diff --git a/src/App.tsx b/src/App.tsx
index 6e1ab8d..4c495f8 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -328,6 +328,9 @@ function App() {
   const [showShortcutsModal, setShowShortcutsModal] = useState(false);
   const [showAboutModal, setShowAboutModal] = useState(false);
   const [zoom, setZoom] = useState(100);
+  const [theme, setTheme] = useState<'dark' | 'light'>(() => {
+    return (localStorage.getItem('vesper-theme') as 'dark' | 'light') || 'dark';
+  });
   const [uiZoom, setUiZoom] = useState(() => {
     const saved = localStorage.getItem('vesper-ui-zoom');
     return saved ? parseInt(saved, 10) : 100;
@@ -863,6 +866,11 @@ function App() {
     localStorage.setItem('vesper-ui-zoom', String(Math.round(uiZoom)));
   }, [uiZoom]);
 
+  // Persist theme to localStorage
+  useEffect(() => {
+    localStorage.setItem('vesper-theme', theme);
+  }, [theme]);
+
   // Menu bar keyboard navigation (WAI-ARIA menu pattern)
   const handleMenuBarKeyDown = (e: React.KeyboardEvent) => {
     if (e.key === 'ArrowRight') {
@@ -1080,7 +1088,7 @@ function App() {
   };
 
   return (
-    <div className={`app-container ${focusMode ? 'focus-mode' : ''}`} style={{ zoom: `${uiZoom}%` }}>
+    <div className={`app-container ${focusMode ? 'focus-mode' : ''} ${theme === 'light' ? 'theme-light' : ''}`} style={{ zoom: `${uiZoom}%` }}>
       <a href="#main-content" className="skip-link">Skip to content</a>
       <AnimatePresence>
         {isDraggingOver && (
@@ -1133,6 +1141,7 @@ function App() {
                   <button className="menu-dropdown-item" role="menuitem" onClick={() => { setShowSearch(s => !s); setMenuOpen(null); }}>Toggle Search <span className="menu-shortcut">Ctrl+F</span></button>
                   <button className="menu-dropdown-item" role="menuitem" onClick={() => { setShowSidebar(s => !s); setMenuOpen(null); }}>Toggle Sidebar <span className="menu-shortcut">Ctrl+Shift+S</span></button>
                   <button className="menu-dropdown-item" role="menuitem" onClick={() => { setFocusMode(f => !f); setMenuOpen(null); }}>Focus Mode <span className="menu-shortcut">F11</span></button>
+                  <button className="menu-dropdown-item" role="menuitem" onClick={() => { setTheme(t => t === 'dark' ? 'light' : 'dark'); setMenuOpen(null); }}>Theme: {theme === 'dark' ? 'Dark' : 'Light'} <span className="menu-shortcut">{theme === 'dark' ? 'Switch to Light' : 'Switch to Dark'}</span></button>
                   <div className="menu-separator"></div>
                   <div className="menu-dropdown-zoom" onClick={e => e.stopPropagation()}>
                     <span>UI Scale</span>
diff --git a/src/styles.css b/src/styles.css
index 2d157ca..0f04fd8 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -1674,6 +1674,128 @@ input:focus-visible,
   z-index: 1;
 }
 
+/* ============================================
+   Light theme overrides — WCAG 1.4.8
+   ============================================ */
+.theme-light {
+  --color-bg-base: #F5F6F8;
+  --color-bg-surface: #EBEDF0;
+  --color-bg-elevated: #FFFFFF;
+  --color-bg-overlay: #FFFFFF;
+  --color-bg-hover: #E2E4E8;
+  --color-bg-active: #D5D8DD;
+
+  --color-text-primary: #1A1D24;
+  --color-text-secondary: #4A5060;
+  --color-text-tertiary: #6B7280;
+  --color-text-disabled: #9CA3AF;
+
+  --color-accent: #3B66E0;
+  --color-accent-hover: #2B52CC;
+  --color-accent-muted: rgba(59, 102, 224, 0.10);
+  --color-accent-subtle: rgba(59, 102, 224, 0.05);
+  --color-accent-small: #2B52CC;
+
+  --color-border-subtle: rgba(0, 0, 0, 0.06);
+  --color-border: rgba(0, 0, 0, 0.10);
+  --color-border-strong: rgba(0, 0, 0, 0.16);
+
+  /* Markdown typography — light variants */
+  --color-md-h1: #111318;
+  --color-md-h2: #1A1D24;
+  --color-md-h3: #252A31;
+  --color-md-h4: #333942;
+  --color-md-h5: #404754;
+  --color-md-h6: #4A5060;
+  --color-md-heading: #1A1D24;
+  --color-md-paragraph: #333942;
+  --color-md-link: #2B5BC2;
+  --color-md-link-underline: rgba(43, 91, 194, 0.3);
+  --color-md-link-hover: #1E4AAE;
+  --color-md-link-hover-underline: rgba(30, 74, 174, 0.5);
+  --color-md-marker: #3B66E0;
+  --color-md-blockquote-border: #3B66E0;
+  --color-md-blockquote-bg: rgba(59, 102, 224, 0.04);
+  --color-md-blockquote-text: #4A5060;
+  --color-md-code-inline: #B35C2A;
+  --color-md-code-inline-bg: rgba(0, 0, 0, 0.04);
+  --color-md-code-block-bg: #F0F1F3;
+  --color-md-code-block-border: rgba(0, 0, 0, 0.08);
+  --color-md-code-text: #1A1D24;
+  --color-md-table-header-bg: rgba(59, 102, 224, 0.06);
+  --color-md-table-border: rgba(0, 0, 0, 0.08);
+  --color-md-table-cell: #333942;
+  --color-md-table-stripe: rgba(0, 0, 0, 0.02);
+  --color-md-table-hover: rgba(59, 102, 224, 0.04);
+  --color-md-hr: rgba(0, 0, 0, 0.1);
+  --color-md-mark-bg: rgba(251, 191, 36, 0.25);
+  --color-md-mark-text: #92650B;
+  --color-md-comment: #6B7280;
+  --color-md-highlight-bg: rgba(251, 191, 36, 0.3);
+  --color-md-highlight-active-bg: rgba(251, 191, 36, 0.5);
+  --color-md-highlight-active-outline: rgba(200, 150, 20, 0.7);
+  --color-md-welcome-btn: #3B66E0;
+}
+
+/* Light theme — noise overlay should be darker */
+.theme-light.app-container::before {
+  opacity: 0.025;
+  mix-blend-mode: multiply;
+}
+
+/* Light theme — title bar close button */
+.theme-light .title-bar-button.close:hover {
+  background-color: #DC2626;
+  color: white;
+}
+
+/* Light theme — scrollbar colors */
+.theme-light .os-theme-dark {
+  --os-handle-bg: rgba(0, 0, 0, 0.15);
+  --os-handle-bg-hover: var(--color-accent);
+  --os-handle-bg-active: var(--color-accent-hover);
+}
+
+/* Light theme — sidebar resize handle */
+.theme-light .sidebar-resize-handle {
+  background: rgba(0, 0, 0, 0.06);
+}
+
+.theme-light .sidebar-resize-handle:hover,
+.theme-light .sidebar-resize-handle:focus-visible {
+  background-color: var(--color-accent);
+}
+
+/* Light theme syntax highlighting */
+.theme-light .hljs { color: #1A1D24; }
+.theme-light .hljs-keyword,
+.theme-light .hljs-selector-tag,
+.theme-light .hljs-literal,
+.theme-light .hljs-section,
+.theme-light .hljs-link { color: #7C3AED; font-weight: 500; }
+
+.theme-light .hljs-string,
+.theme-light .hljs-title,
+.theme-light .hljs-name,
+.theme-light .hljs-type,
+.theme-light .hljs-attribute,
+.theme-light .hljs-symbol,
+.theme-light .hljs-bullet,
+.theme-light .hljs-addition,
+.theme-light .hljs-variable,
+.theme-light .hljs-template-tag,
+.theme-light .hljs-template-variable { color: #16652B; }
+
+.theme-light .hljs-comment,
+.theme-light .hljs-quote,
+.theme-light .hljs-deletion,
+.theme-light .hljs-meta { color: var(--color-md-comment); font-style: italic; }
+
+.theme-light .hljs-number { color: #C2410C; font-weight: 500; }
+.theme-light .hljs-built_in { color: #2563EB; }
+.theme-light .hljs-class .hljs-title { color: #B45309; }
+.theme-light .hljs-attr { color: #B45309; }
+
 /* Reduced motion */
 @media (prefers-reduced-motion: reduce) {
   *,