diff --git a/packages/app/src/App.vue b/packages/app/src/App.vue
index 5267439f..f266357c 100644
--- a/packages/app/src/App.vue
+++ b/packages/app/src/App.vue
@@ -1,5 +1,5 @@
 <template>
-  <div class="h-dvh flex flex-col bg-gray-50 text-gray-900 dark:bg-gray-950 dark:text-gray-100">
+  <div class="h-dvh flex flex-col">
     <RouterView />
   </div>
 </template>
diff --git a/packages/app/src/components/chat/ChatHeader.vue b/packages/app/src/components/chat/ChatHeader.vue
new file mode 100644
index 00000000..2daefa2d
--- /dev/null
+++ b/packages/app/src/components/chat/ChatHeader.vue
@@ -0,0 +1,63 @@
+<template>
+  <div class="glass-subtle rounded-t-2xl flex items-center justify-between px-4 py-3">
+    <div class="flex items-center gap-3 min-w-0">
+      <div class="w-8 h-8 rounded-full bg-accent/20 flex items-center justify-center shrink-0">
+        <span class="text-accent text-sm font-bold">AI</span>
+      </div>
+      <div class="min-w-0">
+        <h2 class="text-sm font-semibold text-white truncate">{{ title }}</h2>
+        <p class="text-[10px] text-white/40 truncate">{{ conversationId }}</p>
+      </div>
+    </div>
+
+    <div class="flex items-center gap-1">
+      <button
+        class="p-2 rounded-lg text-white/40 hover:text-white/80 hover:bg-white/5 transition-all duration-200"
+        :title="side === 'right' ? 'Move panel to left' : 'Move panel to right'"
+        aria-label="Switch panel side"
+        @click="$emit('switchSide')"
+      >
+        <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path v-if="side === 'right'" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M11 19l-7-7 7-7m8 14l-7-7 7-7" />
+          <path v-else stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M13 5l7 7-7 7M5 5l7 7-7 7" />
+        </svg>
+      </button>
+
+      <button
+        class="p-2 rounded-lg text-white/40 hover:text-white/80 hover:bg-white/5 transition-all duration-200"
+        aria-label="New conversation"
+        @click="$emit('newChat')"
+      >
+        <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 4v16m8-8H4" />
+        </svg>
+      </button>
+
+      <button
+        v-if="showClose"
+        class="p-2 rounded-lg text-white/40 hover:text-white/80 hover:bg-white/5 transition-all duration-200"
+        aria-label="Close"
+        @click="$emit('close')"
+      >
+        <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12" />
+        </svg>
+      </button>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+defineProps<{
+  title: string
+  conversationId: string
+  side: 'left' | 'right'
+  showClose?: boolean
+}>()
+
+defineEmits<{
+  switchSide: []
+  newChat: []
+  close: []
+}>()
+</script>
diff --git a/packages/app/src/components/chat/ChatInput.vue b/packages/app/src/components/chat/ChatInput.vue
new file mode 100644
index 00000000..5d04b132
--- /dev/null
+++ b/packages/app/src/components/chat/ChatInput.vue
@@ -0,0 +1,72 @@
+<template>
+  <div class="p-3 md:p-4">
+    <div
+      class="glass rounded-2xl px-4 py-3 flex items-end gap-3 transition-all duration-300 inner-glow"
+      :class="isFocused ? 'border-white/20 glow-soft' : ''"
+    >
+      <textarea
+        ref="textareaRef"
+        v-model="text"
+        rows="1"
+        :placeholder="placeholder"
+        class="flex-1 resize-none bg-transparent text-sm text-white outline-none placeholder:text-white/30 min-h-[24px] max-h-[120px]"
+        @focus="isFocused = true"
+        @blur="isFocused = false"
+        @keydown.enter.exact.prevent="send"
+        @input="autoResize"
+      />
+      <button
+        :disabled="!canSend"
+        class="shrink-0 w-9 h-9 flex items-center justify-center rounded-xl transition-all duration-200"
+        :class="canSend
+          ? 'bg-accent text-white hover:bg-accent-hover active:scale-90'
+          : 'bg-white/5 text-white/20 cursor-not-allowed'"
+        aria-label="Send message"
+        @click="send"
+      >
+        <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 12L3.269 3.126A59.768 59.768 0 0121.485 12 59.77 59.77 0 013.27 20.876L5.999 12zm0 0h7.5" />
+        </svg>
+      </button>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, computed, nextTick } from 'vue'
+
+const props = withDefaults(
+  defineProps<{
+    disabled?: boolean
+    placeholder?: string
+  }>(),
+  {
+    disabled: false,
+    placeholder: 'Message AIUI...',
+  }
+)
+
+const emit = defineEmits<{
+  send: [text: string]
+}>()
+
+const text = ref('')
+const isFocused = ref(false)
+const textareaRef = ref<HTMLTextAreaElement | null>(null)
+
+const canSend = computed(() => text.value.trim().length > 0 && !props.disabled)
+
+function send() {
+  if (!canSend.value) return
+  emit('send', text.value.trim())
+  text.value = ''
+  nextTick(autoResize)
+}
+
+function autoResize() {
+  const el = textareaRef.value
+  if (!el) return
+  el.style.height = 'auto'
+  el.style.height = Math.min(el.scrollHeight, 120) + 'px'
+}
+</script>
diff --git a/packages/app/src/components/chat/ChatMessage.vue b/packages/app/src/components/chat/ChatMessage.vue
new file mode 100644
index 00000000..277edaaf
--- /dev/null
+++ b/packages/app/src/components/chat/ChatMessage.vue
@@ -0,0 +1,43 @@
+<template>
+  <div
+    class="flex animate-fade-up"
+    :class="isUser ? 'justify-end' : 'justify-start'"
+    :style="{ animationDelay: `${index * 30}ms` }"
+  >
+    <div
+      class="max-w-[85%] md:max-w-[70%] rounded-2xl px-4 py-3 transition-all duration-200"
+      :class="bubbleClasses"
+    >
+      <p class="text-sm leading-relaxed whitespace-pre-wrap break-words">{{ message.content }}</p>
+      <div class="flex items-center gap-2 mt-1.5">
+        <span class="text-[10px] opacity-40 select-none">{{ formattedTime }}</span>
+        <span v-if="isUser && message.status" class="text-[10px] opacity-30">
+          {{ message.status === 'sent' ? '✓' : message.status === 'delivered' ? '✓✓' : '' }}
+        </span>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { computed } from 'vue'
+import type { Message } from '@aiui/core/types/message'
+
+const props = defineProps<{
+  message: Message
+  index: number
+}>()
+
+const isUser = computed(() => props.message.role === 'user')
+
+const bubbleClasses = computed(() =>
+  isUser.value
+    ? 'glass-strong text-white rounded-br-md'
+    : 'glass-dark text-gray-100 rounded-bl-md'
+)
+
+const formattedTime = computed(() => {
+  const d = new Date(props.message.timestamp)
+  return d.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' })
+})
+</script>
diff --git a/packages/app/src/components/chat/ChatWindow.vue b/packages/app/src/components/chat/ChatWindow.vue
new file mode 100644
index 00000000..e4808600
--- /dev/null
+++ b/packages/app/src/components/chat/ChatWindow.vue
@@ -0,0 +1,122 @@
+<template>
+  <div
+    class="flex flex-col h-full rounded-2xl overflow-hidden transition-all duration-300"
+    :class="variant === 'modal' ? 'glass-dark' : ''"
+  >
+    <ChatHeader
+      :title="title"
+      :conversation-id="displayId"
+      :side="side"
+      :show-close="showClose"
+      @switch-side="$emit('switchSide')"
+      @new-chat="handleNewChat"
+      @close="$emit('close')"
+    />
+
+    <div
+      ref="messageListRef"
+      class="flex-1 overflow-y-auto scrollbar-thin p-4 space-y-3"
+    >
+      <div v-if="messages.length === 0" class="flex items-center justify-center h-full">
+        <div class="text-center space-y-3 animate-fade-up">
+          <div class="w-16 h-16 rounded-2xl glass flex items-center justify-center mx-auto">
+            <span class="text-2xl">✦</span>
+          </div>
+          <p class="text-sm text-white/30">Start a conversation</p>
+        </div>
+      </div>
+
+      <ChatMessage
+        v-for="(msg, i) in messages"
+        :key="msg.id"
+        :message="msg"
+        :index="i"
+      />
+
+      <StreamingDots v-if="isStreaming && lastMessageEmpty" />
+    </div>
+
+    <ChatInput
+      :disabled="isStreaming"
+      :placeholder="isStreaming ? 'Waiting for response...' : 'Message AIUI...'"
+      @send="handleSend"
+    />
+  </div>
+</template>
+
+<script setup lang="ts">
+import { computed, ref, watch, nextTick } from 'vue'
+import { useChatStore } from '@/stores/chat'
+import { useAI } from '@/composables/useAI'
+import ChatHeader from './ChatHeader.vue'
+import ChatMessage from './ChatMessage.vue'
+import ChatInput from './ChatInput.vue'
+import StreamingDots from './StreamingDots.vue'
+
+withDefaults(
+  defineProps<{
+    variant?: 'standalone' | 'modal'
+    side?: 'left' | 'right'
+    showClose?: boolean
+  }>(),
+  {
+    variant: 'standalone',
+    side: 'right',
+    showClose: false,
+  }
+)
+
+defineEmits<{
+  switchSide: []
+  close: []
+}>()
+
+const chatStore = useChatStore()
+const { sendMessage } = useAI()
+const messageListRef = ref<HTMLElement | null>(null)
+
+const messages = computed(() => chatStore.messages)
+const isStreaming = computed(() => chatStore.isStreaming)
+
+const title = computed(
+  () => chatStore.activeConversation?.title ?? 'New Chat'
+)
+
+const displayId = computed(
+  () => chatStore.activeConversationId?.slice(0, 8) ?? '—'
+)
+
+const lastMessageEmpty = computed(() => {
+  const msgs = messages.value
+  if (msgs.length === 0) return true
+  return msgs[msgs.length - 1].content === ''
+})
+
+function handleNewChat() {
+  chatStore.createConversation()
+}
+
+async function handleSend(text: string) {
+  await sendMessage(text)
+}
+
+watch(
+  () => messages.value.length,
+  () => {
+    nextTick(() => {
+      const el = messageListRef.value
+      if (el) el.scrollTop = el.scrollHeight
+    })
+  }
+)
+
+watch(
+  () => messages.value[messages.value.length - 1]?.content,
+  () => {
+    nextTick(() => {
+      const el = messageListRef.value
+      if (el) el.scrollTop = el.scrollHeight
+    })
+  }
+)
+</script>
diff --git a/packages/app/src/components/chat/StreamingDots.vue b/packages/app/src/components/chat/StreamingDots.vue
new file mode 100644
index 00000000..4eadf523
--- /dev/null
+++ b/packages/app/src/components/chat/StreamingDots.vue
@@ -0,0 +1,14 @@
+<template>
+  <div class="flex justify-start animate-fade-up">
+    <div class="glass-dark rounded-2xl rounded-bl-md px-4 py-3">
+      <div class="flex items-center gap-1.5">
+        <span
+          v-for="i in 3"
+          :key="i"
+          class="w-1.5 h-1.5 rounded-full bg-white/40 animate-pulse-glow"
+          :style="{ animationDelay: `${i * 200}ms` }"
+        />
+      </div>
+    </div>
+  </div>
+</template>
diff --git a/packages/app/src/components/widget/AIUIWidget.vue b/packages/app/src/components/widget/AIUIWidget.vue
new file mode 100644
index 00000000..ca5486d0
--- /dev/null
+++ b/packages/app/src/components/widget/AIUIWidget.vue
@@ -0,0 +1,32 @@
+<template>
+  <div>
+    <WidgetFab
+      :is-open="isOpen"
+      :position="fabPosition"
+      @toggle="isOpen = !isOpen"
+    />
+    <WidgetModal
+      :is-open="isOpen"
+      :side="side"
+      @close="isOpen = false"
+      @switch-side="toggleSide"
+    />
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ref, computed } from 'vue'
+import WidgetFab from './WidgetFab.vue'
+import WidgetModal from './WidgetModal.vue'
+
+const isOpen = ref(false)
+const side = ref<'left' | 'right'>('right')
+
+const fabPosition = computed(() =>
+  side.value === 'left' ? 'bottom-left' : 'bottom-right'
+)
+
+function toggleSide() {
+  side.value = side.value === 'right' ? 'left' : 'right'
+}
+</script>
diff --git a/packages/app/src/components/widget/WidgetFab.vue b/packages/app/src/components/widget/WidgetFab.vue
new file mode 100644
index 00000000..ce6d5655
--- /dev/null
+++ b/packages/app/src/components/widget/WidgetFab.vue
@@ -0,0 +1,53 @@
+<template>
+  <button
+    class="fixed z-50 w-14 h-14 rounded-full glass-strong flex items-center justify-center
+           shadow-lg hover:shadow-xl transition-all duration-300
+           hover:scale-105 active:scale-95 glow-accent"
+    :class="positionClasses"
+    :aria-label="isOpen ? 'Close AIUI' : 'Open AIUI'"
+    @click="$emit('toggle')"
+  >
+    <svg
+      class="w-6 h-6 text-accent transition-transform duration-300"
+      :class="isOpen ? 'rotate-45' : ''"
+      fill="none"
+      stroke="currentColor"
+      viewBox="0 0 24 24"
+    >
+      <path
+        v-if="!isOpen"
+        stroke-linecap="round"
+        stroke-linejoin="round"
+        stroke-width="2"
+        d="M8 12h.01M12 12h.01M16 12h.01M21 12c0 4.418-4.03 8-9 8a9.863 9.863 0 01-4.255-.949L3 20l1.395-3.72C3.512 15.042 3 13.574 3 12c0-4.418 4.03-8 9-8s9 3.582 9 8z"
+      />
+      <path
+        v-else
+        stroke-linecap="round"
+        stroke-linejoin="round"
+        stroke-width="2"
+        d="M12 4v16m8-8H4"
+      />
+    </svg>
+  </button>
+</template>
+
+<script setup lang="ts">
+import { computed } from 'vue'
+
+const props = withDefaults(
+  defineProps<{
+    isOpen: boolean
+    position?: 'bottom-right' | 'bottom-left'
+  }>(),
+  { position: 'bottom-right' }
+)
+
+defineEmits<{ toggle: [] }>()
+
+const positionClasses = computed(() =>
+  props.position === 'bottom-left'
+    ? 'bottom-6 left-6'
+    : 'bottom-6 right-6'
+)
+</script>
diff --git a/packages/app/src/components/widget/WidgetModal.vue b/packages/app/src/components/widget/WidgetModal.vue
new file mode 100644
index 00000000..02144a37
--- /dev/null
+++ b/packages/app/src/components/widget/WidgetModal.vue
@@ -0,0 +1,65 @@
+<template>
+  <Teleport to="body">
+    <Transition name="widget">
+      <div
+        v-if="isOpen"
+        class="fixed z-40 animate-scale-in"
+        :class="positionClasses"
+      >
+        <div
+          class="w-[380px] h-[600px] md:w-[420px] md:h-[640px] rounded-2xl overflow-hidden shadow-2xl"
+          :style="{ boxShadow: '0 20px 60px rgba(0, 0, 0, 0.5), 0 0 40px rgba(247, 147, 26, 0.08)' }"
+        >
+          <ChatWindow
+            variant="modal"
+            :side="side"
+            show-close
+            @switch-side="$emit('switchSide')"
+            @close="$emit('close')"
+          />
+        </div>
+      </div>
+    </Transition>
+  </Teleport>
+</template>
+
+<script setup lang="ts">
+import { computed } from 'vue'
+import ChatWindow from '@/components/chat/ChatWindow.vue'
+
+const props = withDefaults(
+  defineProps<{
+    isOpen: boolean
+    side?: 'left' | 'right'
+  }>(),
+  { side: 'right' }
+)
+
+defineEmits<{
+  close: []
+  switchSide: []
+}>()
+
+const positionClasses = computed(() =>
+  props.side === 'left'
+    ? 'bottom-24 left-6'
+    : 'bottom-24 right-6'
+)
+</script>
+
+<style scoped>
+.widget-enter-active {
+  transition: all 0.25s cubic-bezier(0.16, 1, 0.3, 1);
+}
+.widget-leave-active {
+  transition: all 0.2s ease-in;
+}
+.widget-enter-from {
+  opacity: 0;
+  transform: scale(0.9) translateY(20px);
+}
+.widget-leave-to {
+  opacity: 0;
+  transform: scale(0.9) translateY(20px);
+}
+</style>
diff --git a/packages/app/src/composables/useAI.ts b/packages/app/src/composables/useAI.ts
new file mode 100644
index 00000000..13028651
--- /dev/null
+++ b/packages/app/src/composables/useAI.ts
@@ -0,0 +1,108 @@
+import { useChatStore } from '@/stores/chat'
+
+const OPENROUTER_URL = 'https://openrouter.ai/api/v1/chat/completions'
+
+interface OpenRouterMessage {
+  role: 'system' | 'user' | 'assistant'
+  content: string
+}
+
+export function useAI() {
+  const chatStore = useChatStore()
+
+  async function sendMessage(userText: string) {
+    const apiKey = import.meta.env.VITE_OPENROUTER_API_KEY
+    if (!apiKey) {
+      console.error('VITE_OPENROUTER_API_KEY not set in .env.local')
+      return
+    }
+
+    let convId = chatStore.activeConversationId
+    if (!convId) {
+      convId = chatStore.createConversation()
+    }
+
+    chatStore.addMessage(convId, { role: 'user', content: userText })
+
+    const assistantMsg = chatStore.addMessage(convId, { role: 'assistant', content: '' })
+    if (!assistantMsg) return
+
+    chatStore.isStreaming = true
+
+    const history: OpenRouterMessage[] = chatStore.messages
+      .filter((m) => m.id !== assistantMsg.id)
+      .map((m) => ({ role: m.role as 'user' | 'assistant', content: m.content }))
+
+    try {
+      const res = await fetch(OPENROUTER_URL, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          'Authorization': `Bearer ${apiKey}`,
+          'HTTP-Referer': window.location.origin,
+          'X-Title': 'AIUI',
+        },
+        body: JSON.stringify({
+          model: 'meta-llama/llama-4-maverick:free',
+          messages: [
+            {
+              role: 'system',
+              content: 'You are AIUI, a helpful AI assistant. Be concise and helpful. When discussing films, provide rich details including genre, year, director, and rating.',
+            },
+            ...history,
+          ],
+          stream: true,
+        }),
+      })
+
+      if (!res.ok) {
+        const err = await res.text()
+        chatStore.appendToLastMessage(convId, `Error: ${res.status} — ${err}`)
+        chatStore.isStreaming = false
+        return
+      }
+
+      const reader = res.body?.getReader()
+      const decoder = new TextDecoder()
+
+      if (!reader) {
+        chatStore.appendToLastMessage(convId, 'Error: No response body')
+        chatStore.isStreaming = false
+        return
+      }
+
+      let buffer = ''
+      while (true) {
+        const { done, value } = await reader.read()
+        if (done) break
+
+        buffer += decoder.decode(value, { stream: true })
+        const lines = buffer.split('\n')
+        buffer = lines.pop() ?? ''
+
+        for (const line of lines) {
+          const trimmed = line.trim()
+          if (!trimmed || !trimmed.startsWith('data: ')) continue
+          const data = trimmed.slice(6)
+          if (data === '[DONE]') break
+
+          try {
+            const parsed = JSON.parse(data)
+            const delta = parsed.choices?.[0]?.delta?.content
+            if (delta) {
+              chatStore.appendToLastMessage(convId, delta)
+            }
+          } catch {
+            // skip malformed chunks
+          }
+        }
+      }
+    } catch (err) {
+      chatStore.appendToLastMessage(convId, `\n\nConnection error: ${err instanceof Error ? err.message : 'Unknown error'}`)
+    } finally {
+      chatStore.isStreaming = false
+    }
+  }
+
+  return { sendMessage }
+}
diff --git a/packages/app/src/composables/useTheme.ts b/packages/app/src/composables/useTheme.ts
new file mode 100644
index 00000000..7f519ba6
--- /dev/null
+++ b/packages/app/src/composables/useTheme.ts
@@ -0,0 +1,30 @@
+import { ref, computed } from 'vue'
+
+type ThemeName = 'dark' | 'light'
+
+const currentTheme = ref<ThemeName>('dark')
+
+export function useTheme() {
+  const isDark = computed(() => currentTheme.value === 'dark')
+
+  const setTheme = (theme: ThemeName) => {
+    currentTheme.value = theme
+    localStorage.setItem('aiui-theme', theme)
+    document.documentElement.classList.toggle('dark', theme === 'dark')
+  }
+
+  const toggleTheme = () => {
+    setTheme(isDark.value ? 'light' : 'dark')
+  }
+
+  const initTheme = () => {
+    const saved = localStorage.getItem('aiui-theme') as ThemeName | null
+    if (saved) {
+      setTheme(saved)
+    } else if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
+      setTheme('dark')
+    }
+  }
+
+  return { currentTheme, isDark, setTheme, toggleTheme, initTheme }
+}
diff --git a/packages/app/src/main.ts b/packages/app/src/main.ts
index 009879e4..469165ee 100644
--- a/packages/app/src/main.ts
+++ b/packages/app/src/main.ts
@@ -12,6 +12,11 @@ const router = createRouter({
       name: 'chat',
       component: () => import('./pages/ChatPage.vue'),
     },
+    {
+      path: '/widget-demo',
+      name: 'widget-demo',
+      component: () => import('./pages/WidgetDemoPage.vue'),
+    },
   ],
 })
 
diff --git a/packages/app/src/pages/ChatPage.vue b/packages/app/src/pages/ChatPage.vue
index 35de3ae3..a723fe2c 100644
--- a/packages/app/src/pages/ChatPage.vue
+++ b/packages/app/src/pages/ChatPage.vue
@@ -1,43 +1,94 @@
 <template>
-  <div class="flex h-full">
-    <main class="flex-1 flex flex-col min-w-0">
-      <header class="flex items-center justify-between px-4 py-3 border-b border-gray-200 dark:border-gray-800">
-        <h1 class="text-lg font-semibold">AIUI</h1>
-        <span class="text-xs text-gray-400">Phase 0 — Foundation</span>
-      </header>
+  <div class="h-full flex flex-col bg-gradient-to-br from-gray-950 via-gray-900 to-gray-950 relative overflow-hidden">
+    <div class="absolute inset-0 pointer-events-none">
+      <div class="absolute top-[-20%] left-[-10%] w-[500px] h-[500px] rounded-full bg-accent/5 blur-[120px]" />
+      <div class="absolute bottom-[-20%] right-[-10%] w-[600px] h-[600px] rounded-full bg-info/5 blur-[120px]" />
+    </div>
 
-      <div class="flex-1 overflow-y-auto p-4">
-        <div class="max-w-3xl mx-auto space-y-4">
-          <p class="text-sm text-gray-500 text-center py-12">
-            Start a conversation. Ask about films, code, or anything else.
+    <div class="relative z-10 flex-1 flex h-full p-3 md:p-4 gap-3 md:gap-4" :class="layoutClasses">
+      <aside
+        v-if="showSidebar"
+        class="hidden lg:flex w-64 xl:w-72 shrink-0 flex-col glass rounded-2xl overflow-hidden"
+      >
+        <div class="p-4 flex items-center justify-between">
+          <h1 class="text-lg font-bold gradient-text">AIUI</h1>
+          <button
+            class="p-2 rounded-lg text-white/40 hover:text-white hover:bg-white/5 transition-all"
+            aria-label="New chat"
+            @click="chatStore.createConversation()"
+          >
+            <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 4v16m8-8H4" />
+            </svg>
+          </button>
+        </div>
+
+        <div class="flex-1 overflow-y-auto scrollbar-thin px-2 pb-2 space-y-1">
+          <button
+            v-for="conv in conversations"
+            :key="conv.id"
+            class="w-full text-left px-3 py-2.5 rounded-xl text-sm transition-all duration-200 truncate"
+            :class="conv.id === chatStore.activeConversationId
+              ? 'glass-strong text-white'
+              : 'text-white/50 hover:text-white/80 hover:bg-white/5'"
+            @click="chatStore.setActiveConversation(conv.id)"
+          >
+            {{ conv.title }}
+          </button>
+
+          <p
+            v-if="conversations.length === 0"
+            class="text-xs text-white/20 text-center py-8"
+          >
+            No conversations yet
           </p>
         </div>
-      </div>
 
-      <div class="border-t border-gray-200 dark:border-gray-800 p-4">
-        <div class="max-w-3xl mx-auto">
-          <div
-            class="flex items-end gap-2 rounded-2xl border border-gray-300 dark:border-gray-700 bg-white dark:bg-gray-900 px-4 py-3 focus-within:border-primary focus-within:ring-2 focus-within:ring-primary/20 transition-colors"
-          >
-            <textarea
-              rows="1"
-              placeholder="Message AIUI..."
-              class="flex-1 resize-none bg-transparent text-base outline-none placeholder:text-gray-400 min-h-[24px] max-h-[200px]"
-            />
-            <button
-              class="shrink-0 w-8 h-8 flex items-center justify-center rounded-lg bg-primary text-white hover:bg-primary-dark transition-colors"
-              aria-label="Send message"
-            >
-              <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M5 12h14m-7-7l7 7-7 7" />
-              </svg>
-            </button>
+        <div class="p-3 border-t border-white/5">
+          <div class="flex items-center gap-2 px-2 py-1.5 rounded-lg text-[11px] text-white/25">
+            <span class="w-1.5 h-1.5 rounded-full bg-success animate-pulse" />
+            <span>OpenRouter connected</span>
           </div>
         </div>
-      </div>
-    </main>
+      </aside>
+
+      <main class="flex-1 min-w-0 flex flex-col glass rounded-2xl overflow-hidden">
+        <ChatWindow
+          :side="panelSide"
+          @switch-side="chatStore.switchSide()"
+        />
+      </main>
+
+      <aside
+        v-if="false"
+        class="hidden xl:flex w-80 shrink-0 flex-col glass rounded-2xl overflow-hidden"
+      >
+        <div class="p-4 text-center text-white/20 text-sm">
+          Content panel (coming soon)
+        </div>
+      </aside>
+    </div>
   </div>
 </template>
 
 <script setup lang="ts">
+import { computed, onMounted } from 'vue'
+import { useChatStore } from '@/stores/chat'
+import { useTheme } from '@/composables/useTheme'
+import ChatWindow from '@/components/chat/ChatWindow.vue'
+
+const chatStore = useChatStore()
+const { initTheme } = useTheme()
+
+const panelSide = computed(() => chatStore.panelSide)
+const conversations = computed(() => chatStore.conversationList)
+const showSidebar = true
+
+const layoutClasses = computed(() =>
+  panelSide.value === 'left' ? 'flex-row-reverse' : 'flex-row'
+)
+
+onMounted(() => {
+  initTheme()
+})
 </script>
diff --git a/packages/app/src/pages/WidgetDemoPage.vue b/packages/app/src/pages/WidgetDemoPage.vue
new file mode 100644
index 00000000..7beda2d4
--- /dev/null
+++ b/packages/app/src/pages/WidgetDemoPage.vue
@@ -0,0 +1,159 @@
+<template>
+  <div class="min-h-full bg-white text-gray-900 font-sans">
+    <nav class="border-b border-gray-200 bg-white sticky top-0 z-30">
+      <div class="max-w-6xl mx-auto px-6 py-4 flex items-center justify-between">
+        <div class="flex items-center gap-3">
+          <div class="w-8 h-8 rounded-lg bg-blue-600 flex items-center justify-center">
+            <span class="text-white text-sm font-bold">A</span>
+          </div>
+          <span class="text-lg font-semibold">Acme App</span>
+        </div>
+        <div class="flex items-center gap-6 text-sm text-gray-600">
+          <a href="#" class="hover:text-gray-900">Dashboard</a>
+          <a href="#" class="hover:text-gray-900">Projects</a>
+          <a href="#" class="hover:text-gray-900">Settings</a>
+          <RouterLink to="/" class="text-accent font-medium hover:underline">
+            ← Back to AIUI
+          </RouterLink>
+        </div>
+      </div>
+    </nav>
+
+    <div class="max-w-6xl mx-auto px-6 py-12">
+      <div class="mb-12">
+        <h1 class="text-3xl font-bold mb-2">Widget Integration Demo</h1>
+        <p class="text-gray-500 max-w-2xl">
+          This page simulates a third-party web application with the AIUI chat widget embedded.
+          Click the floating button in the bottom corner to open the AI assistant.
+          You can also switch which side it appears on.
+        </p>
+      </div>
+
+      <div class="grid md:grid-cols-2 lg:grid-cols-3 gap-6 mb-16">
+        <div v-for="n in 6" :key="n" class="bg-gray-50 rounded-2xl p-6 border border-gray-100">
+          <div class="w-10 h-10 rounded-xl bg-blue-100 text-blue-600 flex items-center justify-center mb-4">
+            <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 12h6m-6 4h6m2 5H7a2 2 0 01-2-2V5a2 2 0 012-2h5.586a1 1 0 01.707.293l5.414 5.414a1 1 0 01.293.707V19a2 2 0 01-2 2z" />
+            </svg>
+          </div>
+          <h3 class="font-semibold mb-1">Project {{ n }}</h3>
+          <p class="text-sm text-gray-500 mb-3">
+            Sample content card demonstrating how the widget overlays existing UI without disruption.
+          </p>
+          <div class="flex items-center gap-2">
+            <span class="px-2.5 py-0.5 text-xs font-medium rounded-full bg-green-100 text-green-700">Active</span>
+            <span class="text-xs text-gray-400">Updated 2h ago</span>
+          </div>
+        </div>
+      </div>
+
+      <div class="bg-gray-50 rounded-2xl border border-gray-200 p-8 mb-16">
+        <h2 class="text-xl font-bold mb-4">How to embed AIUI in your app</h2>
+        <div class="space-y-6 text-sm text-gray-700">
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">Option 1: Script Tag (simplest)</h3>
+            <pre class="bg-gray-900 text-gray-100 rounded-lg p-4 overflow-x-auto text-xs"><code>&lt;script src="https://cdn.example.com/aiui-widget.js"&gt;&lt;/script&gt;
+&lt;script&gt;
+  AIUI.init({
+    apiKey: 'your-openrouter-key',
+    position: 'bottom-right',  // or 'bottom-left'
+    theme: 'dark',
+  })
+&lt;/script&gt;</code></pre>
+          </div>
+
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">Option 2: Web Component</h3>
+            <pre class="bg-gray-900 text-gray-100 rounded-lg p-4 overflow-x-auto text-xs"><code>&lt;!-- Load the custom element --&gt;
+&lt;script type="module" src="https://cdn.example.com/aiui-element.js"&gt;&lt;/script&gt;
+
+&lt;!-- Use anywhere in your HTML --&gt;
+&lt;aiui-chat
+  api-key="your-key"
+  position="bottom-right"
+  theme="dark"
+&gt;&lt;/aiui-chat&gt;</code></pre>
+          </div>
+
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">Option 3: npm package (Vue/React/Svelte)</h3>
+            <pre class="bg-gray-900 text-gray-100 rounded-lg p-4 overflow-x-auto text-xs"><code>npm install @aiui/widget
+
+// Vue 3
+import { AIUIWidget } from '@aiui/widget'
+app.use(AIUIWidget, {
+  apiKey: 'your-key',
+  position: 'bottom-right',
+})
+
+// React
+import { AIUIProvider } from '@aiui/widget/react'
+&lt;AIUIProvider apiKey="your-key" position="bottom-right" /&gt;</code></pre>
+          </div>
+
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">Option 4: iframe (maximum isolation)</h3>
+            <pre class="bg-gray-900 text-gray-100 rounded-lg p-4 overflow-x-auto text-xs"><code>&lt;iframe
+  src="https://app.aiui.dev/embed?key=your-key&amp;theme=dark"
+  style="position:fixed;bottom:80px;right:24px;width:420px;height:640px;
+         border:none;border-radius:16px;z-index:9999;"
+  allow="microphone"
+&gt;&lt;/iframe&gt;</code></pre>
+          </div>
+        </div>
+      </div>
+
+      <div class="bg-gray-50 rounded-2xl border border-gray-200 p-8">
+        <h2 class="text-xl font-bold mb-4">Technical Architecture</h2>
+        <div class="grid md:grid-cols-2 gap-8 text-sm text-gray-700">
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">Script Tag / npm</h3>
+            <ul class="space-y-1 list-disc list-inside">
+              <li>Injects a Vue micro-app into a shadow DOM container</li>
+              <li>Styles are encapsulated — no CSS conflicts with host</li>
+              <li>Communicates via CustomEvents or a global AIUI API object</li>
+              <li>Host app can pass context (current page, user info)</li>
+              <li>Smallest footprint: ~80KB gzipped</li>
+            </ul>
+          </div>
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">Web Component</h3>
+            <ul class="space-y-1 list-disc list-inside">
+              <li>Framework-agnostic Custom Element (works in any HTML)</li>
+              <li>Shadow DOM encapsulation by default</li>
+              <li>Attributes for configuration, events for callbacks</li>
+              <li>Can be lazy-loaded with dynamic import()</li>
+              <li>Works in React, Angular, Svelte, plain HTML</li>
+            </ul>
+          </div>
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">iframe</h3>
+            <ul class="space-y-1 list-disc list-inside">
+              <li>Maximum isolation — separate browsing context</li>
+              <li>Zero risk of CSS/JS conflicts</li>
+              <li>Communication via postMessage API</li>
+              <li>API key stays on embedded origin (more secure)</li>
+              <li>Slightly larger overhead, but simplest integration</li>
+            </ul>
+          </div>
+          <div>
+            <h3 class="font-semibold text-gray-900 mb-2">Host Communication</h3>
+            <ul class="space-y-1 list-disc list-inside">
+              <li>Host can send page context to AI for better answers</li>
+              <li>Widget can trigger actions in host app via callbacks</li>
+              <li>Conversation history syncs via encrypted IndexedDB</li>
+              <li>Deep-link support: <code class="bg-gray-200 px-1 rounded">?aiui=open&q=help</code></li>
+            </ul>
+          </div>
+        </div>
+      </div>
+    </div>
+
+    <AIUIWidget />
+  </div>
+</template>
+
+<script setup lang="ts">
+import { RouterLink } from 'vue-router'
+import AIUIWidget from '@/components/widget/AIUIWidget.vue'
+</script>
diff --git a/packages/app/src/stores/chat.ts b/packages/app/src/stores/chat.ts
new file mode 100644
index 00000000..86736d5c
--- /dev/null
+++ b/packages/app/src/stores/chat.ts
@@ -0,0 +1,95 @@
+import { defineStore } from 'pinia'
+import { ref, computed } from 'vue'
+import type { Message, Conversation } from '@aiui/core/types/message'
+
+export const useChatStore = defineStore('chat', () => {
+  const conversations = ref<Map<string, Conversation>>(new Map())
+  const activeConversationId = ref<string | null>(null)
+  const isStreaming = ref(false)
+  const panelSide = ref<'left' | 'right'>('right')
+
+  const activeConversation = computed(() => {
+    if (!activeConversationId.value) return null
+    return conversations.value.get(activeConversationId.value) ?? null
+  })
+
+  const messages = computed(() => activeConversation.value?.messages ?? [])
+
+  const conversationList = computed(() =>
+    Array.from(conversations.value.values()).sort((a, b) => b.updatedAt - a.updatedAt)
+  )
+
+  function createConversation(title = 'New Chat'): string {
+    const id = crypto.randomUUID()
+    const conversation: Conversation = {
+      id,
+      title,
+      messages: [],
+      createdAt: Date.now(),
+      updatedAt: Date.now(),
+    }
+    conversations.value.set(id, conversation)
+    activeConversationId.value = id
+    return id
+  }
+
+  function addMessage(conversationId: string, message: Omit<Message, 'id' | 'timestamp'>) {
+    const conv = conversations.value.get(conversationId)
+    if (!conv) return
+
+    const msg: Message = {
+      ...message,
+      id: crypto.randomUUID(),
+      timestamp: Date.now(),
+    }
+    conv.messages.push(msg)
+    conv.updatedAt = Date.now()
+
+    if (conv.messages.length === 1 && message.role === 'user') {
+      conv.title = message.content.slice(0, 60) + (message.content.length > 60 ? '...' : '')
+    }
+
+    return msg
+  }
+
+  function appendToLastMessage(conversationId: string, text: string) {
+    const conv = conversations.value.get(conversationId)
+    if (!conv || conv.messages.length === 0) return
+    const last = conv.messages[conv.messages.length - 1]
+    last.content += text
+  }
+
+  function switchSide() {
+    panelSide.value = panelSide.value === 'right' ? 'left' : 'right'
+  }
+
+  function setActiveConversation(id: string) {
+    if (conversations.value.has(id)) {
+      activeConversationId.value = id
+    }
+  }
+
+  function deleteConversation(id: string) {
+    conversations.value.delete(id)
+    if (activeConversationId.value === id) {
+      const remaining = conversationList.value
+      activeConversationId.value = remaining.length > 0 ? remaining[0].id : null
+    }
+  }
+
+  return {
+    conversations,
+    activeConversationId,
+    activeConversation,
+    messages,
+    conversationList,
+    isStreaming,
+    panelSide,
+    createConversation,
+    addMessage,
+    appendToLastMessage,
+    switchSide,
+    setActiveConversation,
+    deleteConversation,
+  }
+})
diff --git a/packages/app/src/styles/main.css b/packages/app/src/styles/main.css
index 82680ed1..312422a7 100644
--- a/packages/app/src/styles/main.css
+++ b/packages/app/src/styles/main.css
@@ -13,6 +13,14 @@
   --color-warning: #F59E0B;
   --color-info: #3B82F6;
 
+  --color-glass-bg: rgba(255, 255, 255, 0.08);
+  --color-glass-border: rgba(255, 255, 255, 0.12);
+  --color-glass-bg-hover: rgba(255, 255, 255, 0.14);
+  --color-glass-border-hover: rgba(255, 255, 255, 0.22);
+
+  --color-glass-bg-light: rgba(255, 255, 255, 0.65);
+  --color-glass-border-light: rgba(255, 255, 255, 0.45);
+
   --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
   --font-mono: 'Menlo', 'Monaco', 'Courier New', monospace;
 }
@@ -25,6 +33,111 @@ body {
   overscroll-behavior: none;
 }
 
+.glass {
+  background: var(--color-glass-bg);
+  backdrop-filter: blur(16px);
+  -webkit-backdrop-filter: blur(16px);
+  border: 1px solid var(--color-glass-border);
+}
+
+.glass-subtle {
+  background: rgba(255, 255, 255, 0.05);
+  backdrop-filter: blur(8px);
+  -webkit-backdrop-filter: blur(8px);
+  border: 1px solid rgba(255, 255, 255, 0.08);
+}
+
+.glass-strong {
+  background: rgba(255, 255, 255, 0.15);
+  backdrop-filter: blur(20px);
+  -webkit-backdrop-filter: blur(20px);
+  border: 1px solid rgba(255, 255, 255, 0.18);
+}
+
+.glass-light {
+  background: var(--color-glass-bg-light);
+  backdrop-filter: blur(16px);
+  -webkit-backdrop-filter: blur(16px);
+  border: 1px solid var(--color-glass-border-light);
+}
+
+.glass-dark {
+  background: rgba(0, 0, 0, 0.45);
+  backdrop-filter: blur(16px);
+  -webkit-backdrop-filter: blur(16px);
+  border: 1px solid rgba(255, 255, 255, 0.08);
+}
+
+.glass:hover {
+  background: var(--color-glass-bg-hover);
+  border-color: var(--color-glass-border-hover);
+}
+
+.glow-accent {
+  box-shadow: 0 0 20px rgba(247, 147, 26, 0.15),
+              0 0 40px rgba(247, 147, 26, 0.05);
+}
+
+.glow-soft {
+  box-shadow: 0 0 20px rgba(255, 255, 255, 0.06);
+}
+
+.inner-glow {
+  box-shadow: inset 0 1px 1px rgba(255, 255, 255, 0.06);
+}
+
+.gradient-text {
+  background: linear-gradient(to right, #ffffff, #9ca3af);
+  -webkit-background-clip: text;
+  background-clip: text;
+  color: transparent;
+}
+
+@keyframes fadeSlideUp {
+  from { opacity: 0; transform: translateY(12px); }
+  to { opacity: 1; transform: translateY(0); }
+}
+
+@keyframes scaleIn {
+  from { opacity: 0; transform: scale(0.92); }
+  to { opacity: 1; transform: scale(1); }
+}
+
+@keyframes pulseGlow {
+  0%, 100% { opacity: 0.4; }
+  50% { opacity: 1; }
+}
+
+.animate-fade-up {
+  animation: fadeSlideUp 0.3s cubic-bezier(0.16, 1, 0.3, 1) both;
+}
+
+.animate-scale-in {
+  animation: scaleIn 0.25s cubic-bezier(0.16, 1, 0.3, 1) both;
+}
+
+.animate-pulse-glow {
+  animation: pulseGlow 2s ease-in-out infinite;
+}
+
+.scrollbar-thin {
+  scrollbar-width: thin;
+  scrollbar-color: rgba(255, 255, 255, 0.15) transparent;
+}
+
+.scrollbar-thin::-webkit-scrollbar {
+  width: 4px;
+}
+
+.scrollbar-thin::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+.scrollbar-thin::-webkit-scrollbar-thumb {
+  background: rgba(255, 255, 255, 0.15);
+  border-radius: 2px;
+}
+
 @media (prefers-reduced-motion: reduce) {
   * {
     animation-duration: 0.01ms !important;