diff --git a/src/renderer/App.tsx b/src/renderer/App.tsx
index 35e1caa..b6464ea 100644
--- a/src/renderer/App.tsx
+++ b/src/renderer/App.tsx
@@ -7,12 +7,13 @@ import { useEditorStore } from './store/editorStore'
 import './styles/app.css'
 
 export default function App(): JSX.Element {
-  const { setFileTree, activeFilePath, isDirty, markSaved, activeFileContent } =
+  const { setFileTree, activeFilePath, isDirty, markSaved, activeFileContent, theme, toggleTheme } =
     useEditorStore()
 
-  // Load file tree on mount
+  // Load file tree on mount and apply persisted theme
   useEffect(() => {
     window.api.listFiles().then(setFileTree)
+    document.documentElement.classList.toggle('light', theme === 'light')
   }, [])
 
   // Handle Cmd+S / Ctrl+S
@@ -34,6 +35,13 @@ export default function App(): JSX.Element {
     <div className="app-layout">
       <div className="app-titlebar">
         <span className="app-titlebar-title">Hohoff Editor</span>
+        <button
+          className="app-titlebar-theme-btn"
+          onClick={toggleTheme}
+          title={theme === 'dark' ? 'Switch to light mode' : 'Switch to dark mode'}
+        >
+          {theme === 'dark' ? '☀' : '☾'}
+        </button>
       </div>
       <aside className="sidebar">
         <FileTree />
diff --git a/src/renderer/components/Editor/MarkdownEditor.tsx b/src/renderer/components/Editor/MarkdownEditor.tsx
index c1a0c47..e687323 100644
--- a/src/renderer/components/Editor/MarkdownEditor.tsx
+++ b/src/renderer/components/Editor/MarkdownEditor.tsx
@@ -46,7 +46,7 @@ const annotationField = StateField.define<DecorationSet>({
 
 const themeCompartment = new Compartment()
 
-function buildTheme(fontSize: number): ReturnType<typeof EditorView.theme> {
+function buildTheme(fontSize: number, dark: boolean): ReturnType<typeof EditorView.theme> {
   return EditorView.theme(
   {
     '&': {
@@ -67,8 +67,8 @@ function buildTheme(fontSize: number): ReturnType<typeof EditorView.theme> {
       caretColor: 'var(--accent)'
     },
     '.cm-cursor': { borderLeftColor: 'var(--accent)' },
-    '.cm-selectionBackground': { backgroundColor: 'rgba(167,139,95,0.2)' },
-    '&.cm-focused .cm-selectionBackground': { backgroundColor: 'rgba(167,139,95,0.3)' },
+    '.cm-selectionBackground': { backgroundColor: 'var(--active-bg)' },
+    '&.cm-focused .cm-selectionBackground': { backgroundColor: 'var(--active-bg)' },
     '.cm-line': { padding: '0', marginBottom: '6px' },
     '.cm-gutters': { display: 'none' },
     '.cm-activeLine': { backgroundColor: 'transparent' },
@@ -98,14 +98,14 @@ function buildTheme(fontSize: number): ReturnType<typeof EditorView.theme> {
       borderRadius: '2px'
     }
   },
-  { dark: true }
+  { dark }
   )
 }
 
 export function MarkdownEditor(): JSX.Element {
   const containerRef = useRef<HTMLDivElement>(null)
   const viewRef = useRef<EditorView | null>(null)
-  const { activeFilePath, activeFileContent, setContent, annotations, fontSize } = useEditorStore()
+  const { activeFilePath, activeFileContent, setContent, annotations, fontSize, theme } = useEditorStore()
 
   // Initialize CodeMirror once
   useEffect(() => {
@@ -120,7 +120,7 @@ export function MarkdownEditor(): JSX.Element {
           markdown(),
           syntaxHighlighting(defaultHighlightStyle),
           annotationField,
-          themeCompartment.of(buildTheme(fontSize)),
+          themeCompartment.of(buildTheme(fontSize, theme === 'dark')),
           EditorView.lineWrapping,
           EditorView.updateListener.of((update) => {
             if (update.docChanged) {
@@ -161,12 +161,12 @@ export function MarkdownEditor(): JSX.Element {
     view.dispatch({ effects: setAnnotationsEffect.of(annotations) })
   }, [annotations])
 
-  // Reconfigure theme when font size changes
+  // Reconfigure theme when font size or colour theme changes
   useEffect(() => {
     const view = viewRef.current
     if (!view) return
-    view.dispatch({ effects: themeCompartment.reconfigure(buildTheme(fontSize)) })
-  }, [fontSize])
+    view.dispatch({ effects: themeCompartment.reconfigure(buildTheme(fontSize, theme === 'dark')) })
+  }, [fontSize, theme])
 
   return (
     <div className="editor-container">
diff --git a/src/renderer/store/editorStore.ts b/src/renderer/store/editorStore.ts
index 4c1735a..de45f0d 100644
--- a/src/renderer/store/editorStore.ts
+++ b/src/renderer/store/editorStore.ts
@@ -42,6 +42,10 @@ interface EditorState {
   // Editor font size
   fontSize: number
   setFontSize: (size: number) => void
+
+  // Theme
+  theme: 'dark' | 'light'
+  toggleTheme: () => void
 }
 
 export const useEditorStore = create<EditorState>((set, get) => ({
@@ -133,5 +137,15 @@ export const useEditorStore = create<EditorState>((set, get) => ({
     const clamped = Math.max(11, Math.min(24, size))
     localStorage.setItem('editorFontSize', String(clamped))
     set({ fontSize: clamped })
+  },
+
+  theme: (localStorage.getItem('editorTheme') as 'dark' | 'light') || 'dark',
+  toggleTheme: () => {
+    set((s) => {
+      const next = s.theme === 'dark' ? 'light' : 'dark'
+      localStorage.setItem('editorTheme', next)
+      document.documentElement.classList.toggle('light', next === 'light')
+      return { theme: next }
+    })
   }
 }))
diff --git a/src/renderer/styles/app.css b/src/renderer/styles/app.css
index b8b9327..676c12f 100644
--- a/src/renderer/styles/app.css
+++ b/src/renderer/styles/app.css
@@ -28,6 +28,25 @@
   text-transform: uppercase;
 }
 
+.app-titlebar-theme-btn {
+  position: absolute;
+  right: 12px;
+  background: none;
+  border: none;
+  color: var(--text-muted);
+  font-size: 13px;
+  cursor: pointer;
+  padding: 2px 4px;
+  border-radius: 4px;
+  line-height: 1;
+  -webkit-app-region: no-drag;
+  transition: color 0.15s;
+}
+
+.app-titlebar-theme-btn:hover {
+  color: var(--text-primary);
+}
+
 /* ─── Sidebar ──────────────────────────────────────────────────── */
 .sidebar {
   background: var(--sidebar-bg);
diff --git a/src/renderer/styles/global.css b/src/renderer/styles/global.css
index 4f3987e..55db3d3 100644
--- a/src/renderer/styles/global.css
+++ b/src/renderer/styles/global.css
@@ -38,6 +38,30 @@
   --font-sans:      -apple-system, 'Segoe UI', Helvetica, Arial, sans-serif;
 }
 
+/* ─── Light mode token overrides (sepia) ──────────────────────── */
+html.light {
+  --bg-base:        #f2ead8;
+  --sidebar-bg:     #e8dfc8;
+  --toolbar-bg:     #ddd4bc;
+  --editor-bg:      #f2ead8;
+  --message-bg:     #e8dfc8;
+  --user-message-bg:#ddd4bc;
+  --input-bg:       #e8dfc8;
+
+  --border:         #c4b89a;
+  --hover-bg:       rgba(120,88,40,0.08);
+  --active-bg:      rgba(120,88,40,0.15);
+
+  --text-primary:   #241c0e;
+  --text-secondary: #52401e;
+  --text-muted:     #7a6640;
+
+  --heading-color:  #3c2c0e;
+
+  --accent:         #7a5c28;
+  --accent-hover:   #9a7030;
+}
+
 /* ─── Base ─────────────────────────────────────────────────────── */
 html, body, #root {
   height: 100%;