a3 3 0 0 0 6 0V4a3 3 0 0 0-3-3z" />
+                <path d="M19 10v2a7 7 0 0 1-14 0v-2" />
+                <line x1="12" y1="19" x2="12" y2="23" />
+                <line x1="8" y1="23" x2="16" y2="23" />
+              </svg>
+            </button>
+          </div>
+
+          {/* Textarea */}
+          <textarea
+            ref={textareaRef}
+            className="chat-input__field"
+            placeholder="Ask anything about your subject..."
+            value={text}
+            onChange={(e) => setText(e.target.value)}
+            onKeyDown={handleKeyDown}
+            rows={1}
+          />
+
+          {/* Submit button */}
+          <button
+            className={`chat-input__submit ${
+              text.trim() ? "chat-input__submit--active" : ""
+            }`}
+            type="submit"
+            disabled={!text.trim()}
+            aria-label="Send message"
+          >
+            <svg
+              xmlns="http://www.w3.org/2000/svg"
+              viewBox="0 0 24 24"
+              fill="none"
+              stroke="currentColor"
+              strokeWidth="2"
+              strokeLinecap="round"
+              strokeLinejoin="round"
+              width="18"
+              height="18"
+            >
+              <path d="M22 2L15 22l-3-10-10 3z" />
+            </svg>
+          </button>
+        </form>
+
+        {/* AI Disclaimer */}
+        <p className="chat-input__disclaimer">
+          padhLe AI can make mistakes. Consider verifying important information.
+        </p>
+      </div>
+    </div>
+  );
+};
+
+export default ChatInput;

frontend/src/components/message/Message.css

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+/* ========================================
+   Message Component — padhLe
+   ======================================== */
+
+/* Base Message */
+.message {
+  display: flex;
+  flex-direction: column;
+  animation: messageFadeIn 0.3s ease;
+}
+
+@keyframes messageFadeIn {
+  from {
+    opacity: 0;
+    transform: translateY(10px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+/* Alignment */
+.message--user {
+  align-items: flex-end;
+}
+
+.message--assistant {
+  align-items: flex-start;
+}
+
+/* Bubble */
+.message__bubble {
+  max-width: 80%;
+  padding: var(--spacing-lg);
+  border-radius: var(--border-radius);
+  line-height: 1.6;
+}
+
+.message--assistant .message__bubble {
+  background-color: var(--color-bg);
+  border: var(--border-thin);
+}
+
+.message--user .message__bubble {
+  background-color: var(--color-accent);
+  color: var(--color-bg);
+  border: var(--border-thin);
+}
+
+/* Text */
+.message__text {
+  font-size: 1rem;
+  line-height: 1.6;
+  white-space: pre-wrap;
+}
+
+.message--assistant .message__text {
+  color: var(--color-text);
+}
+
+.message--user .message__text {
+  color: var(--color-bg);
+}
+
+/* Action Buttons */
+.message__actions {
+  display: flex;
+  align-items: center;
+  gap: var(--spacing-xs);
+  margin-top: var(--spacing-sm);
+  padding-left: var(--spacing-xs);
+}
+
+.message__action {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  padding: 4px var(--spacing-sm);
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  font-family: var(--font-body);
+  font-size: 0.75rem;
+  font-weight: 400;
+  color: var(--color-text-muted);
+  transition: all var(--transition-fast);
+}
+
+.message__action:hover {
+  background-color: var(--color-hover);
+  color: var(--color-text);
+}
+
+.message__action svg {
+  opacity: 0.6;
+}
+
+.message__action:hover svg {
+  opacity: 1;
+}

frontend/src/components/message/Message.jsx

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+/* ========================================
+   Message Component — padhLe
+   ======================================== */
+
+import "./Message.css";
+
+const Message = ({ message }) => {
+  const { role, text } = message;
+  const isUser = role === "user";
+
+  return (
+    <div className={`message ${isUser ? "message--user" : "message--assistant"}`}>
+      <div className="message__bubble">
+        <div className="message__text">{text}</div>
+      </div>
+
+      {/* Action buttons only for assistant messages */}
+      {!isUser && (
+        <div className="message__actions">
+          <button className="message__action" aria-label="Helpful" title="Helpful">
+            <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+              <path d="M7 22h4c1.1 0 2-.9 2-2v-4c0-.57-.24-1.09-.62-1.47L13 11.76c.38-.38.62-.9.62-1.47V7c0-1.1-.9-2-2-2H7c-1.1 0-2 .9-2 2v12c0 3.31 2.69 6 6 6h8v-2h-2.11c-.18-.5-.29-1.04-.29-1.6V22z" />
+            </svg>
+            <span>Helpful</span>
+          </button>
+          <button className="message__action" aria-label="Save note" title="Save Note">
+            <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+              <path d="M19 21l-7-5-7 5V5a2 2 0 0 1 2-2h10a2 2 0 0 1 2 2z" />
+            </svg>
+            <span>Note</span>
+          </button>
+          <button className="message__action" aria-label="Explain deeper" title="Explain Deeper">
+            <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+              <path d="M12 2a10 10 0 1 0 10 10H12V2z" />
+              <path d="M12 2a10 10 0 0 1 10 10" />
+            </svg>
+            <span>Deeper</span>
+          </button>
+        </div>
+      )}
+    </div>
+  );
+};
+
+export default Message;

frontend/src/components/sidebar/Sidebar.css

@@ -0,0 +1,220 @@
+/* ========================================
+   Sidebar Component — padhLe
+   ======================================== */
+
+/* Main Sidebar */
+.sidebar {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: var(--sidebar-width);
+  height: 100vh;
+  background-color: var(--color-bg);
+  border-right: var(--border-thin);
+  display: flex;
+  flex-direction: column;
+  padding: var(--spacing-lg);
+  overflow-y: auto;
+  z-index: 10;
+}
+
+/* Scrollbar styling */
+.sidebar::-webkit-scrollbar {
+  width: 4px;
+}
+
+.sidebar::-webkit-scrollbar-thumb {
+  background-color: var(--color-line);
+  border-radius: 2px;
+}
+
+/* Brand */
+.sidebar__brand {
+  padding-bottom: var(--spacing-md);
+  margin-bottom: var(--spacing-md);
+}
+
+.sidebar__title {
+  font-family: var(--font-heading);
+  font-size: 2.25rem;
+  font-weight: 700;
+  letter-spacing: 0.05em;
+  color: var(--color-text);
+}
+
+/* New Chat Button */
+.sidebar__new-chat {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: var(--spacing-xs);
+  width: 100%;
+  padding: var(--spacing-sm);
+  border: var(--border-thin);
+  border-radius: var(--border-radius);
+  background-color: var(--color-bg);
+  color: var(--color-text);
+  font-family: var(--font-body);
+  font-size: 0.9rem;
+  font-weight: 400;
+  cursor: pointer;
+  transition: all var(--transition-fast);
+  margin-bottom: var(--spacing-lg);
+}
+
+.sidebar__new-chat:hover {
+  background-color: var(--color-hover);
+  border-color: var(--color-text-muted);
+}
+
+/* Section */
+.sidebar__section {
+  margin-bottom: var(--spacing-md);
+}
+
+.sidebar__section--history {
+  flex: 1;
+  min-height: 0;
+  overflow-y: auto;
+}
+
+.sidebar__section-title {
+  font-size: 0.7rem;
+  font-weight: 500;
+  text-transform: uppercase;
+  letter-spacing: 0.1em;
+  color: var(--color-text-muted);
+  margin-bottom: var(--spacing-sm);
+  padding-left: var(--spacing-sm);
+}
+
+/* Subject List */
+.sidebar__list {
+  list-style: none;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+
+.sidebar__link {
+  display: flex;
+  align-items: center;
+  gap: var(--spacing-sm);
+  width: 100%;
+  padding: var(--spacing-sm);
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  font-family: var(--font-body);
+  font-size: 0.9rem;
+  font-weight: 300;
+  color: var(--color-text-muted);
+  text-align: left;
+  transition: all var(--transition-fast);
+}
+
+.sidebar__link:hover {
+  background-color: var(--color-hover);
+  color: var(--color-text);
+}
+
+.sidebar__link--active {
+  background-color: var(--color-accent);
+  color: var(--color-bg);
+}
+
+.sidebar__link--active:hover {
+  color: var(--color-bg);
+}
+
+.sidebar__icon {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 20px;
+  font-size: 0.95rem;
+}
+
+/* Chat List */
+.sidebar__chat-list {
+  list-style: none;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+
+.sidebar__chat-link {
+  display: flex;
+  flex-direction: column;
+  width: 100%;
+  padding: var(--spacing-sm);
+  padding-left: var(--spacing-sm);
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  font-family: var(--font-body);
+  text-align: left;
+  transition: all var(--transition-fast);
+}
+
+.sidebar__chat-link:hover {
+  background-color: var(--color-hover);
+}
+
+.sidebar__chat-link--active {
+  background-color: var(--color-hover);
+}
+
+.sidebar__chat-preview {
+  font-size: 0.85rem;
+  font-weight: 400;
+  color: var(--color-text);
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.sidebar__chat-time {
+  font-size: 0.7rem;
+  color: var(--color-text-muted);
+  margin-top: 2px;
+}
+
+/* Footer */
+.sidebar__footer {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  padding-top: var(--spacing-sm);
+  border-top: var(--border-thin);
+  margin-top: auto;
+}
+
+.sidebar__footer-btn {
+  display: flex;
+  align-items: center;
+  gap: var(--spacing-sm);
+  width: 100%;
+  padding: var(--spacing-sm);
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  font-family: var(--font-body);
+  font-size: 0.85rem;
+  font-weight: 300;
+  color: var(--color-text-muted);
+  text-align: left;
+  transition: all var(--transition-fast);
+}
+
+.sidebar__footer-btn:hover {
+  background-color: var(--color-hover);
+  color: var(--color-text);
+}
+
+.sidebar__footer-btn svg {
+  flex-shrink: 0;
+}

frontend/src/components/sidebar/Sidebar.jsx

@@ -0,0 +1,99 @@
+/* ========================================
+   Sidebar Component — padhLe
+   ======================================== */
+
+import "./Sidebar.css";
+
+const Sidebar = ({ activeSubject, onSubjectChange, activeChat, onChatSelect }) => {
+  const subjects = [
+    { id: "math", name: "Mathematics", icon: "∑" },
+    { id: "science", name: "Science", icon: "⚡" },
+    { id: "history", name: "History", icon: "📜" },
+    { id: "language", name: "Language Arts", icon: "✍" },
+    { id: "english", name: "English", icon: "📖" },
+    { id: "geography", name: "Geography", icon: "🌍" },
+  ];
+
+  const chats = [
+    { id: 1, preview: "Explain photosynthesis", time: "Today, 10:42 AM" },
+    { id: 2, preview: "Help with integrals", time: "Yesterday, 3:15 PM" },
+  ];
+
+  return (
+    <aside className="sidebar">
+      {/* Brand */}
+      <div className="sidebar__brand">
+        <h1 className="sidebar__title">padhLe</h1>
+      </div>
+
+      {/* New Chat Button */}
+      <button className="sidebar__new-chat">
+        <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+          <path d="M12 5v14M5 12h14" />
+        </svg>
+        <span>New Chat</span>
+      </button>
+
+      {/* Subjects */}
+      <div className="sidebar__section">
+        <h2 className="sidebar__section-title">Subjects</h2>
+        <ul className="sidebar__list">
+          {subjects.map((subject) => (
+            <li key={subject.id}>
+              <button
+                className={`sidebar__link ${
+                  activeSubject === subject.id ? "sidebar__link--active" : ""
+                }`}
+                onClick={() => onSubjectChange(subject.id)}
+              >
+                <span className="sidebar__icon">{subject.icon}</span>
+                <span className="sidebar__label">{subject.name}</span>
+              </button>
+            </li>
+          ))}
+        </ul>
+      </div>
+
+      {/* Chat History */}
+      <div className="sidebar__section sidebar__section--history">
+        <h2 className="sidebar__section-title">Chat History</h2>
+        <ul className="sidebar__chat-list">
+          {chats.map((chat) => (
+            <li key={chat.id}>
+              <button
+                className={`sidebar__chat-link ${
+                  activeChat === chat.id ? "sidebar__chat-link--active" : ""
+                }`}
+                onClick={() => onChatSelect(chat.id)}
+              >
+                <span className="sidebar__chat-preview">{chat.preview}</span>
+                <span className="sidebar__chat-time">{chat.time}</span>
+              </button>
+            </li>
+          ))}
+        </ul>
+      </div>
+
+      {/* Footer Actions */}
+      <div className="sidebar__footer">
+        <button className="sidebar__footer-btn" aria-label="Settings" title="Settings">
+          <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+            <circle cx="12" cy="12" r="3" />
+            <path d="M19.4 15a1.65 1.65 0 0 0 .33 1.82l.06.06a2 2 0 0 1 0 2.83 2 2 0 0 1-2.83 0l-.06-.06a1.65 1.65 0 0 0-1.82-.33 1.65 1.65 0 0 0-1 1.51V21a2 2 0 0 1-2 2 2 2 0 0 1-2-2v-.09A1.65 1.65 0 0 0 9 19.4a1.65 1.65 0 0 0-1.82.33l-.06.06a2 2 0 0 1-2.83 0 2 2 0 0 1 0-2.83l.06-.06A1.65 1.65 0 0 0 4.68 15a1.65 1.65 0 0 0-1.51-1H3a2 2 0 0 1-2-2 2 2 0 0 1 2-2h.09A1.65 1.65 0 0 0 4.6 9a1.65 1.65 0 0 0-.33-1.82l-.06-.06a2 2 0 0 1 0-2.83 2 2 0 0 1 2.83 0l.06.06A1.65 1.65 0 0 0 9 4.68a1.65 1.65 0 0 0 1-1.51V3a2 2 0 0 1 2-2 2 2 0 0 1 2 2v.09a1.65 1.65 0 0 0 1 1.51 1.65 1.65 0 0 0 1.82-.33l.06-.06a2 2 0 0 1 2.83 0 2 2 0 0 1 0 2.83l-.06.06a1.65 1.65 0 0 0-.33 1.82V9a1.65 1.65 0 0 0 1.51 1H21a2 2 0 0 1 2 2 2 2 0 0 1-2 2h-.09a1.65 1.65 0 0 0-1.51 1z" />
+          </svg>
+          <span>Settings</span>
+        </button>
+        <button className="sidebar__footer-btn" aria-label="Help" title="Help">
+          <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+            <circle cx="12" cy="12" r="10" />
+            <path d="M9.09 9a3 3 0 0 1 5.83 1c0 2-3 3-3 3" />
+            <path d="M12 17h.01" />
+          </svg>
+          <span>Help</span>
+        </button>
+      </div>
+    </aside>
+  );
+};
+
+export default Sidebar;

frontend/src/components/top-nav/TopNav.css

@@ -0,0 +1,86 @@
+/* ========================================
+   TopNav Component — padhLe
+   ======================================== */
+
+.topnav {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: var(--spacing-sm) var(--spacing-xl);
+  border-bottom: var(--border-thin);
+  background-color: var(--color-bg);
+  position: sticky;
+  top: 0;
+  z-index: 5;
+}
+
+/* Tab List */
+.topnav__tabs {
+  display: flex;
+  gap: var(--spacing-xs);
+}
+
+/* Individual Tab */
+.topnav__tab {
+  display: flex;
+  align-items: center;
+  gap: var(--spacing-xs);
+  padding: var(--spacing-sm) var(--spacing-md);
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  font-family: var(--font-body);
+  font-size: 0.9rem;
+  font-weight: 400;
+  color: var(--color-text-muted);
+  transition: all var(--transition-fast);
+}
+
+.topnav__tab:hover {
+  background-color: var(--color-hover);
+  color: var(--color-text);
+}
+
+.topnav__tab--active {
+  background-color: var(--color-accent);
+  color: var(--color-bg);
+}
+
+.topnav__tab--active:hover {
+  color: var(--color-bg);
+}
+
+.topnav__icon {
+  font-size: 1rem;
+}
+
+.topnav__label {
+  font-family: var(--font-body);
+}
+
+/* Action Buttons (Search, Notifications) */
+.topnav__actions {
+  display: flex;
+  align-items: center;
+  gap: var(--spacing-xs);
+}
+
+.topnav__action {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 36px;
+  height: 36px;
+  border: none;
+  background: transparent;
+  border-radius: var(--border-radius);
+  cursor: pointer;
+  color: var(--color-text-muted);
+  transition: all var(--transition-fast);
+}
+
+.topnav__action:hover {
+  background-color: var(--color-hover);
+  color: var(--color-text);
+}

frontend/src/components/top-nav/TopNav.jsx

@@ -0,0 +1,48 @@
+/* ========================================
+   TopNav Component — padhLe
+   ======================================== */
+
+import "./TopNav.css";
+
+const TopNav = ({ activeTab, onTabChange }) => {
+  const tabs = [
+    { id: "chat", label: "AI Chat", icon: "💬" },
+    { id: "study", label: "Study Guides", icon: "📖" },
+    { id: "progress", label: "Progress", icon: "📊" },
+  ];
+
+  return (
+    <nav className="topnav">
+      <div className="topnav__tabs">
+        {tabs.map((tab) => (
+          <button
+            key={tab.id}
+            className={`topnav__tab ${
+              activeTab === tab.id ? "topnav__tab--active" : ""
+            }`}
+            onClick={() => onTabChange(tab.id)}
+          >
+            <span className="topnav__icon">{tab.icon}</span>
+            <span className="topnav__label">{tab.label}</span>
+          </button>
+        ))}
+      </div>
+      <div className="topnav__actions">
+        <button className="topnav__action" aria-label="Search" title="Search">
+          <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+            <circle cx="11" cy="11" r="8" />
+            <path d="M21 21l-4.35-4.35" />
+          </svg>
+        </button>
+        <button className="topnav__action" aria-label="Notifications" title="Notifications">
+          <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+            <path d="M18 8A6 6 0 0 0 6 8c0 7-3 9-3 9h18s-3-2-3-9" />
+            <path d="M13.73 21a2 2 0 0 1-3.46 0" />
+          </svg>
+        </button>
+      </div>
+    </nav>
+  );
+};
+
+export default TopNav;

frontend/src/main.jsx

@@ -0,0 +1,14 @@
+/* ========================================
+   Main Entry Point — padhLe
+   ======================================== */
+
+import React from "react";
+import ReactDOM from "react-dom/client";
+import App from "./App.jsx";
+import "./styles/global.css";
+
+ReactDOM.createRoot(document.getElementById("root")).render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>
+);

frontend/src/styles/App.css

@@ -0,0 +1,6 @@
+/* ========================================
+   App Component — padhLe
+   ======================================== */
+
+/* All page styles are in global.css */
+/* This file is intentionally kept minimal */

frontend/src/styles/global.css

@@ -0,0 +1,86 @@
+/* ========================================
+   Global Styles — padhLe
+   ======================================== */
+
+/* Reset */
+*,
+*::before,
+*::after {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+/* Root Variables */
+:root {
+  --color-bg: #ffffff;
+  --color-border: #1a1a1a;
+  --color-text: #1a1a1a;
+  --color-text-muted: #555555;
+  --color-accent: #1a1a1a;
+  --color-line: #e8e8e8;
+  --color-hover: #f5f5f5;
+
+  --font-heading: "Caveat", cursive, sans-serif;
+  --font-body: "Inter", system-ui, sans-serif;
+
+  --border-thin: 1px solid var(--color-border);
+  --border-medium: 2px solid var(--color-border);
+  --border-radius: 4px;
+
+  --spacing-xs: 0.5rem;
+  --spacing-sm: 0.75rem;
+  --spacing-md: 1rem;
+  --spacing-lg: 1.5rem;
+  --spacing-xl: 2rem;
+  --spacing-2xl: 3rem;
+  --spacing-3xl: 4rem;
+  --spacing-4xl: 6rem;
+
+  --transition-fast: 150ms ease;
+  --transition-normal: 250ms ease;
+  --transition-slow: 350ms ease;
+
+  --sidebar-width: 240px;
+}
+
+/* Body */
+body {
+  font-family: var(--font-body);
+  font-weight: 300;
+  background-color: var(--color-bg);
+  color: var(--color-text);
+  line-height: 1.6;
+  min-height: 100vh;
+}
+
+/* Page Frame — sidebar + main layout */
+.page {
+  display: flex;
+  min-height: 100vh;
+  width: 100%;
+}
+
+/* Main Content Area — offset to right of fixed sidebar */
+.page__main {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  margin-left: var(--sidebar-width);
+  min-width: 0;
+}
+
+/* Main Content Wrapper (centered chat area) */
+.main-content {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  overflow-y: auto;
+}
+
+/* Container — centered content */
+.container {
+  max-width: 800px;
+  margin: 0 auto;
+  width: 100%;
+}