diff --git a/ui/src/App.jsx b/ui/src/App.jsx
index c3e532a..e4d4e3f 100644
--- a/ui/src/App.jsx
+++ b/ui/src/App.jsx
@@ -13,7 +13,7 @@ export default function App() {
   useEffect(() => { localStorage.setItem('pf_sidebar', sidebarExpanded ? 'expanded' : 'collapsed') }, [sidebarExpanded])
 
   return (
-    <div className="flex h-screen w-full bg-gray-100 text-sm text-gray-800 overflow-hidden">
+    <div className="flex h-screen w-full text-sm overflow-hidden">
       <Sidebar view={view} setView={setView} expanded={sidebarExpanded} setExpanded={setSidebarExpanded} />
       <div className="flex flex-col flex-1 overflow-hidden min-w-0">
         <StatusBar />
@@ -25,4 +25,4 @@ export default function App() {
       </div>
     </div>
   )
-}
+}
\ No newline at end of file
diff --git a/ui/src/components/Sidebar.jsx b/ui/src/components/Sidebar.jsx
index 8f55fa4..788b3c8 100644
--- a/ui/src/components/Sidebar.jsx
+++ b/ui/src/components/Sidebar.jsx
@@ -38,7 +38,6 @@ export default function Sidebar({ view, setView, expanded, setExpanded }) {
       className="bg-white border-r border-gray-200 flex flex-col shrink-0 overflow-hidden transition-all duration-150"
       style={{ width: expanded ? 200 : 48 }}
     >
-      {/* Logo / toggle */}
       <div className="h-12 flex items-center px-3 border-b border-gray-100 gap-2 shrink-0">
         <button
           onClick={() => setExpanded(e => !e)}
@@ -59,7 +58,6 @@ export default function Sidebar({ view, setView, expanded, setExpanded }) {
         </span>
       </div>
 
-      {/* Nav */}
       <nav className="flex flex-col gap-0.5 p-2 flex-1">
         {NAV.map(item => {
           const active = view === item.id
@@ -87,4 +85,4 @@ export default function Sidebar({ view, setView, expanded, setExpanded }) {
       </nav>
     </div>
   )
-}
+}
\ No newline at end of file
diff --git a/ui/src/components/StatusBar.jsx b/ui/src/components/StatusBar.jsx
index 6050e16..d1a62dc 100644
--- a/ui/src/components/StatusBar.jsx
+++ b/ui/src/components/StatusBar.jsx
@@ -1,6 +1,10 @@
+import useTheme from '../theme.jsx'
+
 export default function StatusBar() {
+  const { dark, setDark } = useTheme()
+
   return (
-    <div className="bg-white border-b border-gray-100 px-4 h-8 flex items-center gap-4 shrink-0 text-xs">
+    <div className="bg-white border-b border-gray-200 px-4 h-8 flex items-center gap-4 shrink-0 text-xs">
       <span className="text-gray-400">Source</span>
       <span className="font-medium text-gray-700">sales_orders</span>
       <span className="text-gray-200">|</span>
@@ -12,6 +16,23 @@ export default function StatusBar() {
       <span className="text-gray-200">|</span>
       <span className="text-gray-400">Status</span>
       <span className="text-green-600 font-medium">open</span>
+      <div className="ml-auto">
+        <button
+          onClick={() => setDark(d => !d)}
+          className="w-6 h-6 flex items-center justify-center rounded hover:bg-gray-100"
+          title={dark ? 'Switch to light mode' : 'Switch to dark mode'}
+        >
+          {dark ? (
+            <svg width="14" height="14" viewBox="0 0 16 16" fill="currentColor">
+              <path d="M8 12a4 4 0 1 0 0-8 4 4 0 0 0 0 8zM8 0a.5.5 0 0 1 .5.5v2a.5.5 0 0 1-1 0v-2A.5.5 0 0 1 8 0zm0 13a.5.5 0 0 1 .5.5v2a.5.5 0 0 1-1 0v-2A.5.5 0 0 1 8 13zm8-5a.5.5 0 0 1-.5.5h-2a.5.5 0 0 1 0-1h2a.5.5 0 0 1 .5.5zM3 8a.5.5 0 0 1-.5.5h-2a.5.5 0 0 1 0-1h2A.5.5 0 0 1 3 8z"/>
+            </svg>
+          ) : (
+            <svg width="14" height="14" viewBox="0 0 16 16" fill="currentColor">
+              <path d="M6 .278a.768.768 0 0 1 1.065.02A.75.75 0 0 1 5.792 15.5a.75.75 0 0 1-1.498-.075.768.768 0 0 1-.02-1.05A8 8 0 1 0 6.278 14.72a.768.768 0 0 1-1.055-.02A.75.75 0 0 1 2.5 13.75a.75.75 0 0 1 1.498.075A8 8 0 1 0 6 .278z"/>
+            </svg>
+          )}
+        </button>
+      </div>
     </div>
   )
-}
+}
\ No newline at end of file
diff --git a/ui/src/index.css b/ui/src/index.css
index ab0d6a7..86280ca 100644
--- a/ui/src/index.css
+++ b/ui/src/index.css
@@ -1,4 +1,80 @@
 @import "tailwindcss";
 
-body { margin: 0; }
+:root, .light {
+  --bg-primary: #f3f4f6;
+  --bg-secondary: #ffffff;
+  --bg-tertiary: #f9fafb;
+  --text-primary: #1f2937;
+  --text-secondary: #374151;
+  --text-muted: #9ca3af;
+  --border-color: #e5e7eb;
+  --border-light: #f3f4f6;
+  --accent-bg: #eff6ff;
+  --accent-text: #1d4ed8;
+}
+
+.dark {
+  --bg-primary: #111827;
+  --bg-secondary: #1f2937;
+  --bg-tertiary: #374151;
+  --text-primary: #f9fafb;
+  --text-secondary: #e5e7eb;
+  --text-muted: #6b7280;
+  --border-color: #374151;
+  --border-light: #1f2937;
+  --accent-bg: #1e3a5f;
+  --accent-text: #60a5fa;
+}
+
+body { margin: 0; background-color: var(--bg-primary); color: var(--text-primary); }
 #root { height: 100vh; display: flex; }
+
+.dark .bg-white { background-color: var(--bg-secondary); }
+.dark .bg-gray-50 { background-color: var(--bg-tertiary); }
+.dark .bg-gray-100 { background-color: var(--bg-tertiary); }
+.dark .bg-gray-200 { background-color: var(--bg-tertiary); }
+.dark .bg-gray-300 { background-color: var(--bg-tertiary); }
+.dark .text-gray-300 { color: var(--text-muted); }
+.dark .text-gray-400 { color: var(--text-muted); }
+.dark .text-gray-500 { color: var(--text-muted); }
+.dark .text-gray-600 { color: var(--text-secondary); }
+.dark .text-gray-700 { color: var(--text-secondary); }
+.dark .text-gray-800 { color: var(--text-primary); }
+.dark .text-gray-900 { color: var(--text-primary); }
+.dark .bg-blue-50 { background-color: var(--accent-bg); }
+.dark .bg-blue-100 { background-color: var(--accent-bg); }
+.dark .text-blue-600 { color: var(--accent-text); }
+.dark .text-blue-700 { color: var(--accent-text); }
+.dark .border-blue-300 { border-color: var(--accent-text); }
+.dark .hover\:bg-blue-50:hover { background-color: var(--accent-bg); }
+.dark .bg-green-50 { background-color: #064e3b; }
+.dark .text-green-600 { color: #34d399; }
+.dark .text-green-700 { color: #34d399; }
+.dark .text-green-400 { color: #34d399; }
+.dark .bg-yellow-50 { background-color: #451a03; }
+.dark .text-yellow-700 { color: #fbbf24; }
+.dark .bg-purple-50 { background-color: #1e1b4b; }
+.dark .text-purple-700 { color: #a78bfa; }
+.dark .bg-red-50 { background-color: #450a0a; }
+.dark .text-red-700 { color: #f87171; }
+.dark .border-gray-100 { border-color: var(--border-light); }
+.dark .border-gray-200 { border-color: var(--border-color); }
+.dark .border-gray-300 { border-color: var(--border-color); }
+.dark .border-b { border-color: var(--border-color); }
+.dark .border-t { border-color: var(--border-color); }
+.dark .border-r { border-color: var(--border-color); }
+.dark .border-l { border-color: var(--border-color); }
+.dark .hover\:bg-gray-50:hover { background-color: var(--bg-tertiary); }
+.dark .hover\:bg-gray-100:hover { background-color: var(--bg-tertiary); }
+.dark .hover\:bg-gray-200:hover { background-color: var(--bg-tertiary); }
+.dark .hover\:text-gray-500:hover { color: var(--text-secondary); }
+.dark .hover\:text-gray-600:hover { color: var(--text-secondary); }
+.dark .hover\:text-gray-800:hover { color: var(--text-primary); }
+.dark .hover\:border-gray-300:hover { border-color: var(--border-color); }
+.dark .hover\:border-gray-400:hover { border-color: var(--border-color); }
+.dark .focus\:border-gray-300:focus { border-color: var(--border-color); }
+.dark ::selection { background-color: var(--accent-bg); color: var(--accent-text); }
+.dark input { background-color: var(--bg-secondary); color: var(--text-primary); }
+.dark select { background-color: var(--bg-secondary); color: var(--text-primary); }
+.dark textarea { background-color: var(--bg-secondary); color: var(--text-primary); }
+.dark .bg-transparent { background-color: transparent; }
diff --git a/ui/src/main.jsx b/ui/src/main.jsx
index b9a1a6d..28ad15f 100644
--- a/ui/src/main.jsx
+++ b/ui/src/main.jsx
@@ -1,10 +1,13 @@
 import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
+import { ThemeProvider } from './theme.jsx'
 import './index.css'
 import App from './App.jsx'
 
 createRoot(document.getElementById('root')).render(
   <StrictMode>
-    <App />
+    <ThemeProvider>
+      <App />
+    </ThemeProvider>
   </StrictMode>,
 )
diff --git a/ui/src/theme.jsx b/ui/src/theme.jsx
new file mode 100644
index 0000000..afd26ce
--- /dev/null
+++ b/ui/src/theme.jsx
@@ -0,0 +1,25 @@
+import { createContext, useContext, useState, useEffect } from 'react'
+
+const ThemeContext = createContext()
+
+export function ThemeProvider({ children }) {
+  const [dark, setDark] = useState(() => {
+    const saved = localStorage.getItem('pf_dark')
+    if (saved !== null) return saved === 'true'
+    return window.matchMedia('(prefers-color-scheme: dark)').matches
+  })
+
+  useEffect(() => {
+    localStorage.setItem('pf_dark', dark)
+    document.documentElement.classList.toggle('dark', dark)
+  }, [dark])
+
+  return (
+    <ThemeContext.Provider value={{ dark, setDark }}>
+      {children}
+    </ThemeContext.Provider>
+  )
+}
+
+const useTheme = () => useContext(ThemeContext)
+export default useTheme
\ No newline at end of file